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Pediatric Orbit Tumors and Tumorlike Lesions: Nonosseous Lesions of the Extraocular Orbit¹

¹ From the Department of Radiologic Pathology (E.M.C.) and Ophthalmic Pathology Section, Department of Neuropathology (C.S.S.), Armed Forces Institute of Pathology, 6825 16th St NW, Washington, DC 20306-6000; Department of Radiology and Radiological Sciences, Edward F. Hebert School of Medicine, Uniformed University of the Health Sciences, Bethesda, Md (J.G.S., R.C.); National Capitol Radiology Consortium, National Naval Medical Center, Bethesda, Md (J.W.S.); and Department of Radiology, Walter Reed Army Medical Center, Washington, DC (J.W.S.). Received June 18, 2007; revision requested July 19 and received July 31; accepted August 3. All authors have no financial relationships to disclose. Address correspondence to E.M.C. (e-mail: chunge{at}afip.osd.mil).

	Abstract

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Rhabdomyosarcoma Vasculogenic Lesions Infantile Fibromatosis Summary References

 
The histologic spectrum of nonosseous tumors and tumorlike lesions of the extraocular orbit in children differs from that in adults, and the appearance of these lesions at imaging reflects their pathologic features. Rhabdomyosarcoma is the most common extraocular orbital tumor in children. This neoplasm usually manifests in young children, grows quite rapidly, and is fairly vascular. Vasculogenic lesions are common orbital lesions in newborns and young infants. The most prevalent of these are infantile hemangioma, a true neoplasm, and venous-lymphatic malformation, a developmental anomaly. Hemangioma is quite vascular, has a predictable course of proliferation followed by slow involution, and is distinguished on magnetic resonance images by the finding of flow voids within the mass and at its periphery. Venous-lymphatic malformation in the orbit is an anomaly of venous and lymphatic development that is characterized by unenhancing, cystic lymphatic and enhancing, solid venous components. Intralesional hemorrhage is common and frequently produces distinctive fluid-fluid levels within the cystic portions. Unlike hemangiomas, venous-lymphatic malformations grow with the patient and never involute spontaneously. Infantile fibromatosis is one of the fibromatoses and affects newborns and young infants. The tumor is nodular and composed of a zonal architecture, with frequent hemorrhage or necrosis in the central portion, characteristics that confer a target appearance at imaging. These lesions usually stop growing or spontaneously regress. All of these extraocular masses typically manifest with proptosis, and imaging differentiation is desirable because the treatments and prognoses vary greatly.

	LEARNING OBJECTIVES FOR TEST 6

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Rhabdomyosarcoma Vasculogenic Lesions Infantile Fibromatosis Summary References

 
After reading this article and taking the test, the reader will be able to:

• Describe the imaging features of extraocular orbital masses and their pathologic basis in children.
  
• Identify the features of extraocular orbital masses that may allow differentiation from other orbital tumors in children.
  
• Discuss the differential diagnosis of nonosseous, extraocular orbital masses and management of pediatric patients with these conditions.
  

	Introduction

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Rhabdomyosarcoma Vasculogenic Lesions Infantile Fibromatosis Summary References

 
Nonosseous, extraocular orbital tumors are uncommon in children and represent a different histologic spectrum than is seen in adults. Most of these lesions are mesenchymal in origin. The most common mesenchymal tumor of childhood is rhabdomyosarcoma, which may arise in or invade the orbit in young children. Vasculogenic lesions, both vascular tumors and developmental malformations, also occur in the orbit. Hemangiomas are true neoplasms that are found in infants and are distinguished by their high-flow feeding vessels. Venous-lymphatic malformations, or lymphangiomas, occur in the same age group as rhabdomyosarcoma, but they are distinguished by their cystic components and frequent fluid-fluid levels related to intralesional hemorrhage. Infantile or juvenile fibromatosis is a rare, benign fibrous proliferation that may manifest as a solitary mass in the orbit and that may be distinguished by central necrosis or hemorrhage. These lesions, as well as other orbital lesions (including those arising from the globe, optic nerve, and bony orbit), most commonly manifest with the clinical finding of proptosis. The treatment and prognosis of orbital lesions are widely varied, and imaging studies may help in their diagnosis and management. In this article, the clinical, pathologic, and imaging features of these lesions are described and correlated, and the differential diagnoses are reviewed.

	Rhabdomyosarcoma

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Rhabdomyosarcoma Vasculogenic Lesions Infantile Fibromatosis Summary References

 
Rhabdomyosarcoma is the most common mesenchymal tumor in children, accounting for about 5% of all childhood cancers (1,2), and the most prevalent extraocular orbital malignancy in children, although it is only one-tenth as common as retinoblastoma, which is itself a rare tumor (3–5). Over one-third (35%–40%) of rhabdomyosarcomas arise in the head and neck, and orbital primary tumors account for about 25%–35% of head and neck rhabdomyosarcomas and about 10% of all rhabdomyosarcomas (6–8). The orbit can also be involved secondarily by the spread of tumors originating in the nasopharynx, pterygopalatine fossa, infratemporal fossa, or paranasal sinuses (the so-called parameningeal sites) or as a site of metastasis (7). The most common histologic type to involve the orbit is the embryonal form.

Rhabdomyosarcoma was previously thought to arise from skeletal muscle (eg, extraocular muscles in the orbit), but now it is generally believed to originate from pluripotential mesenchymal cells that have the capacity to differentiate into skeletal muscle. This explanation clarifies why primary rhabdomyosarcomas occur in siteswhere there is no skeletal muscle, such as the nasopharynx, paranasal sinuses, and bile duct (4,8).

Epidemiology and Clinical Features
Primary orbital rhabdomyosarcoma most often occurs in the first decade of life, with a mean patient age of 6–8 years (3,4,6), but it has been reported in patients of all age groups, from infancy to age 68 years (3). The less common alveolar form generally affects older children or adolescents (4). There is a slight male predilection, with a male-to-female ratio of 5:3 (1,6,9).

Rhabdomyosarcoma is an aggressive, rapidly growing tumor and most often manifests with rapidly progressive proptosis or globe displacement. Other common signs and symptoms include conjunctival and palpebral swelling, which may suggest the clinical diagnosis of orbital cellulitis (1,9).

Rhabdomyosarcomas are always unilateral, although Sohaib et al (10) reported a case of one patient with multicentric disease in one eye. Most tumors are extraconal (37%–87% of cases) or both intra- and extraconal (13%–47%) (10). The most typical locations are the superonasal quadrant and the superior orbit for the more common embryonal type. Approximately 33%–53% of orbital embryonal rhabdomyosarcomas occur in these locations (1,10). The less prevalent alveolar form more often affects the inferior orbit (4,10).

Pathologic Features
Rhabdomyosarcomas are soft, fleshy, and light gray to pink or yellow on cut sections. Tumors with abundant cellular matrix may demonstrate a myxoid appearance. Tumor margins, particularly in smaller masses, may be circumscribed (Fig 1e). Larger masses have irregular borders because the pseudocapsule has been invaded. Some tumors may reveal areas of hemorrhage or cyst formation (4,6).

View larger version (145K): [in this window] [in a new window] [Download PPT slide]   Figure 1a.  Embryonal rhabdomyosarcoma with alveolar features in an 18-year-old boy with left proptosis. (a) Sagittal T1-weighted magnetic resonance (MR) image shows a well-circumscribed extraconal mass (arrowhead) superior to the ocular globe and isointense relative to muscle. (b) Another sagittal MR image shows that the mass is separate from the superior rectus muscle (arrow). (c) On the axial T2-weighted image, the mass is heterogeneous in signal intensity and predominantly hyperintense relative to gray matter and muscle. (d) Coronal T1-weighted image obtained after intravenous administration of gadolinium-based contrast material reveals intense enhancement of the tumor. (e) Photograph of the gross specimen shows it to be a well-circumscribed, fleshy tumor. Scale is in centimeters. (f) Photomicrograph (original magnification x200; hematoxylin-eosin [H-E] stain) shows pleomorphic (spindle-shaped and round) rhabdomyosarcomatous cells arranged in an alveolar pattern within a collagenized stroma. (g) Higher power photomicrograph (original magnification x400; H-E stain) of the same tumor specimen but from another area shows neoplastic cells with hyperchromatic, pleomorphic nuclei and scant cytoplasm distributed through a myxoid matrix. Fibrillary structures suggestive of cross striations may be seen in rare cells that have more ample cytoplasm and vesicular nuclei (straight arrow). Note numerous mitotic figures (arrowheads) and occasional pyknotic nuclei (tailed arrow).

View larger version (143K): [in this window] [in a new window] [Download PPT slide]   Figure 1b.  Embryonal rhabdomyosarcoma with alveolar features in an 18-year-old boy with left proptosis. (a) Sagittal T1-weighted magnetic resonance (MR) image shows a well-circumscribed extraconal mass (arrowhead) superior to the ocular globe and isointense relative to muscle. (b) Another sagittal MR image shows that the mass is separate from the superior rectus muscle (arrow). (c) On the axial T2-weighted image, the mass is heterogeneous in signal intensity and predominantly hyperintense relative to gray matter and muscle. (d) Coronal T1-weighted image obtained after intravenous administration of gadolinium-based contrast material reveals intense enhancement of the tumor. (e) Photograph of the gross specimen shows it to be a well-circumscribed, fleshy tumor. Scale is in centimeters. (f) Photomicrograph (original magnification x200; hematoxylin-eosin [H-E] stain) shows pleomorphic (spindle-shaped and round) rhabdomyosarcomatous cells arranged in an alveolar pattern within a collagenized stroma. (g) Higher power photomicrograph (original magnification x400; H-E stain) of the same tumor specimen but from another area shows neoplastic cells with hyperchromatic, pleomorphic nuclei and scant cytoplasm distributed through a myxoid matrix. Fibrillary structures suggestive of cross striations may be seen in rare cells that have more ample cytoplasm and vesicular nuclei (straight arrow). Note numerous mitotic figures (arrowheads) and occasional pyknotic nuclei (tailed arrow).

View larger version (134K): [in this window] [in a new window] [Download PPT slide]   Figure 1c.  Embryonal rhabdomyosarcoma with alveolar features in an 18-year-old boy with left proptosis. (a) Sagittal T1-weighted magnetic resonance (MR) image shows a well-circumscribed extraconal mass (arrowhead) superior to the ocular globe and isointense relative to muscle. (b) Another sagittal MR image shows that the mass is separate from the superior rectus muscle (arrow). (c) On the axial T2-weighted image, the mass is heterogeneous in signal intensity and predominantly hyperintense relative to gray matter and muscle. (d) Coronal T1-weighted image obtained after intravenous administration of gadolinium-based contrast material reveals intense enhancement of the tumor. (e) Photograph of the gross specimen shows it to be a well-circumscribed, fleshy tumor. Scale is in centimeters. (f) Photomicrograph (original magnification x200; hematoxylin-eosin [H-E] stain) shows pleomorphic (spindle-shaped and round) rhabdomyosarcomatous cells arranged in an alveolar pattern within a collagenized stroma. (g) Higher power photomicrograph (original magnification x400; H-E stain) of the same tumor specimen but from another area shows neoplastic cells with hyperchromatic, pleomorphic nuclei and scant cytoplasm distributed through a myxoid matrix. Fibrillary structures suggestive of cross striations may be seen in rare cells that have more ample cytoplasm and vesicular nuclei (straight arrow). Note numerous mitotic figures (arrowheads) and occasional pyknotic nuclei (tailed arrow).

View larger version (131K): [in this window] [in a new window] [Download PPT slide]   Figure 1d.  Embryonal rhabdomyosarcoma with alveolar features in an 18-year-old boy with left proptosis. (a) Sagittal T1-weighted magnetic resonance (MR) image shows a well-circumscribed extraconal mass (arrowhead) superior to the ocular globe and isointense relative to muscle. (b) Another sagittal MR image shows that the mass is separate from the superior rectus muscle (arrow). (c) On the axial T2-weighted image, the mass is heterogeneous in signal intensity and predominantly hyperintense relative to gray matter and muscle. (d) Coronal T1-weighted image obtained after intravenous administration of gadolinium-based contrast material reveals intense enhancement of the tumor. (e) Photograph of the gross specimen shows it to be a well-circumscribed, fleshy tumor. Scale is in centimeters. (f) Photomicrograph (original magnification x200; hematoxylin-eosin [H-E] stain) shows pleomorphic (spindle-shaped and round) rhabdomyosarcomatous cells arranged in an alveolar pattern within a collagenized stroma. (g) Higher power photomicrograph (original magnification x400; H-E stain) of the same tumor specimen but from another area shows neoplastic cells with hyperchromatic, pleomorphic nuclei and scant cytoplasm distributed through a myxoid matrix. Fibrillary structures suggestive of cross striations may be seen in rare cells that have more ample cytoplasm and vesicular nuclei (straight arrow). Note numerous mitotic figures (arrowheads) and occasional pyknotic nuclei (tailed arrow).

View larger version (125K): [in this window] [in a new window] [Download PPT slide]   Figure 1e.  Embryonal rhabdomyosarcoma with alveolar features in an 18-year-old boy with left proptosis. (a) Sagittal T1-weighted magnetic resonance (MR) image shows a well-circumscribed extraconal mass (arrowhead) superior to the ocular globe and isointense relative to muscle. (b) Another sagittal MR image shows that the mass is separate from the superior rectus muscle (arrow). (c) On the axial T2-weighted image, the mass is heterogeneous in signal intensity and predominantly hyperintense relative to gray matter and muscle. (d) Coronal T1-weighted image obtained after intravenous administration of gadolinium-based contrast material reveals intense enhancement of the tumor. (e) Photograph of the gross specimen shows it to be a well-circumscribed, fleshy tumor. Scale is in centimeters. (f) Photomicrograph (original magnification x200; hematoxylin-eosin [H-E] stain) shows pleomorphic (spindle-shaped and round) rhabdomyosarcomatous cells arranged in an alveolar pattern within a collagenized stroma. (g) Higher power photomicrograph (original magnification x400; H-E stain) of the same tumor specimen but from another area shows neoplastic cells with hyperchromatic, pleomorphic nuclei and scant cytoplasm distributed through a myxoid matrix. Fibrillary structures suggestive of cross striations may be seen in rare cells that have more ample cytoplasm and vesicular nuclei (straight arrow). Note numerous mitotic figures (arrowheads) and occasional pyknotic nuclei (tailed arrow).

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   Figure 1f.  Embryonal rhabdomyosarcoma with alveolar features in an 18-year-old boy with left proptosis. (a) Sagittal T1-weighted magnetic resonance (MR) image shows a well-circumscribed extraconal mass (arrowhead) superior to the ocular globe and isointense relative to muscle. (b) Another sagittal MR image shows that the mass is separate from the superior rectus muscle (arrow). (c) On the axial T2-weighted image, the mass is heterogeneous in signal intensity and predominantly hyperintense relative to gray matter and muscle. (d) Coronal T1-weighted image obtained after intravenous administration of gadolinium-based contrast material reveals intense enhancement of the tumor. (e) Photograph of the gross specimen shows it to be a well-circumscribed, fleshy tumor. Scale is in centimeters. (f) Photomicrograph (original magnification x200; hematoxylin-eosin [H-E] stain) shows pleomorphic (spindle-shaped and round) rhabdomyosarcomatous cells arranged in an alveolar pattern within a collagenized stroma. (g) Higher power photomicrograph (original magnification x400; H-E stain) of the same tumor specimen but from another area shows neoplastic cells with hyperchromatic, pleomorphic nuclei and scant cytoplasm distributed through a myxoid matrix. Fibrillary structures suggestive of cross striations may be seen in rare cells that have more ample cytoplasm and vesicular nuclei (straight arrow). Note numerous mitotic figures (arrowheads) and occasional pyknotic nuclei (tailed arrow).

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   Figure 1g.  Embryonal rhabdomyosarcoma with alveolar features in an 18-year-old boy with left proptosis. (a) Sagittal T1-weighted magnetic resonance (MR) image shows a well-circumscribed extraconal mass (arrowhead) superior to the ocular globe and isointense relative to muscle. (b) Another sagittal MR image shows that the mass is separate from the superior rectus muscle (arrow). (c) On the axial T2-weighted image, the mass is heterogeneous in signal intensity and predominantly hyperintense relative to gray matter and muscle. (d) Coronal T1-weighted image obtained after intravenous administration of gadolinium-based contrast material reveals intense enhancement of the tumor. (e) Photograph of the gross specimen shows it to be a well-circumscribed, fleshy tumor. Scale is in centimeters. (f) Photomicrograph (original magnification x200; hematoxylin-eosin [H-E] stain) shows pleomorphic (spindle-shaped and round) rhabdomyosarcomatous cells arranged in an alveolar pattern within a collagenized stroma. (g) Higher power photomicrograph (original magnification x400; H-E stain) of the same tumor specimen but from another area shows neoplastic cells with hyperchromatic, pleomorphic nuclei and scant cytoplasm distributed through a myxoid matrix. Fibrillary structures suggestive of cross striations may be seen in rare cells that have more ample cytoplasm and vesicular nuclei (straight arrow). Note numerous mitotic figures (arrowheads) and occasional pyknotic nuclei (tailed arrow).

The embryonal type is composed of elongate or spindle-shaped cells of various degrees of differentiation. These cells often have abundant eosinophilic cytoplasm and central hyperchromatic nuclei arranged in a herringbone pattern of interlacing fascicles (Fig 1f). Bipolar cells with tapered cytoplasmic processes are frequently seen; cells with long eosinophilic cytoplasmic extensions that resemble tadpoles are less common. Cross striations within the cytoplasm may be visible with Masson trichrome or phosphotungstic acid–hematoxylin stains in 60% of tumors (Fig 1g). These striations are formed by bundles of actin and myosin filaments and suggest a specific diagnosis of skeletal muscle differentiation. The surrounding stroma is often loose and myxoid (4).

The less common alveolar type is characterized by thin fibrovascular septa that separate the tumor into round to ovoid spaces (Fig 1f). Tumor cells are large, round to polygonal cells with abundant eosinophilic cytoplasm. The nuclei are large and vesicular. These cells loosely adhere to the thin connective tissue septa that surround relatively empty spaces in an arrangement reminiscent of alveoli in the lung (4).

Local Spread and Metastases
Rhabdomyosarcoma grows rapidly and behaves aggressively, frequently invading adjacent bones and soft tissues (Fig 2). However, advanced disease is less often encountered today because of greater awareness of the diagnosis.

View larger version (110K): [in this window] [in a new window] [Download PPT slide]   Figure 2a.  Rhabdomyosarcoma involving the orbit and maxillary sinus in an 18-year-old girl with erythema of the right lower eyelid followed by proptosis 2 months later. (a) Unenhanced coronal computed tomographic (CT) image (soft-tissue window) demonstrates a large, irregular soft-tissue mass in the maxillary sinus and inferior orbit that is iso- to slightly hyperattenuating relative to muscle. There is marked destruction of the bony orbital floor (arrowhead). (b) Same image, shown with a bone window level, better depicts the bone destruction (arrowhead).

View larger version (94K): [in this window] [in a new window] [Download PPT slide]   Figure 2b.  Rhabdomyosarcoma involving the orbit and maxillary sinus in an 18-year-old girl with erythema of the right lower eyelid followed by proptosis 2 months later. (a) Unenhanced coronal computed tomographic (CT) image (soft-tissue window) demonstrates a large, irregular soft-tissue mass in the maxillary sinus and inferior orbit that is iso- to slightly hyperattenuating relative to muscle. There is marked destruction of the bony orbital floor (arrowhead). (b) Same image, shown with a bone window level, better depicts the bone destruction (arrowhead).

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 3a.  Rhabdomyosarcoma in a 4-year-old boy with sickle cell anemia. (a) Coronal T1-weighted image shows a mass that is isointense relative to white matter involving the medial left orbit and the adjacent epidural space of the anterior cranial fossa (arrowhead). (b) Coronal T2-weighted MR image demonstrates hyperintense, left retropharyngeal (arrow) and left cervical (arrowhead) lymph nodes. Biopsy specimens from the latter revealed rhabdomyosarcoma. (c) Axial CT image shows soft tissue in the left maxillary sinus and periosteal reaction of the anterior wall of the sinus (arrow).

View larger version (133K): [in this window] [in a new window] [Download PPT slide]   Figure 3b.  Rhabdomyosarcoma in a 4-year-old boy with sickle cell anemia. (a) Coronal T1-weighted image shows a mass that is isointense relative to white matter involving the medial left orbit and the adjacent epidural space of the anterior cranial fossa (arrowhead). (b) Coronal T2-weighted MR image demonstrates hyperintense, left retropharyngeal (arrow) and left cervical (arrowhead) lymph nodes. Biopsy specimens from the latter revealed rhabdomyosarcoma. (c) Axial CT image shows soft tissue in the left maxillary sinus and periosteal reaction of the anterior wall of the sinus (arrow).

View larger version (135K): [in this window] [in a new window] [Download PPT slide]   Figure 3c.  Rhabdomyosarcoma in a 4-year-old boy with sickle cell anemia. (a) Coronal T1-weighted image shows a mass that is isointense relative to white matter involving the medial left orbit and the adjacent epidural space of the anterior cranial fossa (arrowhead). (b) Coronal T2-weighted MR image demonstrates hyperintense, left retropharyngeal (arrow) and left cervical (arrowhead) lymph nodes. Biopsy specimens from the latter revealed rhabdomyosarcoma. (c) Axial CT image shows soft tissue in the left maxillary sinus and periosteal reaction of the anterior wall of the sinus (arrow).

CT and MR imaging play important roles in the preoperative evaluation, staging, and follow-up of orbital rhabdomyosarcomas; are well suited to showing the aggressive behavior of these tumors, and can provide complementary information. CT is particularly suited for showing bone involvement (Figs 2, 3c), and MR imaging is sensitive for depicting intracranial extension (Fig 3). Serial follow-up CT may show healing or worsening of bone involvement, indicating the degree of response to treatment, and residual or recurrent disease may be observed with MR imaging (8,14). A worse prognosis is associated with residual disease after treatment.

On CT images, orbital rhabdomyosarcoma generally appears as an extraconal, irregular ovoid, well-circumscribed, homogeneous mass that is isoattenuated relative to muscle (Fig 2a). Calcification is usually seen only in association with destruction of adjacent bone (Fig 3c) (10). Larger tumors have less well-defined margins. Necrosis and hemorrhage are uncommon findings, but tumors with these features are heterogeneous. Eyelid thickening is a typical finding, whether or not the tumor extends to the eyelid (Fig 4) (10). Moderate to marked, generalized enhancement is seen on images obtained after intravenous injection of contrast material. Infrequently, the mass may be cavitary with ringlike enhancement (Fig 4) (1). The mass often appears contiguous with adjacent extraocular muscles, but the muscles are displaced or encased, with no enlargement of the muscle belly (Fig 1) (8,10). At CT, the tumor can be seen to erode or thin bone in about 40% of patients, particularly those with large tumors (Figs 2, 3c) (1,8,10).

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   Figure 4a.  Embryonal rhabdomyosarcoma in a 4-year-old girl with right proptosis. (a) Axial T1-weighted MR image demonstrates a well-defined mass that is iso- to slightly hypointense relative to muscle (arrowhead). Note the swelling of the upper eyelid. (b) Axial T1-weighted image with fat saturation shows intense, rimlike enhancement (arrowhead) of the mass and overlying lid.

View larger version (139K): [in this window] [in a new window] [Download PPT slide]   Figure 4b.  Embryonal rhabdomyosarcoma in a 4-year-old girl with right proptosis. (a) Axial T1-weighted MR image demonstrates a well-defined mass that is iso- to slightly hypointense relative to muscle (arrowhead). Note the swelling of the upper eyelid. (b) Axial T1-weighted image with fat saturation shows intense, rimlike enhancement (arrowhead) of the mass and overlying lid.

View larger version (92K): [in this window] [in a new window] [Download PPT slide]   Figure 5a.  Rhabdomyosarcoma with imaging features mimicking those of hemangioma in a 4-year-old boy with right eye pain and proptosis. (a) Axial CT image shows a mass isoattenuating relative to muscle with a lobular contour suggestive of hemangioma. (b) Coronal short inversion time inversion-recovery image reveals the hyperintense mass, which contains serpentine dark flow void (arrow). Note the ill-defined inferior tumor margin (arrowhead). (c) Sagittal T2-weighted image shows another flow void (arrow), mimicking the features of hemangioma. (d) Coronal T1-weighted image with fat saturation shows somewhat heterogeneous enhancement, which is more characteristic of rhabdomyosarcoma than hemangioma. Note the encased optic nerve (arrowhead). Because the imaging features are nondiagnostic and because the patient age is inconsistent with hemangioma, biopsy was performed to obtain the proper diagnosis.

View larger version (116K): [in this window] [in a new window] [Download PPT slide]   Figure 5b.  Rhabdomyosarcoma with imaging features mimicking those of hemangioma in a 4-year-old boy with right eye pain and proptosis. (a) Axial CT image shows a mass isoattenuating relative to muscle with a lobular contour suggestive of hemangioma. (b) Coronal short inversion time inversion-recovery image reveals the hyperintense mass, which contains serpentine dark flow void (arrow). Note the ill-defined inferior tumor margin (arrowhead). (c) Sagittal T2-weighted image shows another flow void (arrow), mimicking the features of hemangioma. (d) Coronal T1-weighted image with fat saturation shows somewhat heterogeneous enhancement, which is more characteristic of rhabdomyosarcoma than hemangioma. Note the encased optic nerve (arrowhead). Because the imaging features are nondiagnostic and because the patient age is inconsistent with hemangioma, biopsy was performed to obtain the proper diagnosis.

View larger version (129K): [in this window] [in a new window] [Download PPT slide]   Figure 5c.  Rhabdomyosarcoma with imaging features mimicking those of hemangioma in a 4-year-old boy with right eye pain and proptosis. (a) Axial CT image shows a mass isoattenuating relative to muscle with a lobular contour suggestive of hemangioma. (b) Coronal short inversion time inversion-recovery image reveals the hyperintense mass, which contains serpentine dark flow void (arrow). Note the ill-defined inferior tumor margin (arrowhead). (c) Sagittal T2-weighted image shows another flow void (arrow), mimicking the features of hemangioma. (d) Coronal T1-weighted image with fat saturation shows somewhat heterogeneous enhancement, which is more characteristic of rhabdomyosarcoma than hemangioma. Note the encased optic nerve (arrowhead). Because the imaging features are nondiagnostic and because the patient age is inconsistent with hemangioma, biopsy was performed to obtain the proper diagnosis.

View larger version (115K): [in this window] [in a new window] [Download PPT slide]   Figure 5d.  Rhabdomyosarcoma with imaging features mimicking those of hemangioma in a 4-year-old boy with right eye pain and proptosis. (a) Axial CT image shows a mass isoattenuating relative to muscle with a lobular contour suggestive of hemangioma. (b) Coronal short inversion time inversion-recovery image reveals the hyperintense mass, which contains serpentine dark flow void (arrow). Note the ill-defined inferior tumor margin (arrowhead). (c) Sagittal T2-weighted image shows another flow void (arrow), mimicking the features of hemangioma. (d) Coronal T1-weighted image with fat saturation shows somewhat heterogeneous enhancement, which is more characteristic of rhabdomyosarcoma than hemangioma. Note the encased optic nerve (arrowhead). Because the imaging features are nondiagnostic and because the patient age is inconsistent with hemangioma, biopsy was performed to obtain the proper diagnosis.

Subperiosteal hemorrhage caused by trauma may mimic the appearance of rhabdomyosarcoma, especially on CT scans, since it causes erosive changes in bone as it resolves. In rare cases, a patient may present with trauma and a previously unknown rhabdomyosarcoma, and the imaging findings may be incorrectly attributed to the trauma (9). MR imaging may be helpful in demonstrating the changing signal intensity of evolving blood products, which are infrequently found within rhabdomyosarcoma.

Orbital cellulitis with abscess (Fig 6), similar to rhabdomyosarcoma, commonly manifests with rapid onset of eyelid swelling and proptosis. Both conditions may also show imaging findings of an orbital mass and adjacent paranasal sinus involvement. Contrast-enhanced MR images can be helpful for distinguishing sinus secretions from enhancing tumor that involves the paranasal sinus. Infrequently, rhabdomyosarcoma may appear as a ring-enhancing mass, an appearance similar to that of an abscess. Additional clinical findings of fever and leukocytosis and the finding of inflammatory changes in the orbital fat on CT images suggest the diagnosis of infection. In addition, orbital cellulitis is much more common than rhabdomyosarcoma (3,9,10).

View larger version (100K): [in this window] [in a new window] [Download PPT slide]   Figure 6a.  Orbital cellulitis in a 5-year-old boy with periorbital erythema. (a) Axial CT image shows increased attenuation in the preseptal and postseptal fat, a finding consistent with inflammation. Note the soft-tissue opacification of the ethmoid air cells and sphenoid sinus. (b) Coronal contrast-enhanced CT image shows a subperiosteal abscess (arrowhead) along the lamina papyracea. The rim enhancement seen here is rare in rhabdomyosarcoma.

View larger version (94K): [in this window] [in a new window] [Download PPT slide]   Figure 6b.  Orbital cellulitis in a 5-year-old boy with periorbital erythema. (a) Axial CT image shows increased attenuation in the preseptal and postseptal fat, a finding consistent with inflammation. Note the soft-tissue opacification of the ethmoid air cells and sphenoid sinus. (b) Coronal contrast-enhanced CT image shows a subperiosteal abscess (arrowhead) along the lamina papyracea. The rim enhancement seen here is rare in rhabdomyosarcoma.

Vasculogenic tumors may occur in the orbit in young children and may appear similar to rhabdomyosarcoma. Capillary hemangioma (discussed in another section) is a benign neoplasm with abnormal proliferation of endothelial cells. This tumor occurs in younger patients than does rhabdomyosarcoma, since it usually manifests in the first few months of life, but in rare cases rhabdomyosarcoma may develop in patients as young as newborns. Capillary hemangiomas grow in the first 12–18 months of life, a trait that could suggest a malignant tumor. Hemangiomas are very vascular masses, and use of dynamic contrast-enhanced CT or MR imaging can be very helpful in demonstrating their vascular nature. MR imaging may demonstrate peripheral and internal flow voids, findings that are characteristic of the high-flow hemangioma; however, in rare cases, rhabdomyosarcoma can also be hypervascular (Fig 5). The associated finding of ipsilateral cutaneous hemangiomas in some patients may suggest the proper diagnosis.

Vascular malformations may also occur in the orbit and occasionally simulate the appearance of a malignant tumor. These lesions (discussed in another section) generally contain lymphatic and venous components. They occur in the same age group as does rhabdomyosarcoma and often come to clinical attention because of the rapid onset of proptosis (due to internal hemorrhage or infection), characteristics that suggest the diagnosis of rhabdomyosarcoma (6). On images, vascular malformations are often cystic and multiloculated with ill-defined borders. They frequently contain fluid-fluid levels because of hemorrhage into the cysts, whereas fluid-fluid levels are quite uncommon in rhabdomyosarcoma. Large cystic spaces of lymphatic components do not enhance centrally, although their walls may show peripheral enhancement. Peripheral enhancement is uncommon in rhabdomyosarcoma (Fig 4). The venous components may contain phleboliths, which help distinguish the malformation from rhabdomyosarcoma.

Langerhans cell histiocytosis is a histiocytic lesion that behaves aggressively in children. Orbital involvement occurs in 23% of children with LCH and always involves the bone, since it originates in bone and spreads directly into the orbit. Thus, orbital Langerhans cell histiocytosis can simulate the imaging appearance of rhabdomyosarcoma with bone invasion, although bone destruction in the former is typically more pronounced (16). Both of these entities may spread into adjacent paranasal sinuses or intracranial contents. The unusual clinical finding of diabetes insipidus due to involvement of the infundibulum or the presence of additional bone lesions suggests Langerhans cell histiocytosis, although rhabdomyosarcoma may metastasize to bone as well.

Leukemia and lymphoma account for 10% of orbital tumors (9). The two diseases that most frequently involve the orbit are granulocytic sarcoma (chloroma), which usually occurs in myelogenous leukemia in younger children, and non-Hodgkin lymphoma (NHL) in older children. Chloromas may be bilateral, whereas rhabdomyosarcoma is always unilateral. Analysis of a peripheral blood smear may help suggest the diagnosis of leukemia if it is not already known. Biopsy is usually necessary to reliably distinguish between the two.

Orbital lymphoma can be primary or secondary to systemic lymphoma, and NHL is most likely to affect the orbit. Although NHL is usually found in older adults, it can occur in older children or adolescents. Unlike rhabdomyosarcoma, NHL commonly causes lacrimal gland involvement, may be hypointense on T2-weighted images, and encases rather than distorts the globe (17).

Neuroblastoma metastases to the orbit are not rare and may simulate the appearance of rhabdomyosarcoma with bone involvement. The finding of a primary tumor in the retroperitoneum or posterior mediastinum would suggest the proper diagnosis of neuroblastoma (9).

Treatment and Prognosis
CT or MR imaging is useful in tumor staging, which has important treatment and prognostic implications. The orbital rhabdomyosarcoma is assigned to one of four groups, as defined by the Intergroup Rhabdomyosarcoma Study Group. In general, group I tumors are localized and can be completely resected. Group II tumors have only residual microscopic disease after surgery. The group III designation is reserved for tumors with gross residual disease after biopsy. Group IV tumors have distant metastases at onset (7). Most orbital tumors (48%) are group III (4).

Open biopsy is preferred over fine-needle aspiration, especially for posterior tumors, as the latter may yield inadequate or even misleading information (6,14).

Until the early 1970s, the treatment for orbital rhabdomyosarcoma was exenteration, yet the prognosis for these patients was poor, with a 5-year survival rate of about 20%. For this reason, the Intergroup Rhabdomyosarcoma Study Group was formed. As a result, the treatment now consists of incisional or excisional biopsy or surgical debulking, followed by radiation therapy and chemotherapy. The 5-year survival rate for orbital rhabdomyosarcoma is now greater than 90%, compared with the 5-year survival rate of 70% for all primary sites of rhabdomyosarcoma (1,4). The survival rate for the embryonal type is 94%, but the alveolar form has a worse prognosis, with 5-year survival rate of 74% (1). With long-term survival now expected, new refinements in therapy are being directed toward preserving sight and preventing complications of therapy, such as secondary malignancies.

Favorable prognostic factors include lack of distant metastases, primary site in the orbit, disease confined to the orbit, grossly complete surgical resection, patient age less than 10 years, embryonal histologic type, hyperdiploid DNA content, and tumor of 5 cm or less in size. The most important prognostic factor is response to therapy, which is determined with follow-up imaging (4,6).

	Vasculogenic Lesions

Top Abstract LEARNING OBJECTIVES FOR TEST... Introduction Rhabdomyosarcoma Vasculogenic Lesions Infantile Fibromatosis Summary References

 
Vascular lesions account for 5%–20% of orbital masses (18), and hemangioma and lymphangioma are the most common vascular lesions in the orbit (19,20). Much controversy exists regarding the nomenclature and classification of these lesions. The term hemangioma has been widely and inappropriately applied to a number of varied lesions, a practice that has led to clinical confusion and inappropriate, possibly harmful treatment. According to the biologically based classification system initially proposed by Mulliken and Glowacki (21), the term hemangioma should be reserved for true neoplasms with vascular channels lined by proliferating endothelial cells. Such tumors occur in newborns shortly after birth and then undergo a proliferative phase of growth; an involutional phase starts at about 1 year of age and lasts for several years. These tumors may also be called infantile hemangiomas or capillary hemangiomas. If they involve the skin, they can be diagnosed on the basis of clinical appearance. Deeper lesions are recognized by the presence of large, high-flow vessels within and at the periphery of the mass (22,23).

Other vascular lesions (some previously called hemangiomas) are not neoplasms but rather developmental anomalies and should be designated malformations. These malformations consist of vascular channels of varied size and histologic type, lined by nonproliferating endothelial cells. The lesions are formed of collections of abnormally dilated arteries, veins, capillaries, or lymphatic vessels. They may be subdivided on the basis of hemodynamic characteristics into high-and low-flow lesions. High-flow lesions contain arterial vessels, and most commonly such lesions are arteriovenous malformations, which have bruits and thrills at clinical examination. Low-flow lesions contain veins, capillaries, or lymphatic vessels. Unlike hemangiomas, vascular malformations grow commensurate with the growth of the patient and never spontaneously involute (22,23).

Infantile Hemangioma
Infantile hemangioma is the most common tumor of infancy. Sixty percent of these tumors occur in the head and neck (4,24). Shields et al (3), in a study of 1264 patients referred to a multidisciplinary specialty center, found that hemangiomas represented 3% of all orbital lesions and 17% of vasculogenic lesions of the orbit.

Epidemiology and Clinical Features.— Hemangioma has no known familial or hereditary association. There is a slight female predilection, with a female-to-male ratio of 3:2 (19,25). The tumor may be present at birth as a reddish macule, but in most cases the tumor becomes apparent within the first few weeks to months of life. Almost all cases are diagnosed within the first 6 months of life. Hemangiomas then enter a proliferative phase, which lasts up to 10 months after diagnosis, followed by a short period of stabilization and then a prolonged period of slow involution, which may last as long as 7–10 years (21, 23,25).

When hemangiomas involve the skin, they cause a lobulated contour and a bright red to bluish-red discoloration that resembles the surface of a strawberry and is clinically diagnostic. Deeper hemangiomas may have a blue hue, or the overlying skin may appear normal. These tumors usually require radiologic evaluation for diagnosis. At palpation, superficial hemangiomas are usually warm and may be pulsatile (20,23).

The majority of hemangiomas that involve the orbital region are anterior, but occasionally they are found in the retro-ocular portions of the orbit. The most frequent appearance of a hemangioma in the periorbital region is a strawberry lesion involving the eyelid. Patients with deeper lesions develop proptosis in early infancy. Complications may ensue as the mass enlarges, including amblyopia, visual axis occlusion, stretching of the optic nerve, bleeding, and corneal ulceration (4,25,26).

Almost one-third of patients with orbital hemangiomas have additional lesions in the skin or viscera (25). Visceral lesions, if large or numerous, can cause the complication of high-output heart failure. More aggressive histologic variants of hemangioma can also cause a severe consumptive thrombocytopenic coagulopathy called Kasabach-Merritt syndrome. Some orbital hemangiomas may be associated with cerebral and vascular anomalies known as PHACES syndrome, which is an acronym encompassing posterior fossa anomalies, hemangiomas of the face, arterial abnormalities (including coarctation of the aorta), cerebral vascular anomalies, eye abnormalities, and sternal or ventral developmental anomalies (23).

Pathologic Features.— At gross examination, hemangiomas are vascular and multilobular (Fig 7c, 7d). At histologic analysis, the tumor growth appears infiltrative and may involve adjacent orbital structures. In the early proliferative phase, the lesion is composed of densely packed, plump, hyperplastic endothelial cells that form clusters or lobules (Fig 8c). Within these lobules are very small capillary-sized vascular spaces with inconspicuous lumina (Fig 8d). The endothelial cells may show numerous mitotic figures. The lobules are separated by fibrous septa, which convey the feeding vessels and draining veins. During the involutional phase, the endothelial cells become flatter and more mature, and the vascular lumina become more conspicuous. There is progressive replacement of the cellular lobules with fibrofatty tissue (Fig 9). Involution begins in the center and then proceeds peripherally. In the final involuted phase, the cellular component is completely replaced with fibrosis and fat and the vasculature has atrophied (4,27).

View larger version (146K): [in this window] [in a new window] [Download PPT slide]   Figure 7a.  Infantile hemangioma in a 2-month-old infant who was noted to have a mass in the left temporal area shortly after birth. (a) Coronal T2-weighted image shows a mass slightly hyperintense relative to muscle and brain that contains numerous black flow voids (arrowheads). (b) Axial T2-weighted image shows that the mass extends into the temporal region. Note the prominent intratumoral flow voids (arrowhead). (c) Photograph of the gross specimen reveals a red, hemorrhagic tumor with circumscribed borders. Scale is in centimeters. (d) Photograph of the gross specimen from another patient with a capillary hemangioma of the scalp shows a red, vascular mass with lobulated contour.

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   Figure 7b.  Infantile hemangioma in a 2-month-old infant who was noted to have a mass in the left temporal area shortly after birth. (a) Coronal T2-weighted image shows a mass slightly hyperintense relative to muscle and brain that contains numerous black flow voids (arrowheads). (b) Axial T2-weighted image shows that the mass extends into the temporal region. Note the prominent intratumoral flow voids (arrowhead). (c) Photograph of the gross specimen reveals a red, hemorrhagic tumor with circumscribed borders. Scale is in centimeters. (d) Photograph of the gross specimen from another patient with a capillary hemangioma of the scalp shows a red, vascular mass with lobulated contour.

View larger version (90K): [in this window] [in a new window] [Download PPT slide]   Figure 7c.  Infantile hemangioma in a 2-month-old infant who was noted to have a mass in the left temporal area shortly after birth. (a) Coronal T2-weighted image shows a mass slightly hyperintense relative to muscle and brain that contains numerous black flow voids (arrowheads). (b) Axial T2-weighted image shows that the mass extends into the temporal region. Note the prominent intratumoral flow voids (arrowhead). (c) Photograph of the gross specimen reveals a red, hemorrhagic tumor with circumscribed borders. Scale is in centimeters. (d) Photograph of the gross specimen from another patient with a capillary hemangioma of the scalp shows a red, vascular mass with lobulated contour.

View larger version (94K): [in this window] [in a new window] [Download PPT slide]   Figure 7d.  Infantile hemangioma in a 2-month-old infant who was noted to have a mass in the left temporal area shortly after birth. (a) Coronal T2-weighted image shows a mass slightly hyperintense relative to muscle and brain that contains numerous black flow voids (arrowheads). (b) Axial T2-weighted image shows that the mass extends into the temporal region. Note the prominent intratumoral flow voids (arrowhead). (c) Photograph of the gross specimen reveals a red, hemorrhagic tumor with circumscribed borders. Scale is in centimeters. (d) Photograph of the gross specimen from another patient with a capillary hemangioma of the scalp shows a red, vascular mass with lobulated contour.

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 8a.  Capillary hemangioma in an 8-week-old girl with a 2-week history of left proptosis. (a, b) Axial contrast-enhanced CT images (a obtained at a lower level than b) show an intensely enhancing intraconal mass in the left orbit. (c) Photomicrograph (original magnification x100; H-E stain) demonstrates well-circumscribed lobules of neoplastic cells (*). (d) Photomicrograph (original magnification x400; H-E stain) shows small vascular spaces (arrowheads) surrounded by spindle-shaped stromal cells.

View larger version (119K): [in this window] [in a new window] [Download PPT slide]   Figure 8b.  Capillary hemangioma in an 8-week-old girl with a 2-week history of left proptosis. (a, b) Axial contrast-enhanced CT images (a obtained at a lower level than b) show an intensely enhancing intraconal mass in the left orbit. (c) Photomicrograph (original magnification x100; H-E stain) demonstrates well-circumscribed lobules of neoplastic cells (*). (d) Photomicrograph (original magnification x400; H-E stain) shows small vascular spaces (arrowheads) surrounded by spindle-shaped stromal cells.

View larger version (187K): [in this window] [in a new window] [Download PPT slide]   Figure 8c.  Capillary hemangioma in an 8-week-old girl with a 2-week history of left proptosis. (a, b) Axial contrast-enhanced CT images (a obtained at a lower level than b) show an intensely enhancing intraconal mass in the left orbit. (c) Photomicrograph (original magnification x100; H-E stain) demonstrates well-circumscribed lobules of neoplastic cells (*). (d) Photomicrograph (original magnification x400; H-E stain) shows small vascular spaces (arrowheads) surrounded by spindle-shaped stromal cells.

View larger version (168K): [in this window] [in a new window] [Download PPT slide]   Figure 8d.  Capillary hemangioma in an 8-week-old girl with a 2-week history of left proptosis. (a, b) Axial contrast-enhanced CT images (a obtained at a lower level than b) show an intensely enhancing intraconal mass in the left orbit. (c) Photomicrograph (original magnification x100; H-E stain) demonstrates well-circumscribed lobules of neoplastic cells (*). (d) Photomicrograph (original magnification x400; H-E stain) shows small vascular spaces (arrowheads) surrounded by spindle-shaped stromal cells.

View larger version (195K): [in this window] [in a new window] [Download PPT slide]   Figure 9.  Involuting hemangioma in a 5-week-old girl born with a large right orbital mass. Photomicrograph (original magnification x100; H-E stain) reveals that the stroma is more collagenized (*) between the islands of neoplastic cells than is seen in less mature lobular capillary hemangiomas (cf Fig 8).

US performed by an experienced practitioner is useful for evaluation of suspected vasculogenic lesions and for their follow-up. In the proliferative phase, the hemangioma is smoothly contoured and of variable echogenicity, usually hyperechoic. Doppler imaging demonstrates marked intralesional flow, high density of vessels (more than five vessels per square centimeter), increased arterial and venous flow velocity (Doppler shift > 2 kHz), and low resistance arterial flow (24). During the involutional phase, the size and number of vessels in the lesion decline (12,13,23,24,28).

CT is better suited than US for showing the full extent of hemangiomas, but it lacks the superior soft-tissue resolution of MR imaging. Large lesions may expand the bony orbit, and smaller lesions may cause scalloping. Invasion of bone is extremely rare. The mass is most commonly extraconal. In the proliferative phase, the mass is fairly homogeneous and isoattenuated relative to muscle, although the attenuation may be higher than that of normal brain tissue due to blood in the vascular spaces. Calcifications are rare. After intravenous administration of contrast material, the tumor enhances promptly, markedly, uniformly, and persistently (Fig 8a). The lobulated contour is more evident with contrast material (Fig 10b). The lesions are usually well demarcated but may have indistinct margins. During involution, the lesion is progressively replaced by fat, which is well demonstrated on CT scans. The mass becomes more heterogeneous and enhances less (19,23,24,26).

View larger version (97K): [in this window] [in a new window] [Download PPT slide]   Figure 10a.  Capillary hemangioma in a 9-week-old girl with right exophthalmos. (a) Axial T1-weighted image shows the lobular contour of an intraconal mass (arrowhead) with signal intensity similar to that of muscle and contrasted against the hyperintense conal fat. (b) Axial contrast-enhanced T1-weighted image with fat saturation demonstrates diffuse intense enhancement of the lobular mass. (c) Sagittal T2-weighted image also shows the hyperintense mass, which contains flow voids (arrowhead).

View larger version (101K): [in this window] [in a new window] [Download PPT slide]   Figure 10b.  Capillary hemangioma in a 9-week-old girl with right exophthalmos. (a) Axial T1-weighted image shows the lobular contour of an intraconal mass (arrowhead) with signal intensity similar to that of muscle and contrasted against the hyperintense conal fat. (b) Axial contrast-enhanced T1-weighted image with fat saturation demonstrates diffuse intense enhancement of the lobular mass. (c) Sagittal T2-weighted image also shows the hyperintense mass, which contains flow voids (arrowhead).

View larger version (113K): [in this window] [in a new window] [Download PPT slide]   Figure 10c.  Capillary hemangioma in a 9-week-old girl with right exophthalmos. (a) Axial T1-weighted image shows the lobular contour of an intraconal mass (arrowhead) with signal intensity similar to that of muscle and contrasted against the hyperintense conal fat. (b) Axial contrast-enhanced T1-weighted image with fat saturation demonstrates diffuse intense enhancement of the lobular mass. (c) Sagittal T2-weighted image also shows the hyperintense mass, which contains flow voids (arrowhead).