(Radiographics. 1999;19:241-244.)
© RSNA, 1999
Pediatric Case of the Day
Robert J. Coombs, MD1,
Emel A. Bayar, MD2,
Yousif H. Matloub, MD2 and
Manuel E. Velasco, MD3
1 Departments of Radiology (R.J.C.)
2 Pediatrics (E.B., Y.H.M.)
3 Pathology (M.E.V.), Medical College of Ohio, 3000 Arlington Ave, Toledo, OH 43614-2598.
Index Terms: Ewing sarcoma, 471.3281 • Neoplasms, in infants and children, 471.3281 • Ribs, neoplasms, 471.3281 • Spinal canal, neoplasms, 351.37
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HISTORY
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A previously healthy 11-year-old boy presented at our institution with a 2-month history of intermittent upper back pain that had been progressively worsening over the past week. The patient also complained of a mass causing a bulge on his upper back, accompanying chest pains, and numbness in both legs. Radiography, computed tomography (CT), and magnetic resonance (MR) imaging were performed.
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FINDINGS
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Radiography revealed an expansile tumor originating from the left posterior fifth rib and subtly displacing the fourth rib superiorly (Fig 1a). The mass was accompanied by a larger, surrounding soft-tissue mass that was seen to extend into the thoracic cavity (Fig 1b). CT of this lesion showed a densely calcified expansile lesion of the fifth rib with a spiculated anterior margin (Fig 2). A surrounding soft-tissue component was easily seen anteriorly but blended imperceptibly with the muscle posteriorly. In addition, a soft-tissue component could be seen entering through the intervertebral foramen and causing considerable anterior and rightward displacement of the spinal cord, which was markedly compressed. Axial T2-weighted gradient-echo MR images showed the tumor with high signal intensity displacing the spinal cord toward the right and anteriorly (Fig 3a) in a manner similar to that seen at CT. Sagittal T2-weighted spin-echo MR images of the thoracic spine clearly demonstrated the cranial and caudal extent of the tumor (Fig 3b). The marked compression of the spinal cord at the site of the tumor was clearly distinguishable from the normal anteroposterior diameter of the uninvolved spinal cord above and below the tumor.
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Figure 1a. (a) Posteroanterior chest radiograph shows an expansile sclerotic lesion involving the left fifth rib. (b) Lateral chest radiograph shows an intrathoracic soft-tissue component.
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Figure 1b. (a) Posteroanterior chest radiograph shows an expansile sclerotic lesion involving the left fifth rib. (b) Lateral chest radiograph shows an intrathoracic soft-tissue component.
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Figure 2. Figures 2, 3. (2) CT scan shows dense bone at the center of the tumor with bony spiculation primarily along the anterior margin. The soft-tissue component of the tumor extends through the vertebral foramen, displacing and compressing the spinal cord (arrow). R = right side of patient. (3a) Axial T2-weighted gradient-echo MR image (repetition time msec/echo time msec = 644/27; 25° flip angle) demonstrates the high-signal-intensity tumor within the spinal canal. The tumor is seen displacing and compressing the spinal cord, which has lower signal intensity (arrow). The area of high signal intensity in the soft tissue represents posterior extension of the tumor not seen at CT (cf Fig 2). (3b) Sagittal T2-weighted spin-echo MR image (2,700/120) clearly delineates the cranial and caudal extent of the tumor (arrows).
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Figure 3a. Figures 2, 3. (2) CT scan shows dense bone at the center of the tumor with bony spiculation primarily along the anterior margin. The soft-tissue component of the tumor extends through the vertebral foramen, displacing and compressing the spinal cord (arrow). R = right side of patient. (3a) Axial T2-weighted gradient-echo MR image (repetition time msec/echo time msec = 644/27; 25° flip angle) demonstrates the high-signal-intensity tumor within the spinal canal. The tumor is seen displacing and compressing the spinal cord, which has lower signal intensity (arrow). The area of high signal intensity in the soft tissue represents posterior extension of the tumor not seen at CT (cf Fig 2). (3b) Sagittal T2-weighted spin-echo MR image (2,700/120) clearly delineates the cranial and caudal extent of the tumor (arrows).
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Figure 3b. Figures 2, 3. (2) CT scan shows dense bone at the center of the tumor with bony spiculation primarily along the anterior margin. The soft-tissue component of the tumor extends through the vertebral foramen, displacing and compressing the spinal cord (arrow). R = right side of patient. (3a) Axial T2-weighted gradient-echo MR image (repetition time msec/echo time msec = 644/27; 25° flip angle) demonstrates the high-signal-intensity tumor within the spinal canal. The tumor is seen displacing and compressing the spinal cord, which has lower signal intensity (arrow). The area of high signal intensity in the soft tissue represents posterior extension of the tumor not seen at CT (cf Fig 2). (3b) Sagittal T2-weighted spin-echo MR image (2,700/120) clearly delineates the cranial and caudal extent of the tumor (arrows).
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DIAGNOSIS: Ewing sarcoma of the rib with intraspinal extension.
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DISCUSSION
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Ewing sarcoma is the fourth most common malignant bone tumor overall (1) and the second most common malignant bone tumor in pediatric patients (2). Most Ewing sarcomas occur in patients between 3 and 25 years of age (mean, 13 years) (3). Ewing tumors have a female predilection of approximately 2:1 (1). About 10% of Ewing tumors occur within the ribs (2,4).
Ewing sarcoma of the ribs has a propensity to spread inward toward the thoracic cavity. This extension may manifest as a strictly extrapleural mass pushing into the thoracic cavity (as in this case), or it may invade the thoracic cavity with direct invasion of deep structures (mediastinum, pericardium, diaphragm) (4). Ewing sarcoma in the posterior ribs can spread via the intervertebral foramina into the spinal canal (as in this case). This direct spread has been documented previously at CT in one case (4). Four cases of primitive neuroectodermal tumor, which is pathologically similar to Ewing sarcoma, have been documented extending into the spinal canal (5).
Malignant primary tumors of the chest wall have been reported as more common than benign primary chest wall tumors in children (6). Ewing sarcoma is the most common malignant chest wall tumor in childhood (6). Numerous benign chest wall tumors (eg, aneurysmal bone cyst, chondroblastoma, enchondroma, osteoblastoma, osteochondroma) have been documented in the literature (6,7). None of these tumors has occurred with great frequency. Benign rib tumors usually appear as cortical rib destruction with an associated soft-tissue mass. Benign tumors of the chest wall are more likely to occur with systemic syndromes (eg, neurofibromatosis, histiocytosis, osteochondromatosis) than as isolated findings (6).
If primitive neuroectodermal tumors are considered to be Ewing tumors, Ewing sarcoma is the most common malignant primary bone tumor of the chest wall. Chondrosarcomas and osteosarcomas of the ribs as primary malignancies are quite rare in pediatric patients (6). However, metastatic lesions to the ribs are common and should be considered in the differential diagnosis. These lesions occur mostly with neuroblastoma and leukemia (7). The tumor that most commonly shows extension between the chest wall and the spinal canal is neurofibroma or neurofibrosarcoma in the setting of neurofibromatosis (8).
The radiographic appearance of Ewing sarcoma in the rib cage is variable (1,4,6). The lesion may be primarily lytic or sclerotic or may represent a mixture of the two. In cases in which the sclerotic pattern predominates, finding the primary lesion should be quite easy. Occasionally, however, a lytic Ewing tumor can be obscured when associated with a large pleural effusion (6). In cases in which metastatic disease and systemic syndromes have been excluded, Ewing sarcoma should be strongly considered as part of the differential diagnosis in all rib lesions because it is by far the most common primary malignant lesion of the ribs. Other nonneoplastic entities such as osteomyelitis, unusual-appearing fracture, callus, and direct spread of lung infection into the chest wall can simulate the appearance of Ewing sarcoma (6).
CT is superior to radiography in evaluation for the presence of a lesion and characterization of a known lesion. The sclerotic or lytic character of the lesion as well as its spread toward the thoracic cavity should be perceived easily at CT. Furthermore, any associated pleural effusion should be easy to differentiate from the soft-tissue mass. Direct extension of Ewing sarcoma of the ribs into the epidural space of the spinal canal has been reported in one case (4). It can be somewhat difficult to visualize the entire extent of the tumor within the spinal canal at unenhanced CT; therefore, full evaluation of the intraspinal extent of a tumor requires intrathecal injection of contrast material if CT is the only modality being used.
With the advent of MR imaging, additional diagnostic information can be obtained prior to instituting definitive therapy. The intramuscular extent of the tumor into the chest wall can be evaluated more precisely with MR imaging than with CT because of the higher contrast between tumor and soft tissue it affords. Such an advantage would be valuable when surgical resection of the mass from the chest wall is being contemplated. In addition, spread of any tumor into the spinal canal can be evaluated with MR imaging without the use of intrathecal contrast material. Although axial MR imaging provides information similar to that provided by axial CT, the true craniocaudal extent of the tumor is more easily appreciated at MR imaging performed in the sagittal plane (as in this case).
Our patient underwent surgical excision of a fibrous mass from the left-sided paraspinal muscles. A laminectomy was performed from T4 to T6, and copious amounts of gelatinous intraspinal tumor that were compressing the spinal cord were removed from the epidural space. The patient remained neurologically intact after surgery.
Histologic analysis of the tumor (Fig 4) revealed dense sheets and tight clusters of small, uniform cells with inconspicuous cytoplasm and ill-defined borders (Fig 4a). Nuclei were round to oval and demonstrated sparse, finely stippled chromatin. Occasional cells with poorly defined glycogen lakes were observed. Numerous cells demonstrated strong cell surface immunoreactivity for MIC2, a marker consistently expressed by the cells in Ewing sarcoma (Fig 4b). The histologic appearance and strong MIC2 immunoreactivity of the tumor were essential in establishing the pathologic diagnosis.
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Figure 4a. (a) High-power photomicrograph (original magnification, x1,000; hematoxylin-eosin stain) shows a dense aggregate of small, uniform cells with poorly defined borders, inconspicuous cytoplasm, and round to oval nuclei. (b) High-power photomicrograph (original magnification, x1,000; immunoperoxidase stain) shows numerous cells with strong MIC2 immunoreactivity. The stain is localized mostly in the cell membranes.
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Figure 4b. (a) High-power photomicrograph (original magnification, x1,000; hematoxylin-eosin stain) shows a dense aggregate of small, uniform cells with poorly defined borders, inconspicuous cytoplasm, and round to oval nuclei. (b) High-power photomicrograph (original magnification, x1,000; immunoperoxidase stain) shows numerous cells with strong MIC2 immunoreactivity. The stain is localized mostly in the cell membranes.
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Once the diagnosis was made, a work-up for metastases was performed that included bone marrow aspiration and biopsy, CT of the abdomen, and a radionuclide bone scan. None of these procedures showed any evidence of distant metastatic lesions.
The patient underwent 30 weeks of chemotherapy that included courses of vincristine, cyclophosphamide, and doxorubicin alternating with courses of ifosfamide and etoposide. Radiation therapy consisted of 50.4 Gy administered over approximately 6 weeks. A very favorable response was achieved with this regimen, and the patient remains disease free 1 year after cessation of therapy.
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Acknowledgments
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The authors thank Pat Sams, Carol French for typing the manuscript, Randy Falor for providing the photographs, and the Department of Radiology at Defiance (Ohio) Hospital for providing the MR images.
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Footnotes
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Address reprint requests to R.J.C.
From the 1998 RSNA scientific assembly.
Received for publication September 8, 1998.
Revision received September 23, 1998. October 20, 1998.
Accepted for publication October 20, 1998.
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References
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Mirrha JM. Bone tumors: diagnosis and treatment Philadelphia, Pa: Lippincott, 1980; 419-422.
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Rao BN, Hayes FA, Thompson EI, et al. Chest wall resection for Ewing's sarcoma of the rib: an unnecessary procedure. Ann Thorac Surg 1995; 60:1454-1455.[Free Full Text]
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Ozaki T, Lindner N, Hoffmann C, et al. Ewing's sarcoma of the ribs: a report from the cooperative Ewing's sarcoma study. Eur J Cancer 1995; 31:2284-2288.
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Levine E, Levine C. Ewing tumor of rib: radiologic findings and computed tomography contribution. Skeletal Radiol 1983; 9:227-233.[Medline]
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Jürgens H, Bier V, Harms D, et al. Malignant peripheral neuroectodermal tumors: a retrospective analysis of 42 patients. Cancer 1988; 61:349-357.[Medline]
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Franken EA, Jr, Smith JA, Smith WL. Tumors of the chest wall in infants and children. Pediatr Radiol 1977; 6:13-18.[Medline]
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Faro SH, Mahboubi S, Ortega W. CT diagnosis of rib anomalies, tumors and infections in children. Clin Imaging 1993; 17:1-7.[Medline]
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Resnick D, Niwayama G. Diagnosis of bone and joint disorders 2nd ed. Philadelphia, Pa: Saunders, 1988; 4050-4052.
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HISTORY
FINDINGS
