(RadioGraphics. 1985;5:175-192.)
© RSNA, 1985

The clandestine renal cell carcinoma: Atypical appearances and presentations

¹ From the Department of Radiology, Durham Veterans Administration Hospital, Durham, North Carolina.
² From the Department of Radiology, Duke University Medical Center, Durham, North Carolina.

The radiologic diagnosis of renal cell carcinoma continues to be challenging. The small subgroup of atypical tumors described here exemplifies this challenge. Important summarizing points are as follows:

1. High dose excretory urography with nephrotomography is the screening procedure of choice for renal cell carcinoma. A small percentage of tumors will escape detection by this method, however. When the clinical suspicion of a malignant neoplasm of the kidney is high and the urogram is negative, more sensitive screening with computed tomography is indicated.

2. Renal cell carcinoma does occur rarely in the pediatric population, having a peak incidence at 9 years of age. The gross morphology and resultant appearance of this neoplasm in imaging studies are unfortunately indistinguishable from those of Wilms' tumor. Factors that favor the diagnosis of renal cell carcinoma are older age at presentation, hematuria, renal calcification without obvious mass, and bone metastases.

3. Spontaneous renal or perirenal hemorrhage is most frequently the result of over-anticoagulation, but on occasion may be secondary to an underlying structural abnormality of the kidney such as renal cell carcinoma. Computed tomography can usually demonstrate the associated tumor mass except when it is small (less than 2 cm). Dynamic scanning is particularly useful in documenting contrast enhancement which occurs in solid tumors but does not occur in an intrarenal hematoma.

4. Hemorrhagic renal cell carcinoma may have a computed tomographic appearance similar to benign "hyperdense" cyst. Although not always present, certain findings are suggestive of tumor rather than cyst; namely, poor marginal definition, central inhomogeneity, and contrast enhancement. In difficult cases, ultrasonography may be helpful in excluding a high attenuation tumor if classic cyst criteria are demonstrable.

5. Some renal masses seen on computed tomograms are not classic solid tumors, and yet they fail to satisfy all of the criteria for a simple cyst. Such "cyst-like" masses are characterized by an elevated attenuation coefficient, peripheral calcification, irregular contour, or thick peripheral rim. Their nature (cyst versus tumor) is indeterminate by CT criteria. In such indeterminate lesions, active infection or associated tumor should be excluded by cyst puncture as causes of cyst atypia.

6. Renal cell carcinoma may occasionally be found within renal cysts. Macroscopic tumor has a characteristic location on the cyst wall closest to the renal hilum. Knowledge of this virtually constant relationship facilitates recognition of this unusual entity both on ultrasound and computed tomography.

The purpose of this review has been to emphasize that an occasional renal cell carcinoma will present atypically or display unusual imaging appearances or both. It is our hope that this discussion will heighten awareness of the spectrum of findings that one may encounter, and that this will lead to earlier radiologic diagnosis.

It has not been our purpose to attempt to illustrate all of the unusual manifestations of renal cell carcinoma. The interested reader is referred to the literature for discussions regarding bilaterality (18) and central necrosis (15) as well as malignancy in association with chronic hemodialysis (17), multilocular cysts (6), tuberous sclerosis (8), and von Hippel Lindau disease (12).