(Answer)

Answer:

4. all of the above

The images show a multiloculated cystic mass of the superior pole of the right kidney. Such masses are being detected more often due to the improved sensitivity of US examinations and CT scans, as well as their increased frequency of use. The differential diagnosis in this patient includes neoplasm and renal cystic disease.[1] Echinococcus, segmental xanthogranulomatous pyelonephritis, abscess, and malakoplakia are not serious considerations, given the absence of a suggestive history or signs of infection. With no history of trauma, an organizing hematoma is unlikely. With no clinical signs of bruit, pulsatile mass, or hypertension, an arteriovenous fistula is also discounted.

Neoplasm

The differential diagnosis for neoplastic disease in this age group includes renal cell carcinoma and multilocular cystic nephroma. Approximately 5% of renal cell carcinomas present as multiloculated, fluid-filled masses. Typical findings include extensive calcification, blood, or hemorrhage within the cysts; thick, irregular enhancing walls and septa (Fig 2); and evidence of extension into the renal vein or of metastatic spread to regional lymph nodes or liver. The clinical features are nonspecific and are similar to those found in solid renal carcinomas. Half of the cases of von Hippel-Lindau disease have one or more renal cancers that are often multiloculated cystic masses.

Multiloculated cystic nephroma is a rare, nonhereditary cystic neoplasm with a capsule and septa that separate multiple epithelium-lined noncommunicating cysts. Its bimodal distribution peaks in children who are younger than four years of age and in adults (predominantly women) who are 30 to 70 years of age. Herniation of the tumor into the renal pelvis is suggestive of this entity, and hemorrhage is atypical.

The appearance of the CT scan and US examination for this patient may indicate Wilms' tumor, mesoblastic nephroma, and clear-cell sarcoma of the kidney. However, these are diseases of infancy or early childhood.

Benign Cystic Disease

Localized cystic disease of the kidney presents as multiple cysts involving only one portion of the kidney. It is neither genetically transmitted nor progressive, and it is not associated with neoplasia. The most suggestive finding on CT scan for localized cystic disease is the presence of a multiloculated mass that is not clearly demarcated from normal tissue. This appearance is due to the absence of a capsule. Smaller cysts may be present in the adjacent parenchyma that are slightly removed from the main mass.

Septated cysts are produced by two or more adjacent cysts or by a cyst with internal septations. Septations can be the result of hemorrhage or infection in a simple cyst, and they are often partial. The septations are either connective tissue or, in the case of adjacent cysts, compressed parenchymal tissue. Cystic spaces are characteristically large, and the septa are delicate.

Segmental multicystic kidney is often associated with other congenital renal anomalies. Although its appearance can be similar to that seen in this patient, it is usually diagnosed as a palpable mass in newborns.

Radiologic Criteria for Biopsy

Bosniak[2] has categorized cystic masses into four groups that reflect an increasing likelihood of malignancy. Category I is comprised of simple benign cysts that are well marginated with thin, smooth walls on CT scan. These do not enhance with contrast administration, and they measure less than 20 Hounsfield units (HU). On sonography, they are similarly well marginated, are anechoic, and have increased through transmission. Category II includes mildly complicated cysts, predominantly those with thin septa or small foci of wall or septal calcification. This category also includes simple cysts with attenuation measurements between 50 and 90 HU on CT scans, thought to be due to blood breakdown products within the cyst fluid. As with Category I cysts, contrast enhancement is absent. Category III includes indeterminate lesions that may have irregular margins, thickened or enhancing septa, and thick or irregular calcification. Category IV identifies probable malignancies that are likely to have thickened irregular or enhancing areas and calcification.

Category I lesions require no further follow-up. Category II lesions should be followed every three months for at least one year to ensure that no growth is occurring. Category III lesions require some type of histologic diagnosis, and Category IV lesions require surgical diagnosis.[3,4]

This case was identified as Category III due to uncertainty of margination and possible septal thickening. However, since a follow-up period of seven months showed no perceptible progression, the patient was classified as low risk in Category III, and a biopsy was performed percutaneously. Pathology established this mass to be benign.

References

1. Hartman DS, Davis CJ, Sanders RC, et al. The multiloculated renal mass: considerations and differential features. Radiographics. 1987;7:29-52.

2. Bosniak MA. The small (<=3.0 cm) renal parenchymal tumor: detection, diagnosis, and controversies. Radiology. 1991;179:307-317.