Perinephric Mass in an Adult

Specimen Type:

Kidney

History:

A 67-year-old man presented with right perinephric mass and underwent radical nephrectomy.

Pathologic Features:

Grossly, a poorly circumscribed spongy sieve-like multicystic mass measuring up to 5.0 cm seen close to the inferior pole of the kidney. The individual cysts are smooth walled and contain yellow straw colored fluid. The mass is located wholly within the periphric fat and is adherent firmly to the renal capsule. The mass extends focally to outer surgical resection margins of perinephric fat.

Sections of the mass show a cystic lesion within the perinephric fat (Fig 1, 2) without involving the underlying renal parenchyma (Fig 3). Although the lesion predominantly consists of cysts of variable size (Fig 4), small tubules infiltrating the fibrous stroma are also seen (Fig 5). The cysts are separated by fibrous septa of variable thickness where prominent focal edema is present (Fig 6). The cysts are lined by flattened, cuboidal (Fig 7), tall columnar (Fig 8), or hobnail-like epithelium (Fig 9). The lining cells exhibit cytologic features ranging from bland-looking with small nuclei to markedly atypical with prominently enlarged nuclei and nucleoli (Fig 10, 11, 12).

Differential Diagnosis:

Multilocular cystic nephroma: Multicystic nephroma is an uncommon but distinctive lesion that presents as a mass clinically. Grossly, the lesion is usually solitary, unilateral and sharply delineated from the uninvolved renal parenchyma. The cut surface shows a multilocular appearance, and the wall of these cysts is thin and sometimes translucent and lacks papillary projections. Microscopically, it exhibits both an epithelial and a stromal component. The cysts are lined by a single layer of epithelial cells, which vary from flattened to low cuboidal or even columnar. Stratified zones may be present. Occasional cells exhibit atypical cytologic features including nuclear enlargement and hypechromasia. The stromal septa between the cysts consist of dense fibrous connective tissue with scattered loose fascicles of smooth muscle. Areas of blastema or nephroblastoma almost never occur in adult cystic nephromas. The prognosis after complete excision is excellent.

Renal simple cysts: This is the most common cystic abnormality encountered in the kidneys. Their occurrence increases with age. They are usually asymptomatic and are often detected at autopsy or an incidental finding in the radiological evaluation for other diseases. Grossly, there is no mass lesion appreciated, and cysts are scattered in the renal cortex, which can be solitary or multiple and bilateral. Microscopically, the cysts are lined by a single layer of cuboidal or flattened epithelium without cytologic atypia.

Diagnosis:

Grade 3 (Of 4) tubulocystic carcinoma.

Key Features:

  • Grossly, a well-circumscribe mass with spongy sieve-like multicystic appearance; no solid areas seen.
  • Microscopically
    • Tubules and cystic structures of marked variable size that are separated by delicate septa or by fibrous stroma of variable thickness.
    • A single layer of low-cuboidal to columnar lining epithelial cells with modest to abundant amounts of eosinophilic cytoplasm, often with areas of hobnail appearance.
    • Nuclei are round, with evenly dispersed chromatin, and readily evident nucleoli in some areas. Mitotic figures are rare.
  • Immunohistochemically, positive for CD10, Racemase, CK19 and 34BE12.
  • Ultrastructurally, abundant microvilli with brush border organization.

Comment: Tubulocystic carcinoma was initially described as “low-grade collecting duct carcinoma” in 1997, and it was emphasized that although the neoplasm had some features suggestive of collecting duct origin, it was distinctly different from classic CDC in many ways. In contrast to classic CDC, the tumors are well-circumscribed without hemorrhage and necrosis, and entirely composed of tubular and cystic structures of low nuclear grade, without desmoplastic stroma. A collaborative study of 33 patients shows that its biologic behavior is indolent and the metastastatic potential is less than 10%. This distinctive entity is rare and its histogenesis remains uncertain (proximal tubule or collecting duct). The tumor in this case is unique in that it is located wholly within the perinephric fat without renal parenchymal involvement.

References:

  1. MacLennan GT, Bostwick DG. Tubulocystic carcinoma, mucinous tubular and spindle cell carcinoma, and other recently described rare renal tumors. Clin Lab Med. 2005 Jun; 25(2):393-416.
  2. MacLennan GT, Farrow GM, Bostwick DG. Low-grade collecting duct carcinoma of the kidney: report of 13 cases of low-grade mucinous tubulocystic renal carcinoma of possible collecting duct origin. Urology. 1997 Nov;50(5):679-84.