Gross Features: Collecting duct carcinomas (synonym: carcinoma of the ducts of
Bellini) are usually large tumors located in the medulla or central parts of the
kidney with extension into the perinephric fat and invasion of the renal pelvis. The
white colored and firm cut surface is interspersed with foci of necrosis and the
tumor often has an indistinct border with the surrounding kidney because it is
infiltrative. Intra-renal satellite nodules and parenchymal infarction are common as
a result of severe angioinvasiveness. Regional spread with infiltration of the
ipsilateral adrenal and lymph node metastases are common.
Microscopic Features: Light microscopically, the basic cell type of collecting duct
carcinoma is medium sized tumor cells with a basophilic, sometimes light cytoplasm
due to a pronounced formation of endoplasmic reticulum and varying degrees of
glycogen deposits often forming typical hobnail cells. Electron microscopically, the
lateral and basal cell membranes are orientated linearly without interdigitations and
invaginations resembling those of the principal cells of the medullary collecting
duct. An eosinophilic (granular) cell variant as well as a spindle
cell/polymorphic/sarcomatoid cell type with anaplastic nuclei is common. As a rule,
the growth pattern is tubular combined with a microcystic, short papillary,
pseudopapillary and solid pattern associated with an intensive desmoplastic stromal
reaction as well as granulocytic infiltration.
Differential diagnosis: Chromophil RCC, urothelial carcinoma
