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Excerpt
I read with great interest the recent article entitled "Papillary (Chromophil) Renal Cell Carcinoma: Histomorphologic Characteristics and Evaluation of Conventional Pathologic Prognostic Parameters in 62 Cases" by Dr. M.B. Amin et al.,1 published in the June 1997 issue of the American Journal of Surgical pathology. The authors evaluated the histology of 62 papillary renal cell carcinomas (PRCC) and analyzed the correlation between conventional pathologic prognostic features and actual clinical outcome. They believed that PRCC represents a distinct subtype of renal cell carcinoma in terms of histologic features, cytogenetic findings, and prognostic implication. The identification of PRCC is important because of its better long-term survival rate, compared with the conventional renal cell carcinoma, irrespective of the stage of the disease. Microscopically, PRCC is relatively well circumscribed, characterized by predominantly papillary or tubulopapillary patterns and often associated with a thick fibrous capsule, foamy histiocytes, tumor necrosis, hemorrhage, and multifocality.
I agree with the authors that the morphologic definition of this tumor should be based on the overall architecture rather than by an arbitrary percentage of the papillary pattern. However, I think there is another characteristic light microscopic feature of PRCC that is worth mentioning. In a review of renal cell carcinomas in the pathology file of Queen Mary Hospital (which is one of the major regional hospitals in Hong Kong) from 1986 to 1997, 10 cases of PRCC were found. Nine came from nephrectomy specimens, and the remaining one was an autopsy case. Tumor size ranged from 1 cm to 16 cm in greatest dimension. All were fixed in 10% neutral buffered formalin before processing. The histologic features of these tumors in the hematoxylin and eosin sections were assessed. The Fuhrman's nuclear grades of the cases varied (grade I × 5, grade II × 4 and grade III × 1). Frequent longitudinal nuclear grooves were seen in all of the PRCC (Fig. 1), apart from the other features mentioned in Dr. Amin's article. The nuclear grooves were especially obvious in the low-grade tumors. The identification of nuclear grooves in PRCC had also been briefly described in the previous reports.2,4,5 Papillary renal cell carcinoma is considered as one of the major differential diagnosis in the fine needle aspiration cytology of extrathyroid lesions associated with prominent longitudinal nuclear grooves.3 Ultrastructural examination had been performed in some of our cases and confirmed their proximal tubule differentiation, as suggested by the prominent luminal brush borders and frequent basal plasma membrane infoldings. Glycogen granules were relatively scant compared with the conventional renal cell carcinoma. Moreover, deep, longitudinal nuclear grooves were commonly identified in many of the oval-shaped tumor cell nuclei (Fig. 2). These nuclear grooves resembled those seen in papillary thyroid carcinoma. Pseudonuclear cytoplasmic inclusions, however, were not features in PRCC, both under light and electron microscopy.
Because the prognosis of PRCC is distinctly different from the other variants of renal cell carcinoma, correct diagnosis based on detailed histologic assessment is important, especially in centers where there is no cytogenetic service. The recognition of nuclear grooves in PRCC may represent another "eye-catching" cytologic, as well as histologic, feature that helps to distinguish PRCC from its mimickers, including collecting duct carcinoma. This is especially true in cases of PRCC in which the tubulopapillary pattern is markedly distorted by the associated inflammation and stromal desmoplasia.
