Histological analysis of the kidney tumor-parenchyma interface

During enucleative partial nephrectomy excision is performed adjacent to the tumor edge. To better determine the oncologic propriety of enucleative partial nephrectomy we histologically examined the tumor-parenchyma interface.

Archived hematoxylin and eosin stained slides of 124 nephrectomy specimens were rereviewed. We evaluated representative sections of tumor abutting the renal parenchyma and overlying pseudocapsule/perirenal fat were selected at 4 mm(2) sectors apportioned 1, 2, 3 and 4 mm, respectively, from the tumor edge.

Median tumor size was 3.5 cm. Of the tumors 111 were malignant (90%) and 119 (96%) had a pseudocapsule with a median thickness of 0.6 mm. Of malignant and benign tumors 82% and 31%, respectively, had an intrarenal pseudocapsule (p < 0.001). Pseudocapsule invasion was noted in 45% of cancers and 15% of benign tumors (p < 0.04). Of pT1a cancers 36% showed intrarenal pseudocapsule invasion. No patient had positive surgical margins. Intrarenal pseudocapsule invasion correlated with clear cell renal cell carcinoma histology but not with cancer size, grade, necrosis or margin width. Inflammation, nephrosclerosis, glomerulosclerosis and arteriosclerosis decreased with increasing distance from the tumor edge. At 1 mm changes were moderate to severe in 38%, 32%, 20% and 17% of tumors while at 5 mm changes were mild in 2.5%, 0.8%, 0.8% and 4%, respectively (p <0.001). Mean arteriolar diameter decreased with tumor proximity (p < 0.0001).

Most renal cancers have an intrarenal pseudocapsule. Partial nephrectomy excision adjacent to the tumor edge appears to be histologically safe. Because 18% of cancers lacked a discernible intrarenal pseudocapsule and 25% of pT1a cancers showed intrarenal pseudocapsule invasion, extreme care is needed to avoid positive margins during enucleative partial nephrectomy.