Microscopic Tubulovenous Communications in Nonneoplastic Kidneys: A Single-Center Case Series and Review of the Literature

Abstract

Rationale & Objective

Pathological connection between the kidney tubules and veins is known as a microscopic tubulovenous communication we refer to as a tubulovenous fistula (TVF). This finding has been reported in a few small case reports, but no systematic examination of cases across various clinical settings detailing their histologic spectrum and associated clinical/pathologic findings has been performed.

Study Design

Case series and literature review.

Setting & Participants

Nonneoplastic kidney pathology reports from an academic medical center (February 1, 1990, to February 1, 2024) were queried for mention of TVF. In total, 30,537 nonneoplastic kidney reports were queried, and 22 cases of TVF were identified.

Results

In total, 72.7% of TVF cases were from native kidney biopsies. Median patient age was 66 (range, 25-84) with a male predominance (68.2%). Clinically, 82.4% had microscopic hematuria, and 17.6% had gross hematuria. TVFs were usually singular and involved arcuate size veins. Microscopically, 95.5% of cases had acute tubular injury, and 73.3% had at least focal pathologic intratubular casts/calcium crystals. In total, 56.3% of native cases had interstitial nephritis. Of the transplant cases (n = 6), 66.7% exhibited rejection.

Limitations

Laboratory data, clinical follow-up, and original slides were not available in all cases examined. Although rare in our repository, TVFs are likely an under-reported finding. In addition, the focality of TVFs could play a role in their limited rate of detection.

Conclusions

This is the largest case series exploring the clinical and histologic features associated with TVFs in the kidney. Our findings support the assertion that TVFs are associated with hematuria without glomerulonephritis and occur in the setting of significant tubular injury, intratubular casts/crystals, and obstructive phenomena likely because of disruption of tubular basement membranes adjacent to veins.

Plain Language Summary

Our study explores a rare feature found in medical kidney biopsies called tubulovenous communications, in which small blood vessels connect with kidney tubules. These communications can sometimes be overlooked or not recognized because of their rarity. We reviewed a series of biopsies to identify and describe these communications and their associated findings in the kidney. By looking at these biopsies, we learned that these communications are more common when there is background kidney inflammation. Our findings highlight the importance of recognizing tubulovenous communications, which could potentially explain blood in the urine in patients with kidney inflammation but no damage to the glomerulus. Our findings also suggest that inflammation may be a mechanistic explanation for the formation of these connections.