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

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.