# Impact of Venous Drainage on Tumor Lateralization in Inferior Petrosal Sinus Sampling: Reappraisal With Literature Review

## TL;DR

This study examines how venous drainage affects the accuracy of inferior petrosal sinus sampling in locating corticotroph tumors for Cushing's disease.

## Contribution

The study reappraises the impact of venous drainage on tumor lateralization accuracy in IPSS and provides insights for surgical decision-making.

## Key findings

- IPSS lateralization agreed with the actual tumor side in 88% of histologically confirmed cases.
- False lateralization occurred in 12% of cases with dominant contralateral venous drainage.
- Prolactin-adjusted values did not alter the interpretation of false lateralization.

## Abstract

Introduction

Venous drainage patterns may compromise the ability of inferior petrosal sinus sampling (IPSS) to correctly lateralize corticotroph tumors in Cushing’s disease. We aimed to reappraise this effect in patients proceeding to transsphenoidal surgery (TSS) and to contextualize our findings with a brief review of the literature.

Methods

We retrospectively reviewed the records of 37 consecutive patients who underwent IPSS at our institution between April 2018 and March 2025. Of these, 28 subsequently underwent TSS based on IPSS findings and other clinical data. Corticotroph pituitary neuroendocrine tumors were histologically confirmed in 25 patients. We compared IPSS-indicated lateralization with the intraoperatively determined and histopathologically confirmed tumor side, and we systematically evaluated the influence of venous drainage patterns on false lateralization.

Results

Of the 25 histologically confirmed cases, IPSS lateralization agreed with the actual tumor side in 22 patients (88%), including eight with venous drainage from the tumor side toward the contralateral side. In contrast, three patients (12%) showed false lateralization, in which IPSS indicated the opposite side of the actual tumor. All three false-lateralized cases exhibited dominant contralateral venous drainage, and prolactin-adjusted values did not alter the interpretation. Overall, among 11 patients with dominant contralateral drainage, IPSS misidentified the tumor side in three (27%).

Discussion

IPSS demonstrated high lateralization accuracy in our cohort; however, dominant venous drainage from the tumor to the contralateral side may result in false lateralization. Careful assessment of venous outflow patterns is essential, particularly when IPSS findings contradict MRI-based lateralization, to support appropriate surgical decision-making.