# Pituitary Neuroendocrine Tumors Extending Primarily Below the Sella and into the Clivus: A Distinct Growth Pattern with Specific Challenges

## TL;DR

This study examines rare pituitary tumors that grow below the sella into the clivus and sphenoid sinus, highlighting their unique challenges in diagnosis and surgery.

## Contribution

The paper identifies a distinct growth pattern of pituitary neuroendocrine tumors and emphasizes the need for tailored surgical approaches.

## Key findings

- Tumors extending into the clivus and sphenoid sinus are associated with high rates of cavernous and sphenoid sinus infiltration.
- Complete surgical resection was achieved in only 31% of cases, with residual tumors often found in the cavernous sinus or clivus.
- Preoperative pituitary dysfunction was common, and surgical approaches must be adapted to address clival infiltration.

## Abstract

Pituitary neuroendocrine tumors extending primarily below the sella into the clivus and sphenoid sinus are rare. Their specific challenges have largely been neglected in the literature. As one body of cavernous cancellous bone, the clivus offers a locus minoris resistentiae for diffuse tumor spread away from the classically addressed suprasellar region and optic chiasm. This study defines growth of these tumors in terms of three clival anatomical regions with different surgical accessibility and reports a high rate of preoperative pituitary dysfunction and infiltration of the cavernous sinus as well as the sphenoid sinus, posing a challenge to complete surgical resection with unexpected tumor residuals. Mechanisms of this growth pattern are discussed and help to plan surgical resection of these tumors.

Evaluation of pituitary neuroendocrine tumors remains complex depending on the exact growth pattern, involvement of critical neurovascular structures, pituitary function and endocrinological activity of the tumor. A predominant growth into the sphenoid sinus and clivus poses specific challenges. We reviewed 557 surgeries for pituitary neuroendocrine tumors in an endonasal endoscopic technique performed between 1 January 2015 and 31 August 2025 to identify 13 cases (2.3%). Clinical, radiological and surgical data were selected by chart review. Thirteen cases aged from 31 to 68 years with almost exclusively non-functioning or clinically silent tumors (92%) were identified. Clival infiltration was restricted to the dorsum sellae in 2/13 (15%), spread to the floor of the sphenoid in 6/13 (46%) and extended inferior to the sphenoid in 5/13 (38%) cases with a high rate of cavernous sinus (62%) and sphenoid sinus infiltration (69%). Complete resection was achieved in 31%, and the residual tumor was clival/sphenoidal in 5/13 cases or within the cavernous sinus in 6/13 cases. The diaphragma sellae was reported to be intact in 92% of cases, and postoperative transient arginine vasopressin deficiency did not occur. Pituitary neuroendocrine tumors predominantly growing below the sella and infiltrating the clivus and sphenoid present specific challenges with a high rate of preoperative pituitary insufficiency, frequent cavernous sinus infiltration and postoperative tumor residuals in the cavernous sinus, sphenoid bone and clivus which are sometimes difficult to delineate. The surgical approach must be tailored specifically to treat the clival infiltration zone to reduce the risk of recurrence.