Pituitary Adenomas with Subarachnoid Invasion: Surgical Nuances and Outcomes

Introduction: A small subset of pituitary adenomas invade the suprasellar subarachnoid space and involve critical neurovascular structures. Compared to typical adenomas which respect the arachnoid plane, resection of these tumors present additional challenges. A unique operative approach including an expanded bony exposure, careful extracapsular dissection of the tumor from surrounding neurovascular structures, and meticulous multi-layered reconstruction is required to achieve maximal safe resection, avoid iatrogenic injury, and prevent post-operative complications. This study aims to describe the presentation, nuances in surgical management, and outcomes of pituitary adenomas with subarachnoid invasion.

Methods: Data from 321 patients who underwent an endoscopic endonasal approach (EEA) for pituitary adenoma resection was prospectively collected from 2018 to 2023 and analyzed as a retrospective cohort. Thirteen patients harboring pituitary adenomas with subarachnoid invasion were identified. These tumors underwent a modified surgical approach involving microdissection from surrounding neurovascular structures to accomplish maximal safe resection. Patient demographics, tumor characteristics, and outcomes were compared across patients with and without subarachnoid invasion.

Results: Approximately 4% of patients (13/321) undergoing EEA for pituitary adenoma resection were found to have subarachnoid invasion as determined by intra-operative observation. There was no difference in age (p = 0.67) or gender (p = 0.67) across patients with and without subarachnoid invasion. Moreover, there was no difference in tumor pathology (p > 0.05), tumor functional status (p = 0.16), tumor size (p = 0.43), apoplexy (p = 0.88), presence of cavernous sinus invasion (p = 0.62), or history of prior surgery (p = 0.24). Compared to patients without subarachnoid invasion, those with subarachnoid invasion were more likely to have subtotal tumor resection (53% vs. 11%, p < 0.00001) and require additional treatment (33% versus 13%, p < 0.01) including medical therapy, radiation, or repeat resection. While rates of transcavernous surgery remained similar between the two groups (53% vs. 51%, p = 0.88), patients with subarachnoid invasion were more predominantly Knosp grade 4 (27% vs. 4%, p < 0.0001) and were more likely to have residual within the cavernous sinus (27% vs. 5%, p < 0.001). Although patients with subarachnoid invasion experienced greater intra-operative CSF leak rates than patients without invasion (100% vs. 35%, p < 0.00001), the rates of postoperative CSF leak (0% vs. 3%, p = 0.51) were similar across groups. Additional postoperative interventions were comparable regarding medical therapy (13% vs. 5%, p = 0.14) and stereotactic radiosurgery (7% vs. 2%, p = 0.21), although patients with subarachnoid invasion experienced higher rates of repeat resection (13% vs. 1%, p < 0.001) and proton beam radiation therapy (13% vs. 0%, p < 0.0001). Patients with subarachnoid invasion also exhibited a higher incidence of diabetes insipidus (27% vs. 4%, p < 0.001) and postoperative hematomas (7% vs. 0.6%, p = 0.02).

Conclusion: Pituitary adenomas with subarachnoid extension represent a distinct surgical challenge, requiring microsurgical dissection, detachment, devascularization, and debulking techniques more comparable to the resection of a meningioma or craniopharyngioma than a typical pituitary adenoma, to avoid injury to adjacent neurovascular structures. Yet, even with this recognition and approach, pituitary adenomas with subarachnoid invasion remain challenging tumors with increased rates of subtotal resection, intra-operative CSF leak, postoperative diabetes insipidus, post-operative hematomas, and need for adjuvant interventions.

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No conflict of interest has been declared by the author(s).

Publication History

Article published online:
05 February 2024