Pituitary adenomas with subarachnoid invasion: clinical characteristics, radiographic features, surgical management, and outcomes.

OBJECTIVE: A subset of pituitary adenomas invade the subarachnoid space, encase critical neurovascular structures, and portend significant surgical morbidity. Resection of these lesions requires a modified surgical approach involving an expanded bony exposure and meticulous microsurgical dissection to avoid injury to the involved neurovascular structures. The goal of this study was to elucidate the clinical and radiographic features of subarachnoid adenomas and to characterize the outcomes after resection of these challenging tumors.

METHODS: Data were collected from 436 consecutive pituitary adenomas that underwent endoscopic endonasal approaches (EEAs), combined EEA/open transcranial approaches, and open transcranial approaches for tumor resection from 2018 to 2024. Clinical features, imaging characteristics, and clinical outcomes were compared across tumors with and without subarachnoid invasion.

RESULTS: Subarachnoid invasion was identified in 8% of pituitary adenomas that underwent resection. Compared to adenomas without subarachnoid invasion, subarachnoid adenomas demonstrated increased nodular invasion, subarachnoid vessel encasement, and tumor size on imaging. Prior surgical intervention and corticotroph/lactotroph histology were significant risk factors for subarachnoid invasion. EEA was the primary surgical approach utilized for resection (80%), although combined EEA/open transcranial (14%) and open transcranial approaches (6%) were also utilized for subarachnoid adenomas. Gross-total resection rates were lower for subarachnoid adenomas (49% vs 89%, p < 0.00001), and patients with subarachnoid adenomas were more likely to require additional interventions (40% vs 13%, p < 0.0001). Tumors with subarachnoid invasion were also associated with increased postoperative hematomas (p = 0.05), perforator infarcts (p < 0.01), and postoperative hydrocephalus requiring shunt placement (p < 0.001). In addition, subarachnoid adenomas were associated with increased rates of permanent vasopressin deficiency (p < 0.01) and adrenal insufficiency requiring permanent hormone replacement (p = 0.02). Based on multivariate analysis, the NETS score was developed to preoperatively predict subarachnoid invasion, incorporating nodular invasion (2 points), subarachnoid vessel encasement (2 points), maximum tumor diameter > 20 mm (1 point), and history of prior surgical intervention (1 point). NETS scores ≥ 3 demonstrated 91% sensitivity and 99% negative predictive value for subarachnoid invasion.

CONCLUSIONS: Subarachnoid adenomas are associated with high morbidity due to their close association with critical neurovascular structures. Invasive tumor biology and prior arachnoid disruption likely contribute to the nodular invasion and subarachnoid vessel encasement that are characteristic of these challenging tumors. The NETS score is a highly sensitive predictive score that can assist in preoperative identification and facilitate appropriate surgical planning.