Peritumoral cysts associated with pituitary macroadenoma

OBJECT Peritumoral cysts are benign nonneoplastic cysts that are found adjacent to extraaxial brain tumors such as meningiomas, schwannomas, craniopharyngiomas, and esthesioneuroblastomas. Peritumoral cysts associated with pituitary macroadenomas have not been previously described in the literature. The authors report 6 cases of giant macroadenoma-associated peritumoral cysts and delineate their imaging spectrum. METHODS The authors retrospectively reviewed the records of 179 patients diagnosed with pituitary macroadenomas who underwent tumor resection at their institution and had preoperative MRI scans available for review. The patients were evaluated for the presence of associated peritumoral cysts. Clinical presentation, histopathology, follow-up time, tumor and peritumoral cyst dimensions were recorded. Signal intensity on T1-weighted, T2-weighted, diffusion-weighted, and FLAIR sequences, as well as pre- and postcontrast appearance, were determined. RESULTS Six patients (3.4%) with associated peritumoral cysts were identified in our cohort of 179 patients with pituitary macroadenoma. Twelve patients in the cohort had giant macroadenomas (≥ 4.0 cm), and 50% of these tumors had associated peritumoral cysts with significant extrasellar extension of the macroadenoma. Only tumors with craniocaudal, transverse, and anteroposterior diameters of 3.6 × 3.4 × 4.2 cm to 7.0 × 7.4 × 6.8 cm (mean 5.3 × 5.1 × 5.6 cm), respectively, had associated peritumoral cysts. The growth pattern in all tumors was suprasellar, with predominant anterior and lateral extension. Cysts showed T1-weighted, T2-weighted, and FLAIR hyperintensity in 67%, 67%, and 60% of patients, respectively. There was no contrast enhancement of the cyst wall or fluid contents in any patient. Postoperatively, cysts had completely resolved (4 of 5) or significantly decreased in size (1 of 5). One patient was lost to follow-up. CONCLUSIONS Macroadenoma-associated peritumoral cysts are rare, benign, and likely nonneoplastic fluid collections that do not represent neoplasm. These cysts display a predictable pattern of hyperintensity on T1-weighted, T2-weighted, and FLAIR sequences and do not enhance. They most likely represent proteinaceous CSF in a sulcus or cistern that becomes trapped (encysted) by anterolateral extension of unusually large macroadenomas. Peritumoral cysts may facilitate resection of the associated macroadenoma by providing a cleavage plane.