Acromegaly without Imaging Evidence of Pituitary Adenoma

Abstract

Context: GH-secreting pituitary adenomas are nearly always visible on conventional magnetic resonance (MR) imaging. However, management and outcome of acromegalic patients lacking imaging evidence of GH-secreting pituitary adenomas are undefined. Objective: The aim was to evaluate surgical exploration for MR-invisible GH-secreting pituitary adenomas. Design and Setting: We conducted a retrospective review at two tertiary care centers. Patients or Other Participants: Consecutive acromegalic patients without imaging evidence of a pituitary adenoma on pre- and postcontrast, spin echo T1-weighted MR imaging and who lacked evidence of an ectopic (nonpituitary) source causing GH excess were included. Interventions: Surgical exploration with identification and resection of a pituitary adenoma was performed. Main Outcome Measures: Laboratory values (GH, IGF-I), surgical findings, and clinical outcome were analyzed. Results: Six patients (three males, three females; 3% of all patients) with suspected GH-secreting adenomas did not demonstrate imaging evidence of pituitary adenoma on conventional MR imaging. Three patients underwent a postcontrast, volumetric interpolated breath-hold examination MR-imaging sequence (1.2-mm slice thickness), which revealed a 4-mm pituitary adenoma not seen on the spin echo T1-weighted MR imaging in one patient. A pituitary adenoma was identified and removed in all patients (mean diameter, 5.6 mm; range, 5 to 6.7 mm). Histological analysis confirmed that the lesions were GH-secreting adenomas. All patients achieved biochemical remission after surgical resection. Conclusion: Acromegaly can be caused by GH-secreting pituitary adenomas that are not evident on conventional MR imaging. Adenomas in some of these patients become evident using volumetric interpolated breath-hold examination MR imaging. Surgical exploration of the pituitary gland in acromegalic patients with endocrine findings consistent with a GH-secreting adenoma but negative MR imaging can lead to identification and removal of an adenoma.