Decoy Lesion in Functional Multiple Pituitary Adenomas: Literature Review and Illustrative Cases on Diagnostic Pitfalls and Surgical Strategies.

Abstract

Multiple pituitary adenomas (MPA), particularly those involving functioning adenoma, represent a special subtype of pituitary adenomas that pose dual challenges in diagnosis and treatment. In this setting, the coexistence of hormonally active and silent lesions may result in a diagnostic pitfall when a radiologically dominant tumor does not correspond to the hormonally responsible lesion. This misleading lesion, often referred to as decoy lesion, can adversely influence surgical decision-making in patients with MPA. We systematically reviewed English-language case reports of multiple pituitary adenomas published between 2000 and 2024 in PubMed, Web of Science, and Embase and present 2 illustrative cases. Lesions were classified as responsibility lesions or decoy lesions based on an operational definition incorporating endocrine outcomes, radiological features, and surgical findings. A total of 35 patients from 24 case reports met the inclusion criteria. The mean age was 40 years, with 12 male and 23 female patients. The most common clinical manifestations were acromegaly (n = 13, 37%) and Cushing's syndrome (n = 11, 31%). Our findings indicate that, compared with decoy lesions, responsibility lesions are less conspicuous on preoperative MRI and usually smaller in size. Overall, 43% of these patients (15/35) did not achieve biochemical remission after the initial surgery, with missed identification of the responsibility lesion reported in a substantial proportion of cases. Identifying decoy lesion and distinguishing it from responsibility lesion may improve surgical planning and endocrine outcomes in complex MPA cases.