Volume 30, Issue 175, September 2026

Unmasking a Contralateral Pituitary Neuroendocrine Tumor After Resection of a Decoy Lesion: A Case Report

Justyna Kowalczewska^♦

Department of Neurosurgery, University Clinical Hospital in Poznan, Poznan University of Medical Sciences, Poznan, Poland

^♦Corresponding author
Justyna Kowalczewska, Department of Neurosurgery, University Clinical Hospital in Poznan, Poznan University of Medical Sciences, Poznan, Poland

ABSTRACT

Multiple pituitary adenomas (MPA) are a rare condition characterized by the presence of 2 or more histologically and/or radiologically distinct pituitary tumors in a single patient. Their diagnosis may be challenging, particularly when one lesion obscures another on preoperative imaging. It can potentially result in persistent hormonal hypersecretion after surgery. This case report presents a 57-year-old man with acromegaly who underwent transsphenoidal resection of a right-sided pituitary macroadenoma. Preoperative MRI demonstrated a lesion in the right and central part of the pituitary gland. Despite surgery, biochemical remission was not achieved - with persistently elevated IGF-1 levels. Histopathological examination did not demonstrate a GH-secreting adenoma. Follow-up MRI performed six months after surgery revealed a hypointense lesion in the left part of the pituitary gland located near the cavernous sinus, which had not been visible on the preoperative MRI. Due to persistent biochemical activity and the newly identified contralateral lesion, a second transsphenoidal surgery was performed. Histopathological examination confirmed a GH-positive pituitary neuroendocrine tumor. Three months after the second surgery IGF-1 levels had normalized, indicating biochemical remission. Follow-up MRI showed no residual or recurrent tumor. MPA represents a diagnostic and therapeutic challenge that requires a multidisciplinary approach involving: endocrinologists, radiologists and neurosurgeons to ensure accurate diagnosis and effective treatment. Persistent hormonal hypersecretion despite gross total resection should raise suspicion of an additional adenoma - particularly when the initial lesion is nonfunctioning. Careful preoperative and postoperative radiological assessment, together with endocrinological follow-up, is essential for identifying responsibility lesions and achieving biochemical remission.

Keywords: decoy lesion; multiple pituitary tumors; responsibility lesion; acromegaly; growth hormone–secreting pituitary adenoma; transsphenoidal surgery

Medical Science, 2026, 30, e191ms3982

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DOI: https://doi.org/10.54905/disssi.v30i175.e191ms3982

Published: 23 September 2026