When Appearances Deceive: A Silent Somatotroph Macroadenoma Presenting With Acromegaloid Features and Paradoxically Low Insulin-Like Growth Factor-1

Silent somatotroph adenomas are uncommon pituitary neuroendocrine tumours (PitNETs) of the PIT1 lineage that express growth hormone (GH) immunohistochemically but without biochemical evidence of acromegaly. We report the case of a 32-year-old male patient referred with recurrent epistaxis, headache, right-sided diplopia, and third cranial nerve palsy. Clinical examination revealed acromegaloid features including frontal bossing, spade-like hands, and coarse facies, which were strongly suggestive of longstanding GH excess. However, preoperative insulin-like growth factor-1 (IGF-1) was paradoxically low at 13.1 nmol/L (reference range 15.5-33.1 nmol/L), creating a striking clinical-biochemical discordance. MRI demonstrated a giant sellar and suprasellar mass with chiasmal compression, right cavernous sinus invasion, and extension into the paranasal sinuses. The patient underwent endoscopic transsphenoidal resection. Neuropathology confirmed a densely granulated PIT1-lineage somatotroph adenoma with scattered GH positivity, diffuse Pit-1 staining, and a Ki-67 index below 2%. This case highlights the diagnostic challenge posed by silent somatotroph adenomas, underscores the limitations of biochemical assessment alone, and reinforces the essential role of histopathology and immunohistochemistry in establishing a definitive diagnosis. Long-term endocrine and neurosurgical surveillance is strongly recommended given the potential for phenotypic transformation to a functioning acromegaly syndrome.