Introduction: 'Silent' somatotropinomas are defined as GH-immunopositive pituitary adenomas without clinical symptoms of acromegaly and GH elevation in peripheral blood. Such tumours used to be considered as rare. However, recent data has indicated that they are more frequent than previously thought. The present paper shows that pituitary adenomas, diagnosed before surgery as nonfunctioning, often display GH immunopositivity.
Material and methods: Fifty six patients with pituitary adenomas were included in the study. All the patients underwent transphenoidal adenectomy. In 37 patients before the surgery, clinically nonfunctioning pituitary adenomas (CNFPAs) were diagnosed. In 19 patients, acromegaly was diagnosed. All the excised tumours were examined immunohistochemically using the primary antibodies against the pituitary hormones or their subunits.
Results: All the adenomas in the patients with acromegaly were immunopositive for GH. Among the pituitary tumours diagnosed before the surgery as clinically nonfunctioning, 45.9% showed GH immunopositivity. Both somatotropinomas with acromegaly and 'silent' GH-immunopositive adenomas most often co-expressed prolactin, whereas GH-immunonegative nonfunctioning adenomas expressed mainly LH and/or FSH. In three cases of 'silent' somatotropinomas, IGF-1 levels were slightly elevated, suggesting that these patients may present a 'low-symptomatic' acromegaly.
Conclusions: GH-immunopositivity occurs in nearly half of 'clinically' nonfunctioning pituitary adenomas. Because of that, IGF-1 determination in blood before the surgery, and immunohistochemical examination of adenoma for GH after the surgery, should be performed as standard in all patients suffering from pituitary tumours, irrespective of the presence or absence of acromegaly symptoms.