Atypical pituitary adenomas: 10 years of experience in a reference centre in Portugal

Primary pituitary tumours are classified by the World Health Organization as typical adenoma, atypical adenoma, or carcinoma. Information on the incidence and prevalence of these pituitary tumours is limited, and these data in Portugal are scarce, obsolete, or non-existent. Our study evaluates pituitary adenomas (PA) in the population of Lisbon, and it aims to describe the prevalence of all subgroups in order to revise the incidence of the 'atypical' histological type and its correlation to tumour subtype, invasion, and recurrence.

A retrospective, descriptive analysis of patients with PA diagnosed between 2004 and 2013 was performed at Santa Maria University Hospital, a national reference centre.

Of the 220 PA cases diagnosed, 28 (12.7%) fulfilled criteria for atypical lesions, and within that group, 23 were macroadenomas (82.1%) and 13 showed radiological evidence of invasion (46.4%). Ages ranged from 29 and 81 years (mean, 53.4 years). Eleven patients (39.3%) had functional tumours. Sixteen of the 28 patients (57.1%) experienced tumour recurrences; in the 100 adenomas monitored for more than 5 years, the recurrence rate in atypical PA was 7 times higher than in typical PA. Immunohistochemically, 28.6% of the tumours stained positively for ACTH, 25% for gonadotrophins, and 17.9% for prolactin. The proliferation index (Ki67) ranged from 3% and 25% (mean, 6.4%).

Atypical PAs make up 12.7% of all surgically treated PA cases, and they tend to be invasive and recurrent macroadenomas. We found no differences in metastatic potential between typical and atypical PA.