Large suprasellar aneurysms imitating pituitary tumour

SUMMARY Two patients had large (20-30 mm) suprasellar aneurysms with clinical findings resembling an expanding pituitary tumour. One aneurysm was giant (30 mm). Its delayed diagnosis for six years led to severe chiasmal compression. The other aneurysm was compressing the optic nerve. Visual improvement resulted after surgery. This report records two cases of large, unruptured suprasellar aneurysms presenting with unilateral visual field loss and a slowly progressive course compatible with a pituitary tumour. They are pre-sented to call attention to this situation which, if unrecognised, can lead to delayed diagnosis and serious errors in management. An early recorded case of a large carotid aneurysm simulating a pituitary tumour was re-ported by Mitchell (1889). Postmortem examina-tion revealed an aneurysm 22 mm (one inch) in diameter embedded in the sella turcica. This aneurysm had "lifted the chiasm until this parted in the middle line, leaving a nerve on each side.... " Cushing (1912) reported a case with pro-gressive failure of vision and optic atrophy from an hypophyseal adenoma with an interpeduncular aneurysm. He noted that the aneurysm may play the same role as the interpeduncular tumour by its compression effects. Because both a large intracranial, unruptured aneurysm and an expanding tumour can produce pressure on adjacent structures, it has been sug-gested that they cannot be distinguished by visual fields (Walsh, 1964). However, in another report (Bird et al., 1970) the pattern of the visual field loss and temporal profile in unruptured supra-sellar aneurysms appeared to differ from that of intrasellar or parasellar tumours