A true aneurysm of the superficial temporal artery: Is there an underlying pre-disposition to such rarities?

INTRODUCTION: A 32 year old man presented to our vascular clinic with a lump over the left eyebrow. It had become larger in size and was cosmetically unacceptable. PRESENTATION OF CASE: Clinical examination of the lump demonstrated a pulsatile swelling consistent with an aneurysm of the superficial temporal artery (STA). Doppler ultrasound demonstrated arterial flow within the lump that could be controlled with pressure over the proximal branch of the vessel. The STA aneurysm was excised under local anaesthesia by ligation of the feeding and draining branches. It measured 3.4cm×3.7cm. Histological examination confirmed a rare finding of a true aneurysm of the STA. DISCUSSION: Aneurysms are classified into false or true types, with false aneurysms of the STA accounting for 95% of cases reported. It has therefore been suggested that true aneurysms of the STA may develop from a yet unknown pre-existing vessel condition. The histological findings in our case demonstrated myxoid/mucoid deposits replacing elastin fibres of the media layer, in addition to cystic lesions seen in the adventitia. These features were thought to be nonspecific but have been reported in rare conditions known as cystic adventitial disease and cystic medial necrosis. Such is their obscurity that we speculate that both of these may represent variations of the same underlying pathology. As myxoid/mucoid changes are also noted in more well-known connective tissue disorders including Marfan's syndrome, imaging was arranged to screen our patient for thoracic and abdominal aneurysms. These proved negative and there were no Marfanoid features noted prior.
CONCLUSION: Aneurysms of the STA are easily treated by surgical excision. This should be considered when they become large, painful or are cosmetically undesirable. Unusual histological findings in the specimen may indicate a connective tissue disorder that should be investigated if indicated.