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In a patient with a temporal swelling, imaging is advisable before any surgical intervention.
A girl of 4 was referred because of a right temporal swelling present for five months. This had expanded rapidly and hugely after biopsy by a general surgeon. The specimen was reported as temporal aneurysmal bone cyst. On examination, a soft cystic lesion occupied the squamous part of the right temporal bone. The ear canal was entirely normal. A high definition CT scan showed the multiple fluid levels classically seen in such lesions (Figure 1). The mass was fully excised by a combined neurosurgical and otological procedure. Cyst tissue was found in the posterior mastoid segment but there was no involvement of cranial nerves or the inner ear. A year after surgery CT scanning shows no evidence of recurrence.
Aneurysmal bone cyst is the term used by Jaffe and Lichtenstein in 1942 to describe benign bony lesions seen mainly in vertebrae and long bones and occurring usually in the first and second decades of life1. Aneurysmal bone cysts of the skull are rare2 representing only 2-6% of cases, more than half of which involve the orbit and the occiput. Those arising from the temporoparietal region and the basal sinuses show a tendency to intracranial expansion1,3.
Aneurysmal bone cysts usually present as an enlarging well circumscribed mass (often tender to palpation1) and come to medical attention early in life (mean age 14.5 years)1. The manifestations can include headaches, neurological deficits, cranial nerve palsies, raised intracranial pressure, seizures and rarely intracerebral haemorrhage1. The cyst can erode bone; destruction of the posterior ear canal and Fallopian canal with subsequent facial nerve exposure has been reported4. Important aspects to consider before intervention are, first, that in about half of the cases the lesion is associated with an intracranial mass effect, due either to expansion of the inner table of the skull or to epidural extension of the lesion1; and, secondly, that temporoparietal and basal sinus aneurysmal bone cysts have a high tendency (75%) to expand intracranially1,3. Usually the lesion remains within the pericranial or dural covering; however, there are reports of intradural aneurysmal bone cyst5 and also of spontaneous intracerebral haemorrhage1 and intraparenchymal haematoma.
Radiological investigation with CT2 or MRI6 is usually diagnostic. The treatment of choice is surgical excision. In the cranium and spine complete excision is often impossible because of difficult access, in which case preoperative embolization or postoperative cryotherapy or radiotherapy should be considered.
We conclude, patients with a temporal mass should be referred to specialists familiar with management of aneurysmal bone cysts. CT scan and MRI are the appropriate investigations to reveal the extent of the mass, any intracranial, middle or inner ear involvement and vascular complications. In the present case the temporal mass expanded rapidly after biopsy because of haemorrhage. This is typical. Occasionally these cases are further complicated by intracranial involvement. Clinicians should be sensitive to the implications of masses presenting behind the ear, particularly in children and young adults.