Histiocytosis X of the petrous bone in the adult: MRI.

Two cases of histiocytosis X in young adults with involvement of only the petrous bone are reported. In the first symptoms and signs consisted of a seventh nerve palsy of gradual onset over 3 years, and in the second, of pulsatile tinnitus associated with otorrhoea of clear fluid and impaired vestibular function. CT revealed large lytic lesions of the petrous bone. T1-weighted MRI before and after gadolinium confirmed the presence of a mixed tumour of the petrous bone with marked uptake of contrast medium. Spin echo images demonstrated the absence of extradural extension, and the patency of the arterial and venous network, therefore enabling differential diagnosis from extensive glomus jugulare tumours.