Two cases of histiocytosis X in young adults with involvement of only
the petrous bone are reported. In the first symptoms and signs consist
ed 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 confirme
d the presence of a mixed tumour of the petrous bone with marked uptak
e of contrast medium. Spin echo images demonstrated the absence of ext
radural extension, and the patency of the arterial and venous network,
therefore enabling differential diagnosis from extensive glomus jugul
are tumours.