Skull base and craniocervical bone pneumatisation: two case reports of differing presentations and a review of the literature.

We report two patients with increased central skull base and craniocervical junction bone pneumatisation complicated by extra-osseous gas. One patient presented with symptoms of increasing nasal blockage and 'sinus pressure' on a background of extensive nasal polyposis. He was subsequently found to have a history of repeated Valsalva's manoeuvre, the cessation of which resulted in a rapid decrease in the amount of extra-osseous gas on imaging. The second patient presented following a minor head trauma with dysarthria from a hypoglossal nerve palsy and neck pain, with extensive intra- and extra-cranial gas including within the spinal canal (pneumorrhachis). These radiological findings have been reported previously in patients with Eustachian tube dysfunction and/or activities leading to frequently raised middle ear pressures. We review the possible aetiologies, reported risk factors, and the range of associated imaging abnormalities that may be encountered with this rare appearance.