Skull base and craniocervical bone pneumatisation
We report two cases of 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 reported risk factors, the possible aetiologies and the range of associated imaging abnormalities that may be encountered with this rare appearance. Our first case is of a 53-year old male with skull base pneumatisation secondary to repetitive Valsalva’s manoeuvre. FIGURE 1: Coronal CT images comparing scans at presentation (a) and one performed 2 years previously (b). The clivus has completely pneumatised (arrows) in the interim. Extradural gas is seen within the adjacent cavernous sinuses (arrowheads) on the most recent CT scan. Our second case is of a 71-year old man with craniocervical bone pneumatisation who presented with complications following minor trauma. Anatomical detail has been highlighted for further educational value. FIGURE 2: Left para-midline sagittal (a), mid-line sagittal (b) and axial (c) CT images demonstrating increased pneumatisation involving the left occipital condyle (white arrowhead), the posteroinferior occipital bone (white arrow), and the left lateral mass and posterior arch of the atlas (open white arrows). There is generalised thinning of the cortices in these regions and partial opacification of the abnormal occipital condyle and atlas air cells (asterisks). The presumed post-traumatic micro-fractures in these areas has resulted in extensive surrounding extra-osseous gas, including within the epidural space of the foramen magnum (black arrow), and within the cervical spinal canal and neural exit foramen (open black arrows). Anatomical landmarks: 1. Exiting neural foramen for C3 nerves. 2. Anterior arch of C1. 3. Basion. 4. Opisthion. 5. Odontoid peg of C2.