Vertebral pneumatocyst

A several month history of cervical pain. Plain X-rays showed a discrete lucent lesion.

The patient presented with a history of pain in her neck of several months' duration. Plain radiographs showed degenerative changes of the cervical spine but also a well-defined lytic lesion in the fifth cervical vertebral body (Fig. 1). This raised concern of a lytic metastasis or multiple myeloma. A bone scan showed generalised uptake in the lower cervical spine and lower lumbar spine, but no discrete areas of increased or decreased uptake (Fig. 2). MRI showed that the lesion was of low uptake on T1- and T2-weighted images. CT showed that the lesion contained air: in keeping with a pneumatocyst. Her pain was most likely to be due to degenerative disease.

Intraosseous pneumatocyst (IP) is a relatively rare benign condition which mainly involves the ilium and sacrum around the sacroiliac joints. It is also seen in vertebral bodies usually in close proximity to endplates or facet joints. Other less common sites such as the spinous process, clavicle or humeral head have also been described. It is important to remember that IP is usually asymptomatic and an incidental finding.

IP is seen as a well-defined radiolucent area with sclerotic margin on plain film. On standard radiographs metastasis, multiple myeloma or rarer neoplasms such as osteoblastoma may initially be considered. The thin rim of sclerosis in combination with the diagnosis of gas on CT or MR images lead, as in this case, to the correct diagnosis.

On MRI, IP is seen as areas of low signal on both T1- and T2-weighted sequences. Similar signals can be seen with areas of sclerosis and haemorrhage, both in the acute stage (deoxyhaemoglobin) and later on as haemosiderin. CT is the imaging modality of choice in the diagnosis of IP, showing gas attenuation within a well-defined area surrounded by sclerosis. More than 90% of the gas is nitrogen. Different theories (such as ischaemic changes, extension of an intervetebral vacuum phenomenon, and repeated endplate microfractures) have been suggested with regards to the origin of the IP. However the exact aetiology and natural course is not clearly understood. Recognition of IP is important in order to avoid unnecessary biopsies and follow up.