An intraosseous pseudomeningocele is an intradiploic CSF collection communicating with the subarachnoid space.
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Epidemiology
Intraosseous pseudomeningoceles are rare sequelae of skull fractures of traumatic or iatrogenic etiology occurring in infants and young children. They can be seen in any location, however, most cases are described in the occipital bone.
Clinical presentation
These lesions are usually asymptomatic, although they may progressively grow. Non-specific symptoms, such as headache, may also be present. Varied presentation and the long time span between the trauma and the formation of the pseudomeningocele may lead to misdiagnosis.
Pathology
The proposed mechanism for the development of intraosseous pseudomeningoceles involves a fracture of the inner table of the skull and an associated dural tear, leaving the outer table intact. The arachnoid prolapses past the fracture line into the intradiploic space and the constant CSF pulsations lead to expansion of the intradiploic space and remodeling of the bone. It is hypothesized that the strong muscle cover adjacent to the outer table of the occipital bone and the thickness of the bone prevent the development of a growing skull fracture, with a complete bony defect.
Radiographic features
CT
Brain CT shows discontinuity of the inner table of the bone and widening of the intradiploic space, filled with hypodensity.
MRI
Brain MRI reveals an expansile intradiploic cavity, presenting with signal similar to CSF on all sequences. The collection is seen to communicate with the subarachnoid space.
Treatment and prognosis
Surgical indication and management are controversial, as many patients remain asymptomatic whilst others develop delayed complications, such as hydrocephalus. The primary aim of surgery, if undertaken, is to close the dural defect, followed by cranioplasty.
Differential diagnosis
- congenital intradiploic arachnoid cyst: generally multiple, in the paramedian occipital and parietal region and usually found incidentally late in life
- leptomeningeal cyst: same pathogenesis as a pseudomeningocele, but generally arachnoid adhesions are formed and prevent free communication of the cyst with the subarachnoid space. Therefore, this is considered a non-communicating pseudomeningocele.
See also