An intraosseous pseudomeningocele is an intradiploic CSF collection communicating with the subarachnoid space.
Intraosseous pseudomeningoceles are rare sequelae of a skull fractures of traumatic or iatrogenic ethology occurring in infants and young children. They can be seen in any location, however, most cases are described in the occipital bone.
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.
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 intradiploic space and remodelling 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.
Brain CT shows discontinuity of the inner table of the bone and widening of the intradiploic space, filled with hypodense
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.
- 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.
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- 2. Kumar R, Chandra SP, Sharma BS. Giant intradiploic pseudomeningocele of occipital bone: case report. Journal of Neurosurgery: Pediatrics. 2012 Jan;9(1):82-5.
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