Extracranial meningioma
Extracranial meningiomas, also known as primary extradural meningiomas are a form of ectopic meningioma, are a rare location-specific type of meningioma that arise outside the dural covering of the brain and spinal cord. They are essentially extracranial tumors, most often occurring in the head and neck, most commonly in the sinonasal tract, temporal bone and ear, and in the scalp.
Primary intraosseous meningioma is a term used to describe a subset of these extradural meningiomas that arise in bone .
Terminology
Extradural meningiomas do not have connections to the dura or any other intracranial structure , while secondary extradural meningioma refers to those intradural meningiomas with extradural extension and/or metastasis.
Epidemiology
Rarely, meningiomas can occur extracranially from ectopically located arachnoid cell rests (2%). Sometimes an extracranial meningioma can occur as an extension of small intracranial meningioma through skull base foramina or a diploic space. No sex predilection.
Clinical presentation
Symptoms will rely on the region where the meningioma appears.
Pathology
Theories assume that extradural meningiomas arise from the meningothelial cells that were entrapped within the skull sutures or fracture lines either congenitally or post-traumatic, respectively. Cutaneous meningiomas are believed to arise due to a defect in the neural tube closure which led to entrapped meningocytes in subcutaneous tissue. Other theories postulate that meningiomas can arise from multipotent mesenchymal cells.
Classification
Lang et al. classified extracranial meningiomas as:
- type I: purely extra calvarial
- type II: purely calvarial
- type III: calvarial with extra calvarial extension
Type II and Type III tumors were further categorized as convexity (C) or skull base (B) lesions. They also found patients with IIC or IIIC have lesser recurrence rates compared to IIB or IIIB tumors.
Location
Extracranial meningiomas can occur in multiple locations like paranasal sinuses, skin, orbit, temporal fossa and oral cavity . Other rare sites include the nasal cavity, salivary glands, scalp and carotid artery bifurcation.
Radiographic features
They are similar to intracranial meningiomas regarding morphology and enhancement.
CT
- calcifications and intense enhancement
- hyperostosis, remodeling and expansion of the affected region of the skull with or without extra calvarial soft tissue mass
- purely osteolytic skull lesions are also reported and believed to be of worse prognosis, particularly if associated with a soft tissue component
MRI
Signal characteristics are similar to any meningioma
- T1: hypointense
- T2: mixed signal intensity; calcifications appear as signal voids
- C+ (Gd): intense homogeneous enhancement
MRI may detect a small intracranial component if present.
Treatment and prognosis
Extensive surgical resection if possible, as incomplete removal may lead to recurrence. More liable to malignant degeneration (11%) than intradural meningioma.
Differential diagnosis
The differential diagnosis of these tumors is wide and based on their location, but includes:
