Causes and association with dural ectasia
Spinal dysraphisms, which include meningocele, are accompanied in most cases by dural ectasia—widening of the dural sac.
Main causes of dural ectasia:
- Systemic connective tissue disorders: neurofibromatosis (neurofibromatosis), Marfan syndrome (Marfan syndrome), Ehlers-Danlos syndrome (Ehlers-Danlos syndrome). These conditions can provoke both local and generalized ectasia.
- Erosive arthropathies: a striking example is ankylosing spondylitis (Bechterew's disease). In this case, ectasia can form specific "pouches" invading the vertebral bodies and arches (on MRI, this manifests as scalloping of the posterior vertebral surface against the backdrop of a typical "bamboo spine").
- Idiopathic factors: a significant proportion of lesions occur without an identifiable cause.
Anterior sacral meningocele
Anterior sacral meningocele (Anterior Sacral Meningocele) is a complex presacral cystic mass (uni- or multilocular) filled with CSF. It directly communicates with the intraspinal subarachnoid space via a large eccentric defect in the anterior sacral wall. It is often associated with agenesis of the lower sacrum and coccyx.
Radiological signs:
- Radiography: the bone defect gives the remaining sacrum a pathognomonic "scimitar" appearance (scimitar appearance).
- MRI and CT: a pelvic mass is visualized. MRI is the gold standard as it reliably demonstrates communication between the cyst and the widened sacral canal.
There is also a variant known as occult intrasacral meningocele (Occult intrasacral meningocele). In this condition, the sacral canal is widened and the dural sac terminates below the normal level, but there is no anterior bone defect or extension of the cyst into the pelvic cavity.
Thoracic forms of meningocele
In the thoracic spine, two main types of meningocele are distinguished, which have completely different clinical and radiological presentations:
- Lateral thoracic meningocele:
On radiographs, it appears as a paravertebral mass. Usually, this is a solitary cyst, most frequently located on the right side. In 70–85% of cases, the pathology is associated with neurofibromatosis. Characteristic concomitant signs include angular kyphoscoliosis with the apex directed toward the cyst, and erosion of the intervertebral foramen margins due to pressure.
- Anterior thoracic meningocele with ventral spinal cord herniation:
A rare but important cause of chronic thoracic myelopathy of unclear etiology in adults. The spinal cord is displaced anteriorly and contacts the vertebral body or intervertebral disc. The typical location is the T2–T8 level (most frequently T6). Best recognized on midsagittal MRI slices.
MRI presentation of anterior spinal meningocele
Diagnosis of anterior thoracic meningocele can be extremely challenging. The lesion is often small and poorly differentiated on standard MRI scans. The pathology can easily be mistaken for an intradural arachnoid cyst displacing the cord or a dorsal thoracic arachnoid web (dorsal thoracic arachnoid web).
Optimal protocol: volumetric, heavily T2-weighted high-resolution sequences (CISS, FIESTA, 3D TSE) with mandatory multiplanar reconstructions must be used.
Key radiological findings:
- On sagittal T2-weighted images, the spinal cord is intimately apposed to the disc protrusion or vertebral body.
- Below the level of tethering (caudally), a fusiform syringomyelic cavity (syrinx) may be visualized.
- On axial slices, the shape of the spinal cord is deformed, changing from a normal rounded contour to a triangular one.
- The spinal cord appears densely apposed to the dura mater anteriorly.
- Anterior and caudal to the tethering zone, a CSF-filled dural sac is visualized.
Briefly: answers to topical questions
What are the symptoms and clinical manifestations of anterior spinal meningocele in adults?
In adults, anterior thoracic/spinal meningocele with ventral spinal cord herniation rarely serves as an explanation for chronic thoracic myelopathy of unclear etiology.
Clinical features according to sources:
- Chronic thoracic myelopathy (thoracic myelopathy) — indicated as a rare manifestation/explanation in adults.
Other specific clinical symptoms are not described in the cited sources. It is noted that the pathology is localized in the thoracic spine; the spinal cord is displaced anteriorly and contacts the vertebral body or intervertebral disc at the T2–T8 level, most commonly at the T6 level.
To remember the radiological sign of anterior sacral meningocele, use the mnemonic: an eccentric bone defect gives the sacrum the shape of a curved blade (scimitar appearance).
Class and exam questions
What is the difference between anterior sacral meningocele and occult intrasacral meningocele?
In occult intrasacral meningocele, there is no defect in the anterior sacral wall, and the cystic lesion does not extend into the pelvic cavity, remaining within the widened sacral canal.
What disease is lateral thoracic meningocele most frequently associated with?
In 70–85% of cases, lateral thoracic meningocele is associated with neurofibromatosis. It is frequently accompanied by a right-sided location and angular kyphoscoliosis.
Why is anterior thoracic meningocele difficult to diagnose on MRI?
The defect and the cyst itself can be very small. Their visualization and differentiation from a dorsal arachnoid web require special heavily T2-weighted 3D sequences (CISS, FIESTA).
What else to study on this topic
- Neuroenteric cyst and congenital vertebral segmentation anomalies
- Intraspinal arachnoid cyst: extradural and intradural forms
- Dural ectasia in Bechterew's disease (ankylosing spondylitis)
- Cystic lesion of the conus medullaris: terminal ventricle
- Chiari I malformation and associated syringomyelia
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