Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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October 10, 2024
Ectopic Choroid Plexus in Chiari II Malformation
- Background:
- Chiari type II malformation is a developmental anomaly characterized by myelomeningocele with herniation of the medulla, fourth ventricle, and cerebellar vermis through the foramen magnum. It is associated with multiple spinal, cerebral, and cranial vault abnormalities.
- To the authors' knowledge, less than 5 cases of ectopic choroid plexus in Chiari type II malformations have been reported. It has been described to arise as a fibrovascular nodule located caudal to the distal tip of herniated cerebellar tissue.
- This is thought to be a result of disruptions in the formation of the pontine flexure during neurodevelopment.
- Clinical Presentation:
- Incidence: Rare finding in patients with Chiari type II malformation with profound hindbrain herniation. Typically asymptomatic in most patients. Can present with new-onset, typically motor, neurologic symptoms in patients with evolving nodules.
- Location: Most commonly develops caudal to displaced cerebellar vermis at the cervico-medullary junction. Other reported locations include the dorsal surface of the vermis.
- Diagnostic Features/Findings:
- Nodular tissue arising from the tail of the displaced cerebellar vermis.
- MRI characteristics: T1 hypointense to isointense, homogeneously enhancing; T2 hypointense, does not demonstrate diffusion restriction.
- Differential Diagnosis:
- Hemiangioblastoma – Benign neoplasm of spinal vasculature. Typically presents as a predominantly intramedullary mass, usually with some extramedullary component. T1 variable intensity with strong enhancement, T2 iso- to hyperintense.
- Spinal ependymoma – Arises from ependymal cells of the central canal; most common intramedullary spinal cord neoplasm in adults. T1 hypo- to isointense, T2 hyperintense, intramedullary mass usually demonstrates homogeneous enhancement.
- Spinal ganglioglioma – Rare intramedullary tumor primarily associated with pediatric populations. Lesions classically demonstrate dual/mixed T1 intensity with patchy enhancement and T2 hyperintensity.
- Subependymoma- Inferior fourth ventricle lesion with minimal or no enhancement.
- Treatment:
- Ectopic choroid plexus is a benign finding. One reported case with progressive neurologic deficits may have been secondary to reactive inflammatory changes.
- Further intervention is not recommended for asymptomatic patients. Surgical resection is indicated for patients with new neurologic deficits secondary to growth or surrounding reactive changes of the lesion, or if the lesion demonstrates findings concerning for a neoplastic process.
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