Rhombencephalosynapsis
- Rhombencephalosynapsis is a rare developmental malformation of the cerebellum with an unknown etiology and pathogenesis. It is characterized by abscence of the vermis and dorsal fusion of the cerebellar hemispheres, dentate nuclei, and superior cerebellar peduncles.
- The majority of patients are nonsyndromic. However, rhombencephalosynapsis is a key feature of Gómez-López-Hernández syndrome (parietal alopecia, trigeminal anesthesia, and craniofacial dysmorphic signs) and may be seen in patients with associated VACTERL (vertebral anomalies, anal atresia, cardiovascular anomalies, tracheoesophageal fistula, renal anomalies, and limb defects).
- Clinical manifestation and prognosis depend on posterior fossa findings and associated supratentorial anomalies. These anomalies include hydrocephalus (often from aqueductal stenosis), dysgenesis of corpus callosum, absence of septum pellucidum, and fusion of the thalami. Though rare, extracranial abnormalities involve the musculoskeletal, urinary, cardiac, and respiratory systems. Common symptoms include mental retardation, ataxia, spasticity, and epilepsy. Patients may be asymptomatic if rhombencephalosynapsis is an isolated finding.
- Key Diagnostic Features:
- Complete agenesis or hypogenesis of the cerebellar vermis (indicated by a diamond-shaped 4th ventricle) with fusion of the cerebellar hemispheres, dentate nuclei, and superior cerebellar peduncles.
- Other indicators include a flat-based cerebellum, large corpus medullare, and horizontal folial orientation with no vermis present.
- DDx: None. Findings are pathognomonic of this entity.
- Rx:
- No medical management is required for isolated cases of rhombencephalosynapsis.
- Surgical management may be needed in cases with associated anomalies; presence of hydrocephalus may require the placement of a ventriculoperitoneal shunt.
