Causes of Anterior vs Posterior Vermian Syndrome
The primary distinction between anterior and posterior vermian syndromes lies in their etiologies: anterior vermian syndrome is predominantly caused by vascular events, metabolic disorders, and toxins, while posterior vermian syndrome is typically caused by genetic/developmental abnormalities, congenital infections, and malformations.
Anterior Vermian Syndrome
Vascular Causes
- Arteriovenous malformations (AVMs) affecting the anterior vermis 1
- Vermian strokes, particularly those affecting the anterior vermis 2
- Hemorrhagic events in the anterior cerebellar region 1
Toxic/Metabolic Causes
- Alcohol-related cerebellar degeneration (preferentially affects anterior vermis)
- Anticonvulsant medications (particularly phenytoin)
- Chemotherapeutic agents (particularly 5-fluorouracil)
Other Causes
- Paraneoplastic cerebellar degeneration
- Nutritional deficiencies (thiamine deficiency)
- Infectious/post-infectious cerebellitis affecting anterior vermis
Posterior Vermian Syndrome
Genetic/Developmental Causes
- Mutations in microtubule component genes (TUBB) and associated proteins (KATNB1, CENPJ) 3
- Autosomal recessive disorders affecting O-glycosylation of α-dystroglycan 3
- GPSM2 mutations (Chudley–McCullough syndrome) 3
- EML1 mutations (associated with ribbon-like heterotopia with vermian agenesis) 3
- LAMA2 mutations (causing limited cobblestone cortex with vermian abnormalities) 3
- DIS3L2 mutations (Perlman syndrome) 3
- Neurofibromatosis type 1 3
- Joubert syndrome (characterized by hypoplasia or complete agenesis of the cerebellar vermis) 4, 5
Congenital Infections
- Cytomegalovirus (CMV) (accounts for 12-30% of cases with vermian involvement) 3
- Toxoplasmosis (associated with vermian hypoplasia) 3
- Syphilis 3
- Varicella zoster virus 3
- Zika virus 3
Malformations
- Dandy-Walker malformation (posterior vermian agenesis with cystic dilatation)
- Vermian agenesis without posterior fossa cyst 6
- Rhombencephalosynapsis (fusion of cerebellar hemispheres with absent vermis)
Clinical Manifestations
Anterior Vermian Syndrome
- Prominent gait and truncal ataxia
- Dysarthria
- Nystagmus
- Less cognitive/behavioral involvement
Posterior Vermian Syndrome
- Developmental delay 3
- Complex oculomotor dysfunction 4, 6
- Abnormal vestibulo-ocular reflex cancellation
- Impaired smooth pursuit
- Defects in saccade initiation
- Truncal ataxia 3, 4
- Behavioral/emotional symptoms (particularly in Posterior Fossa Syndrome) 2
- Episodic hyperpnea and apnea (in Joubert syndrome) 4, 5
Diagnostic Approach
Imaging
- Brain MRI is the gold standard for evaluating vermian abnormalities 3
Additional Testing
- Genetic testing (chromosomal microarray analysis, next-generation sequencing) for suspected genetic causes 3
- Infectious disease workup (PCR for CMV and other congenital infections) 3
- Metabolic screening (particularly very long chain fatty acids for peroxisomal disorders) 3
Clinical Pearls and Pitfalls
- Pearl: The vermis has a distinct embryological development compared to cerebellar hemispheres, making it vulnerable to specific developmental abnormalities
- Pitfall: Not all vermian abnormalities present with classic cerebellar symptoms; behavioral, cognitive, and respiratory symptoms may predominate
- Pearl: Posterior vermian abnormalities are more commonly associated with genetic syndromes and developmental disorders
- Pitfall: Vermian hyperplasia can occur in a subset of patients with autism spectrum disorders, not just hypoplasia 7
- Pearl: Posterior Fossa Syndrome can occur after both surgical and non-surgical (e.g., stroke) damage to the vermis 2