Ataxia, hypoplastic vermis and keyhole connection sign: is it the variant form of Dandy-Walker complex?
- Correspondence to Dr Osama S M Amin,
A 12-year-old girl has a progressive instability of stance and gait since the age of 2 years. She demonstrates mild mental subnormality and signs of cerebellar incoordination. A diagnosis of an ataxic form of cerebral palsy was made at the age of 3 years. When she was 9 years old, she started to develop occasional vomiting and headache which were ascribed to ‘hydrocephalus’. Accordingly, shunting surgery was performed (figure 1). Both headaches and vomiting remarkably improved; however, the cerebellar dysfunction remained. Her up-to-date brain MRI is shown (figure 2).
The symptomatology and brain imaging do not categorise the girl as having Dandy-Walker malformation or Dandy-Walker mega cisterna magna; she fits the ‘variant form’ of Dandy-Walker complex.1 This form is very heterogeneous and results in a multitude of phenotypes.2 The brainstem per se and the lateral ventricles are normal and the posterior fossa is normal or typical mildly enlarged. The midline vermis is hypoplastic and the cisterna magna communicates, through an enlarged vallecula, with the posterior/inferior aspect of the fourth ventricle forming the so-called keyhole connection sign. Therefore, posterior fossa cystic spaces appear to be enlarged.3
Supratentorial malformations are uncommon and hydrocephalus is found in 25% of patients only. The typical ‘torcular-lambdoid inversion sign’ of Dandy-Walker malformation is not encountered in the variant form.
Patients with less severe symptoms and mild anomalies usually hold a good prognosis. The presence of severe malformations (including multiple intracranial and extracranial anomalies) portends a gloomy outlook.
Dandy-Walker complex-variant form defines patients who do not fit the fully-fledged Dandy-Walker malformation or Dandy-Walker mega cisterna magna categories and represents a less severe form of this ciliopathy with a relatively good prognosis.
Characteristically, torcular-lambdoid inversion sign of Dandy-Walker malformation is not encountered in the variant form. The posterior fossa may be mildly enlarged and this, together with enlarged posterior fossa cystic spaces, may prompt the neurologist to think of hydrocephalus and unnecessary shunting surgery may ensue.
Coexistent intracranial and extracranial anomalies are uncommon but their presence portends a poor prognosis.
Competing interests None.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.