A JOURNAL OF NEUROLOGY SCIENTIFIC COMMENTARY

Rhombencephalosynapsis: new findings in a larger study Rhombencephalosynapsis is a developmental midline defect affect-ing the cerebellar vermis. The absence of the vermis in rhomben-cephalosynapsis may be compared to the other condition in which the vermis is largely absent. In Joubert syndrome, the cerebellar hemispheres are close to normal in volume; the intervening vermis is small and much shortened, leaving a gap between the cerebellar hemispheres. Although the vermis may also be totally absent in rhombencephalosynapsis, remnants such as the nodule may often be found in their normal place with respect to the adjoining hemi-spheres. Allowing a simplification, one can describe the vermis in Joubert syndrome as shortened and in rhombencephalosynapsis as narrowed. The debut of the rhombencephalosynapsis story is credited to Obersteiner in 1916 with a detailed case report entitled ‘Ein Kleinhirn ohne Wurm ’ (‘A cerebellum without vermis’) describing the autopsy findings in a 31-year old male. The original study is still worth reading for its wealth of detail such as absence of the mesencephalic trigeminal nucleus and misrouting of tracts at the lower mesencephalic level. Over 100 cases have since been pub-lished, mostly as case reports or small series. A review lists 58 published cases before 2005 (Barth, 2008). Hydrocephalus due to aqueductal stenosis is often present at birth. Other cerebral malformations typically affecting the midline may be found includ-ing aplasia of the septum pellucidum, fusion of the fornices and holoprosencephaly. Morphological studies reported by Pasquier et al. (2009) in 40 foetuses after medical termination of pregnancy showed fusion of colliculi, forking and/or atresia of the aqueduct, fusion of the thalami, callosal agenesis, lobar holoprosencephaly and neural tube defects as associated findings. Attention was drawn to the frequent occurrence of ‘Vertebral anomalies, Anal atresia, Cardiovascular anomalies, Trachea-oesophagEal fistula, Renal anomalies, Limb defects ’ (VACTERL) as associated findings. The cognitive outcome in patients with rhombencephalosynapsis may be normal; ataxia was the most frequent physical finding in a series of non-syndromic rhombencephalosynapsis (Poretti et al., 2009). Two syndromes may be seen in association with rhombence-phalosynapsis: Gómez–López-Hernández syndrome (MI