Cerebellar Hypoplasia and Dysmorphia in Neurofibromatosis Type 1

Aims: Neurofibromatosis type 1 (NF1) is a multisystem disorder affecting the nervous system frequently. Well-documented cerebellar involvement in NF1 includes unknown bright objects and low-grade glial tumors. Literature reports on malformative cerebellar anomalies in NF1 however are scant. Methods: We retrospectively studied the clinical and neuroimaging findings of five patients (age 6–29 years) with NF1 and cerebellar anomalies. Morphological abnormalities were divided into the following two groups: (1) cerebellar hypoplasia with enlarged interfolial spaces and (2) cerebellar dysmorphia (including anomalies related to size, shape, and extension of a cerebellar hemisphere). Results: Cerebellar hypoplasia was found in two patients and cerebellar dysmorphia in three patients. In cerebellar dysmorphia, the right cerebellar hemisphere was involved in two patients, the left hemisphere in one. In all patients, the affected cerebellar hemisphere is enlarged and the interfolial spaces of its posterior part are widened. In addition, the posteromedial part is bulky (like an appendicular portion of additional cerebellar tissue) and crosses the midline in its very posterior aspect. Cerebellar symptoms were mild or even not evident whereas learning disabilities were more or less pronounced in four patients. Follow-up imaging studies over a couple of years showed stable unchanged findings. Conclusion: It is well known that children with cerebellar hypoplasia—irrespective of its origin—have an increased prevalence of neurological impairments, and individuals with NF1 have an increased prevalence of motor performance impairments and learning disabilities. It is not possible to decide whether the cerebellar abnormalities were contributory to neurocognitive deficits and motor coordination problems in our patients. We consider cerebellar hypoplasia and cerebellar dysmorphia in NF1 to be caused by a primary developmental (malformative), not a secondary acquired (disruptive) pathomechanism. Malformative cerebellar abnormalities including cerebellar hypoplasia and dysmorphia are a rare, but most likely underestimated manifestation of NF1.