Foramen magnum morphological abnormalities as a novel imaging feature of Joubert syndrome

Mika Shapira Rootman 1 Charles Raybaud 2 Patrick Shannon 3 Grace Yoon 4 David Chitayat 5 Susan Blaser 2
1Diagnostic imaging, Schneider's Children hospital, Israel
2Department of Diagnostic Imaging, Division of Neuroradiology, The Hospital for Sick Children, University of Toronto, Canada
3Pathology & Lab Medicine, Mount Sinai Hospital, Canada
4Clinical and Metabolic Genetics, The Hospital for Sick Children, Canada
5Medical Genetics & Microbiology, Mount Sinai Hospital, Canada

BACKGROUND AND PURPOSE: The most distinctive imaging feature of Joubert syndrome is the ‘molar tooth’ deformity representing the appearance of the mesencephalon on the axial view. This finding is often difficult to discern, particularly on fetal MRI studies due to small size and limited resolution. In this study we aimed to identify additional features that might assist in the radiological diagnosis of Joubert, and focused on the appearance of the foramen magnum.

MATERIALS AND METHODS: The imaging and medical records of 62 patients with confirmed ‘molar tooth’ deformity were reviewed, including 7 cases of fetuses. The foramen magnum in each subject was evaluated by 2 pediatric neuroradiologists for its configuration and categorized as ‘normal’ or ‘abnormal’ (ectatic, keyhole/diamond or meningocele). Additional posterior fossa anomalies as small rotated vermis and cystic-like enlargement were evaluated as well. Genetic mutations were retrieved when available.

RESULTS: Abnormal configuration of the foramen magnum was detected in 38/62 (61.2%) of patients, with the keyhole/diamond shape being the most common variant representing 25/38 (65.7%) of all anomalies. Among the 7 fetal cases, the configuration of the foramen magnum was always abnormal, with 5/7 (71.4%) being keyhole/diamond and 2/7 (28.5%) representing true foramen magnum meningocele. The likelihood and severity of foramen magnum abnormalities increased with the presence of additional posterior fossa anomalies.

CONCLUSION: Variations in shape of the foramen magnum are common in Joubert syndrome, detected in both pre and postnatal imaging. This additional marker could potentially assist in the correct diagnosis, particularly in the fetus.

Mika Shapira Rootman
Mika Shapira Rootman