Olfactory nerve hypertrophy: a clue to the presence of ipsilateral megalencephaly.

Iyer RS, et al. BMJ Case Rep 2017. doi:10.1136/bcr-2017-222488 Description A boy aged 4 years presented with refractory focal seizures since 9 months of age. The seizures involved the left side of the body and consisted of clonic movements with frequent generalisation. MRI brain showed abnormal area with poor grey-white differentiation involving the right frontal lobe, especially the basifrontal region and the temporal lobe (figure 1A,B) suggesting the presence of a frontotemporal developmental malformation. Interestingly olfactory nerve hypertrophy was also noted on the same side (figure 1C,D). Video-electroencephalogram study demonstrated concurrence of the interictal (figure 2A) and ictal data (figure 2B) with the MRI defined abnormality. An 18-fluoro-2-deoxy-D-glucose positron emission tomography/ CT of the brain showed severe right frontotemporal hypometabolism. The boy underwent a disconnection procedure involving the right frontal lobe sparing the motor cortex and the temporal lobe. Histopathology of the abnormal brain obtained during the surgery showed large atypical neurons, balloon cells, astrocytosis and neuronal heterotopia suggesting localised megalencephaly. The child is seizure-free at 6 months follow-up. Olfactory nerve hypertrophy is a morphological abnormality detected on MRI, outside the involved hemisphere. This was noted in 8 out of 30 patients (26.7%) with hemimegalencephaly in one study. The other such abnormalities occurring outside the involved hemisphere are cerebral vascular dilations and cerebellar enlargement. These abnormalities are seen more in association with hemimegalencephaly or localised megalencephaly. They are generally not seen in association with multilobar cortical dysplasia. It is sometimes difficult to differentiate between localised megalencephaly and multilobar cortical dysplasia from the MRI Olfactory nerve hypertrophy: a clue to the presence of ipsilateral megalencephaly Rajesh Shankar Iyer, Bejoy Thomas, Saleem Akhtar, Praveen Kumar Images in...