Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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June 20, 2024
Idiopathic Herniation of Gyrus Rectus
- Background:
- Acquired compressive optic neuropathy from idiopathic herniation of gyrus rectus (HGR) is rare.
- Compressive optic neuropathies must be considered in the differential diagnosis of painless visual loss in the clinical context of optic atrophy and relative afferent pupillary defect. In most circumstances, compressive optic neuropathies typically present as a protracted course of gradually worsening visual loss.
- The gyrus rectus is located in the floor of the anterior cranial fossa superior to the prechiasmatic optic nerves and the optic chiasm. The posterior aspect of the gyrus rectus lies directly above the anterior aspect of the optic chiasm. Downward HGR can cause compression of the prechiasmatic optic nerve, and more a posterior herniation into the suprasellar cistern can also compress the optic chiasm.
- In our case, there were no parenchymal mass lesions. There were also no signal abnormalities in the optic nerves or the chiasm.
- Clinical Presentation:
- Common presentation is unilateral vision loss with incomplete superior altitudinal hemianopsia on visual field testing. Imaging is advised to assess the possible etiology and rule out a systemic condition like neuromyelitis optica or multiple sclerosis.
- Key Diagnostic Features:
- Compression of the prechiasmatic optic nerve from HGR with effacement of the cistern of the lamina terminalis; HGR signal is similar to the cortical gray matter on all the sequences
- Atrophy of the right optic nerve and optic chiasm; signal abnormalities in the optic nerves or the chiasm
- No parenchymal mass lesions
- Differential Diagnosis:
- Mass lesion such as neoplastic or dysplastic growth, arising from the frontal lobe.
- Treatment:
- In case of presence of a focal space-occupying lesion, surgical biopsy with or without complete excision will narrow the diagnosis. In idiopathic cases, conservative management and patient follow-up are required.
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