Journal of Neuro-Ophthalmology:
Magnetic Resonance Findings in the Pregeniculate Visual Pathways in Leber Hereditary Optic Neuropathy
van Westen, Danielle MD, PhD; Hammar, Björn MD, PhD; Bynke, Gunnel MD, PhD
Section Editor(s): McCulley, Timothy J MD
Department of Neuroradiology (DvW), Center for Medical Imaging and Physiology, Skåne University Hospital, Lund, Sweden; Department of Diagnostic Radiology (DvW), Lund University, Lund, Sweden; and Neuro-Ophthalmology Unit, Department of Ophthalmology (BH, GB), Skåne University Hospital, Lund, Sweden.
Supported by the Skåne County Research and Development Council, the Swedish Research Council, Kronprinsessan Margaretas Arbetsnämnd för synskadade (Crown Princess Margareta's Foundation for the Visually Handicapped), Synskadades Väl i Östergötland, and Carmen och Bertil Regnérs fond (Carmen and Bertil Regnérs Foundation) and Lund University Hospital funds.
Conflict of interest: None.
Address correspondence to Danielle van Westen, MD, PhD, Department of Radiology, Lund University Hospital, SE-221 85 Lund, Sweden; E-mail: email@example.com
Two relatives, a 61-year-old man and the 21-year-old grandson of his sister, suffered from bilateral visual loss and were diagnosed with Leber hereditary optic neuropathy. In both cases, the diagnosis was molecularly confirmed with the 11778 mitochondrial mutation. MRI showed increased T2 signal not only in the optic nerves and chiasm but also in the optic tracts, extending to the lateral geniculate bodies. To our knowledge, the latter finding has not been described previously.
Case 1: A 61-year-old man, complained of painless decline in vision in both eyes. Three months later, visual acuity was counting fingers (CF) at 1 m bilaterally, kinetic perimetry revealed large central scotomas, and funduscopy was normal. Genetic analysis revealed the mitochondrial DNA 11778 mutation consistent with the diagnosis of Leber hereditary optic neuropathy (LHON). MRI of the brain and orbits performed 1 month later demonstrated increased T2 signal centrally in moderately enlarged prechiasmal optic nerves, optic chiasm, and optic tracts (Figs. 1, 2). Similar signal increase was found on the short time inversion recovery sequence (STIR). No contrast enhancement was present. Repeat MRI examination 9 months later revealed persistent high T2 signal in atrophic retrobulbar optic nerves, chiasm, and optic tracts (Figs. 1, 2). His final visual acuity remained at CF in both eyes.
Case 2: A 21-year-old man is the maternal grandson of the sister of Case 1. He experienced decreased vision in his right eye with visual acuity of CF at 1.5 m, loss of color vision, and a central scotoma on visual field testing. Three months later, the visual acuity in his left eye decreased to CF. Six months after the initial visual loss, MRI of the brain and orbits demonstrated increased T2 signal centrally in the prechiasmal optic nerves, optic chiasm, and optic tracts (Figs. 3, 4). There was no contrast enhancement. Repeat MRI 6 months later revealed that the signal abnormality was still present (Figs. 3, 4). His final visual acuity was CF 1 m in both eyes.
To the best of our knowledge, this is the first report of signal changes detected on MRI in the optic tracts of patients with LHON. Anatomic changes in LHON include reduction of the optic nerve diameter, central axonal loss, and sometimes minimal inflammatory changes (1-3). In a whole brain specimen from a patient with the classical clinical profile of LHON, severe loss of retinal ganglion cells and axons was present as well as central demyelination in the optic nerves chiasm and optic tracts (4). Thus, LHON seems to affect the retinal ganglion cells along the whole length of the axon. In our patients, signal changes in the optic tract in subacute LHON were accompanied by enlargement of the structures involved, possibly due to edema with or without axonal swelling. In the chronic phase, signal changes persisted, most likely representing gliosis.
Considering that histopathologic studies have shown involvement of the retinal ganglion cell axon along its entire length, it is remarkable that MRI demonstration of the optic tract involvement in LHON has not been reported previously. Generally, no abnormalities are seen on MRI of the brain and orbits in patients with LHON (5-7). A few reports document T2 and STIR signal abnormalities several months to years after the onset of visual loss (6-10). Signal changes in the optic chiasm have been reported twice (11,12). We reviewed the findings in these reports, but adequate imaging of the optic tracts was not performed.
Failure to detect optic tract involvement in LHON may be due to lack of awareness and failure to use an examination designed to image the optic tracts. In case 1, such images were accidentally obtained because the patient was evaluated with a combined orbit and pituitary protocol. Case 2 was subsequently examined with the same protocol. The frequency of our finding can be established only when dedicated imaging of the optic tracts is performed routinely in patients with LHON.
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