INTERESTING IMAGE

FDG–PET Imaging in the Investigation of Homonymous
Hemianopia in a Patient With MELAS Syndrome
Martin J. Shelly, MB BCh BAO, BMedSc, MRCSI,* Peter Kelly, MB BCh BAO, MRCPI,†
and Martin J. O’Connell, MB BCh BAO, MRCPI*

Abstract: Mitochondrial myopathy, encephalopathy, lactic acidosis,
and stroke-like episodes (MELAS) syndrome is a rare congenital
disorder of mitochondrial DNA. Patients with MELAS syndrome
present with a range of clinical symptoms including headaches,
hearing loss, visual defects, and hemiparesis. We report a case of a
previously asymptomatic 21-year-old male who presented with
recurrent headache, seizures, and right homonymous hemianopia.
Investigations included brain MRI, which indicated bilateral occipital white matter and cortical signal abnormality and fluorodeoxyglucose (FDG)–PET brain imaging which demonstrated markedly
reduced metabolism in the occipital lobes. The patient was treated
with corticosteroids and coenzyme Q and his clinical symptoms
have improved.

Key Words: MELAS syndrome, FDG–PET brain, MRI brain,
homonymous hemianopia, metabolism
(Clin Nucl Med 2007;32: 479 – 480)

REFERENCES

Received for publication October 18, 2006; revision accepted February 26,
2007.
From the *Mater PET/CT Centre, Department of Radiology, Mater Misericordiae University Hospital, Eccles St., Dublin 7, Ireland; †Department
of Neurology, Mater Misericordiae University Hospital, Eccles St.,
Dublin 7, Ireland.
Reprints: Dr. Martin Shelly, 59 Belgrove Park, Clontarf, Dublin 3, Republic
of Ireland. E-mail: martinshelly@eircom.net.
Copyright © 2007 by Lippincott Williams & Wilkins
ISSN: 0363-9762/07/3206-0479

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Clinical Nuclear Medicine • Volume 32, Number 6, June 2007

FIGURE 1. A, Axial FDG-PET 3D brain study on a 21 male with homonymous hemianopia demonstrates bilateral marked reduction in occipital cortex metabolism in a symmetrical distribution. There is very limited data published on the metabolic
appearances of MELAS syndrome. Early reports showed a marked decrease in glucose utilization in all grey structures, with a
preponderance of metabolic alterations in posterior cortical regions and thalamus, with a relative sparing of anterior cortical
areas and basal ganglia.1,2 Cortical hypometabolism may also reflect dysfunction of associated white matter tracts. The clinical
symptoms in MELAS syndrome are the result of a mitochondrial cytopathy affecting neurons or glia.2 Cortical hypermetabolism has also been described3 and this may reflect early disease states where glucose uptake in the cortex is increased, but oxidative metabolism is impaired due to the abnormal function of neuronal mitochondria. B, Axial MR diffusion sequence
(B1000) of the brain at the same level as A demonstrates diffuse cortical and white matter signal hyperintensity in the medial
left occipital lobe.

FIGURE 2. A, Left parasagittal FDG-PET 3D brain image demonstrates diffuse hypometabolism in the left occipital cortex,
which extends into the left posterior parietal cortex. B, Left parasagittal FLAIR MR brain sequence at the same level demonstrates diffuse cortical and grey–white matter junction signal abnormality in the occipital lobes with an associated area of signal change in the parietal cortex superior to the parieto-occipital fissure. MRI indicates predominantly grey matter changes,
but there is also a small focal area of high signal change within the posterior aspect of the left cerebellar hemisphere white
matter. Of note, cerebellar metabolism at FDG-PET was normal (A). The most commonly described MR findings in MELAS
syndrome include multiple cortical and subcortical infarct-like lesions which are not confined to the vascular territories4,5 and
calcification of the basal ganglia.6 Infarct-like lesions are distributed throughout all areas of the brain, but are maximally concentrated in the occipital and parietal lobes.6,7 Swelling of the cortex with intracortical hyperintense bands in T2-weighted
images,8 representing acute laminar necrosis, has also been reported. Generalized cerebral and cerebellar atrophy is only
found in severe disease.6

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