Globus pallidus and substantia nigra hypointensities on T2*-weighted imaging in MELAS

Abstract

We present a 48-year-old mother [with history of seizures, migraine, diabetes mellitus, neurosensory hearing loss, short stature, cognitive deficit, and ataxia, and onset of stroke-like episodes 3 years after initial magnetic resonance imaging (MRI)] and her 20-year-old son (with history of one strokelike episode at the moment of the initial MRI, and another stroke-like episode 3 months later, in absence of other signs) with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS, m.3243A [G tRNALeu[UUR] mutation), both showing on computed tomography (CT) bipallidal microcalcifications and on initial 3-T T2*-weighted MRI (TE = 13 ms, TR = 475 ms) large bilateral hypointensities in the pallidum and the substantia nigra (Fig. 1). Basal ganglia showed normal intensities on T1-weighted and fluid-attenuated inversion recovery (FLAIR) imaging, and very slight hypointense (i.e., nearnormal) signal on T2-weighted imaging (Fig. 1). One strokelike lesion (accompanying stroke-like symptoms) was seen on initial MRI in the son, and another stroke-like lesion occurred 3 months later, and the mother presented strokelike lesions 3 years after the initial MRI (Fig. 2). Both patients also showed cerebral and cerebellar atrophy, and slight bilateral posterior leukoencephalopathy on MRI (Fig. 2). MRI follow-up (3 years in the mother, and 3 months in the son) did not show evolution of the T2*-weighted hypointensities in the pallidum and the substantia nigra. Radiological abnormalities (sometimes absent or discrete, especially in the early stage of the disease) encountered in MELAS include cerebral and cerebellar atrophy, basal ganglia signal changes, stroke-like lesions, and leukodystrophy. Extensive calcifications are the most frequently encountered basal ganglia abnormalities in MELAS, most frequently described on CT and only rarely on MRI in the literature [1]. Basal ganglia calcifications in our two patients were discrete on CT. The extent of the MRI abnormalities, when compared with CT, may be explained by the magnetic susceptibility effect of T2*weighted imaging (potentially exaggerated by the highfield 3-T MRI used in our patients) and/or the presence of microscopic calcium and iron deposition [2, 3]. Both calcium and iron deposition in the globus pallidus have been demonstrated earlier on autopsy in MELAS [2]. T2and diffusion-weighted MRI changes and necrotizing lesions on autopsy have been reported in the substantia nigra in another mitochondrial syndrome, i.e., Leigh syndrome [4, 5]. In a general population, incidence of basal ganglia calcifications on CT scan varies between 0.6 and 0.8 % [6, 7]. Incidence increases with increasing age [7, 8]. In the elderly, basal ganglia calcifications are encountered in 38.7 % of patients on CT scan, with the globus pallidus as the most frequently involved structure [9]. The precise agematched incidence, the MRI-based incidence of age-related basal ganglia calcifications, and the pathophysiology explaining the predominant involvement of certain substructures (e.g., the pallidum in our MELAS patients and in the elderly) are unknown. When MELAS is suspected clinically, T2*-weighted MRI imaging (and thus not only CT scan) may be an interesting additional radiological tool to detect discrete calcium and/or iron deposition, especially in young patients (in whom age-related basal ganglia calcifications are less D. Renard (&) C. Campello A. Le Floch G. Castelnovo G. Taieb Department of Neurology, CHU Nimes, Hopital Caremeau, Place du Pr Debre, 30029 Nimes Cedex 4, France e-mail: dimitrirenard@hotmail.com