Neuroradiology (1995) 37:440-442 9 Springer-Verlag i995 M. Shimodozono K. Kawahira N. Tanaka Received: 24 November 1993 Accepted: 23 March 1994 M. Shimodozono ( [ ~ ) . K. Kawahira 9 N. Tanaka Department of Rehabilitation and Physical Medicine, Faculty of Medicine, Kagoshima University, 1208-1, Usuki-cho, Kagoshima 890, Japan Functioning heterotopic grey matter? Increased blood flow with voluntary movement and sensory stimulation Abstract A 66-year-old woman with a right hemiplegia due to cerebral haemorrhage was found to have heterotopic grey matter in the left frontal and right frontal and parietal lobes. She had no neurological disturbance prior to the haemorrhage. Regional cerebral blood flow (rCBF) was measured by xenon-CT (Xe-CT) in the zones of heterotopic grey matter during voluntary movement and sensory stimulation of her left limbs. During voluntary movement, rCBF increased markedly in the heterotopic grey matter of the frontal lobes and the overlying cortex. During sensory stimulation, rCBF increased in the right parietal heterotopic grey matter and the overlying cortex. This strongly suggests that the heterotopic grey matter is functional. Key words Heterotopic grey matter - Xenon computed tomography 9Regional cerebral blood flow Introduction Case report Heterotopic grey matter is a rare developmental anomaly caused by disturbed migration of neuroblasts during fetal life [1-4] and usually associated with epileptic seizures and mental retardation [2, 4-7]. CT [2, 3, 8, 9], MRI [2, 6-11], positron emission tomography (PET) [12, 13], and single photon emission computed tomography (SPECT) [1, 14] have facilitated the diagnosis of heterotopic grey matter, making it detectable by means other than autopsy [4, 6-9, 11, 12, 14]. Heterotopic grey matter has never been reported to have any neuronal function other than as an epileptic focus. However, recent advances in measurement of regional cerebral blood flow (rCBF) and cerebral metabolism have enabled us to assess localised function and functional changes of the brain. We saw a patient with cerebral haemorrhage with bilateral heterotopic grey matter. No neurological deficits or seizures were present before the haemorrhage. To establish the function of the heterotopic grey matter, we studied changes in their rCBF during voluntary movement and sensory stimulation of unilateral extremities using xenon-CT (Xe-CT) [13, 15]. A 66-year-old woman was admitted for rehabilitation following a right hemiplegia caused by a hypertensive cerebral haemorrhage 4 months earlier. She had no neurological history and had led an active life until the stroke. On admission, she was alert and showed no dysphasia, visuospatial agnosia, or behavioural disturbances; she had a right hemiplegia with spasticity, synergia, brisk tendon reflexes, pathological reflexes, and moderate right sensory disturbance. The Mini-Mental State examination score was 28/30 points. The E E G showed no abnormality, even with photostimulation. CT showed a low density area in the left thalamus, extending to the corona radiata, compatible with the recent cerebral haemorrhage. Deformities of the frontal horns and three faint subcortical nodules were observed without contrast enhancement. M R I clearly demonstrated nodules in the left and right frontal lobes, and another in the right parietal lobe, isointense with the overlying cortex (Fig. 1). These were thought to represent heterotopic grey matter, because they were isodense on CT and isointense on M R I with the overlying cortex and showed no contrast enhancement. The rCBF was measured by Xe-CT [13, 15] using high-sensitivity collimation and a computer to calculate local Xe tissue saturation curves according to Kety's formula [16]. The patient inhaled 30 % Xe gas from a closed chamber for 4 min and then breathed room air for 5 rain into a trap chamber. Colour-coded images of rCBF were displayed and quantitation of rCBF of the heterotopic 441 Fig. 1 a Axial proton densityweighted (TR 2000 TE 30 ms) and b sagittal Tl-weighted (TR 500 TE 20 ms) images showing the heterotopic grey matter in both frontal lobes and the right parietal lobe (arrows), and deformity of the ventricles. The heterotopic grey matter is isointense with the overlying cortex Fig.2 a CT showing the regions of interest in the zones of heterotopic grey matters (1-3) and overlaying cortex (4-6). b-d XenonCT: b awake, resting, eyes closed; c during voluntary movement of the left limbs; and d during sensory stimulation of the left limbs. At rest the areas of heterotopic grey matter (arrows) showed the same regional cerebral blood flow (rCBF) as the overlying cortex. Voluntary movement induced an increase in rCBF in both frontal areas of heterotopia (arrows) and the overlying cortex. Sensory stimulation induced an increase in the rCBF of the right parietal heterotopic grey matter (arrow) and overlying cortex Table 1 Regional cerebral blood flow (ml/100 g tissue/min) of each region of interest (Fig.2a) under three conditions (HGM heterotopic grey matter) Right frontal HGM Right parietal HGM Left frontal HGM Right frontal cortex Right parietal cortex Left frontal cortex Rest Voluntary movement of left limbs Sensory stimulation of left limbs 31.3 28.4 34.6 11.9 26.1 29.3 37.8 26.7 42.4 42.7 18.7 43.4 32.7 39.1 29.3 31.1 45.8 29.3 grey matter and the cerebral cortex was performed by outlining the area on a display console (Fig. 2 a). We selected two CT planes, showing the heterotopic grey matter, to allow simultaneous study of rCBF in all three regions, rCBF was measured in the supine position under three different conditions: awake, resting, with eyes closed, as a control; rhythmic voluntary flexion and extension of the left wrist and ankle for 9 min; and continuous stimulation of the left forearm and calf with soft nylon brushes for 9 min. Figure 2b shows that, at rest, the rCBF of the three areas of heterotopic grey matter was nearly the same as that of the overlying cortex. During voluntary movement of the left limbs, the rCBF increased greatly in the heterotopic foci in the frontal lobes, as well as in the overlying cortex (Fig.2c, Table 1). The rCBF of the right parietal heterotopic grey matter, and of adjacent cortex, was unchanged. During sensory stimulation of the left limbs, the rCBF increased in the right parietal heterotopic grey matter and overlying cortex (Fig. 2 d, Table 1). The rCBF of the frontal heterotopic areas and the adjacent left frontal cortex was unchanged. Discussion H e t e r o t o p i c grey m a t t e r consists of a n o m a l o u s collections of n e r v e cells in s u b c o r t i c a l white m a t t e r w h o s e r a d i a l m i g r a t i o n f r o m the p e r i v e n t r i c u l a r g e r m i n a l z o n e s was a r r e s t e d [17]. P a t i e n t s with h e t e r o t o p i c grey m a t t e r u s u a l l y h a v e m i c r o p o l y g y r i a a n d pachygyria, in- 442 tractable epileptic seizures, an abnormal E E G and mental retardation [2, 3, 5-9]. Barkovich et al. [4] found five patients with heterotopic grey m a t t e r in m o r e than 20,000 M R I studies; and all of the affected patients had severe epileptic seizures and developmental delay. The four patients r e p o r t e d by Michael and M a t t a r [1] also had intractable seizures, mental retardation and develo p m e n t a l cortical malformations. Histologically, these ectopic nodules consist of abnormally large neurons and increased numbers of astrocytes and oligodendrocytes, with minimal architectonic stratification. A b n o r m a l l y located neurons in heterotopic grey m a t t e r have aberrant axonal and dendritic connections with the surrounding brain tissue and these connections, and gliosis, are thought to cause the associated epileptic-seizures [4, 5, 11, 18-21]. In this case, heterotopic grey m a t t e r was found incidentally on CT. The patient had normal p s y c h o m o t o r d e v e l o p m e n t and no epileptic seizures or E E G abnormality. The r C B F of the heterotopic grey matter, and the adjacent cortex, was significantly increased by contralateral voluntary m o v e m e n t s or sensory stimulation. A reactive increase in r C B F has b e e n considered to imply neuronal activation of the corresponding area of the brain (blood flow-metabolism coupling). 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