Distribution of leptomeningeal glioneuronal heterotopia in alobar holoprosencephaly

Neuropathology of holoprosencephaly

Holoprosencephaly (HPE) is a brain malformation which results from a primary defect in induction and patterning of the rostral neural tube during early embryogenesis and usually considered as an impaired cleavage of the prosencephalon. The review of neuropathologic findings highlights a complex malformation involving not only the prosencephalon but also the whole brain, the eyes, and the cerebral vascularization. The classical form of HPE is divided in three sub-types according to DeMyer classification, although the spectrum is far wider, ranging from the most severe, aprosencephaly/atelencephaly, to milder forms such as syntelencephaly and to the less severe ends of the spectrum. Macroscopy and microscopy abnormality patterns are described extensively, allowing a comparison of the anatomic features between each form. Disturbances observed in the main cerebral structures including the basal ganglia, the commissures, the hippocampus, the brainstem, the cerebellum, and spinal cord are reviewed. Macroscopic and microscopic features of the ophthalmic anomalies are described, as well as brain vascular and associated central nervous system malformations.

Anterior cranial base glioneuronal heterotopia

BACKGROUND

Cranial base glioneuronal heterotopia is a nest or linear array of glioneuronal tissue within the basal meninges. It is thought to arise from aberrant migration of embryonic neuroepithelial tissues into the subarachnoid space. It frequently mimics tumors and may extend through basal skull bones into extracranial soft tissues.

CASE REPORT

We describe a case of intracranial anterior skull base leptomeningeal glioneuronal heterotopia in a newborn female who was diagnosed in the prenatal period by ultrasound examination to have an intracranial space-occupying lesion at 35 weeks of gestation. There was no evidence of increased intracranial pressure at birth. Magnetic resonance imaging showed a large, predominantly solid, minimally enhancing tumor in the anterior cranial fossa extending into the suprasellar region as well as into the right and left middle fossae. The gross tumor was totally resected through bifrontal craniotomy.

CONCLUSIONS

Although uncommon, diagnosis of intracranial extracerebral glioneuronal heterotopia should be strongly ascertained while evaluating intracranial space-occupying lesions during the prenatal period and infancy. It needs to be distinguished histologically from teratoma and primary central nervous system tumors. Prenatal screening for early diagnosis of the lesion is vital. The location of the lesion and its relationship to the surrounding structures should lead to an accurate diagnosis in the majority of cases. Complete resection is curative and should be the goal. Long-term prognosis is excellent in view of the benign nature and extraaxial origin of the lesion.

Aberrant neuronal migration in the brainstem of fukuyama-type congenital muscular dystrophy

We examined the brainstem of 10 patients with Fukuyama-type congenital muscular dystrophy (FCMD). In the midbrain we noted leptomeningeal glioneuronal heterotopia (LGH) (n = 9) and intramural "micropolygyria" (n = 1) in the tectum, as well as tyrosine hydroxylase-positive ectopic neurons/fibers ventral to the cerebral peduncle (n = 3). In the pontomedullary region, glial fibrillary acidic protein-positive subpial tissue intermingled with neurons and myelinated fibers was present in the ventrolateral pontine surface in all cases and extended over the lateral surface of the upper medulla oblongata. This subpial gliotic band was often contiguous with the extra-pial LGH tissues. The gliotic band protruded from the ventrolateral pontine surface in 3 cases and appeared to include ectopic neurons of the pontine nucleus. Disarrangement of the arcuate nuclei (n = 3) was also noted in the medulla oblongata. We hypothesize that both the radial and tangential neuronal migration systems are disrupted in the FCMD brainstem in addition to altered neuronal migration in the cerebral and cerebellar cortex. Fukutin protein may play a part in the morphogenesis of certain neuronal structures in the brainstem and the dysplastic structure termed "aberrant pyramidal tract" in previous reports may essentially result from an ectopic migration of pontine nucleus neurons.

Molecular pathology of human cerebral malformations

Molecular pathogenesis of human cerebral malformations is briefly reviewed from a neuropathologic viewpoint, with emphasis on holoprosencephaly and neuronal migration disorders. Immunopathologic approaches are useful in elucidating the essential pathomechanism of these anomalies. In alobar holoprosencephaly, for instance, immunostaining for glial fibrillary acidic protein clarifies the pathologic significance of the leptomeningeal glioneuronal heterotopia along the ventral prosencephalic surface. In type 1 lissencephaly and subcortical laminar heterotopia, immunohistochemistry for the causative gene products revealed the temporal and spatial pattern of their localization in the normally developing cerebrum, as well as their reduction in these disorders.

Experimentally induced leptomeningeal glioneuronal heterotopia and underlying cortical dysplasia of the lateral limbic area in rats treated transplacentally with methylmercury

Leptomeningeal glioneuronal heterotopia (LGH) is a developmental anomaly sometimes observed at the surface of human brains with severe malformations. We experimentally induced LGH in brains of rat pups by transplacental exposure to methylmercury. Histopathological profiles of the induced LGH, including the spatio-temporal predominance of the manifestation, suggest some aspects of the histogenesis of this malformation. Pregnant rats on embryonic day 8 (E8), E11, E13, E16, E18 or E21 were treated orally with a single administration of 20 mg/kg methylmercury chloride, and the brains of their delivered offspring were examined on postnatal day 7 (P7) and P28. The incidence of LOH varied significantly according to the treatment day: it was almost exclusively restricted to individuals treated on E13. Furthermore, all the induced LGH was confined to the subarachnoid space dorsal to the rhinal fissure, unilaterally or bilaterally. A part of the nest was connected to the underlying cortical surface of the lateral limbic area, where glia limitans and basal lamina were disrupted. Narrow stripes of disarrangement of cortical neurons underlying the bridges were observed. The P7 LGHs consisted mainly of neurons, some of which were GABA-immunolabeled. and a small number of astrocytes as well as endogenous blood vessels and fibroblasts. LGHs in P28 brains consisted mainly of GFAP-positive astrocyte processes. An additional experiment with double administrations of 5-bromo-2-deoxyuridine (BrdU) and methylmercury on E13 disclosed an abnormally widespread distribution of labeled neurons throughout all cortical layers underlying the LGH in P28 brains. Thus, cerebral LGH would be induced if a developing brain were insulted at the early stage of neurogenesis. accompanied by cortical dysplasia.

Fluorescence in-situ hybridisation and molecular studies used in the characterisation of a Robertsonian translocation (13q15q) in Prader-Willi syndrome

A patient with classical Prader-Willi syndrome was found to have a Robertsonian translocation 45,XY,t(13q15q)mat. On CBG banding, the translocation chromosome had a large centromere with one primary constriction. Using fluorescence in situ hybridisation, positive signals were obtained with chromosome 13 and chromosome 15 centromere probes, proving that the translocation was dicentric. NOR banding was negative in this chromosome, suggesting that the breakpoints were at 13p11 and 15p11. DNA studies showed that, while there was no deletion involving 15(q11-13), maternal uniparental disomy for chromosome 15 was present. We compare our findings with the five other cases of familial Robertsonian translocation PWS that have been reported.