Neuronal Migration Defect: A Case of Subcortical Heterotopia in a California Sea Lion

Abstract

A 2 and a half-year-old male California sea lion (Zalophus californianus) presented with a history of intermittent generalized seizures. Magnetic resonance imaging revealed a large focal mass occupying the right cerebral hemisphere with moderate dilatation of the contralateral lateral ventricle. At necropsy, the right cerebral hemispheric white matter was expanded by numerous irregularly shaped, pale pink nodules up to 10 mm in diameter. The overlying cortex was characterized by increased numbers of small, poorly developed gyri with shallow, often indistinct, sulci (polymicrogyria). Microscopically, nodules were composed of neurons, oligodendroglia, microglia, and supporting neuropil and were well delineated from the surrounding white matter. The gross, histological, and immunohistochemical features of this lesion are consistent with a neuronal migration defect resulting in unilateral subcortical heterotopia.

Imaging Diagnosis—magnetic Resonance Imaging of a Neuronal Heterotopia in the Brain of a Cat

“…To the authors’ knowledge this is the first report of neuronal heterotopia in a cat. It has been reported in humans, a sea lion, and as a single abstract of a Lagotto Romagnolo puppy . Neuronal heterotopia is a central nervous system malformation in which there is an arrest in the normal migration of neuronal progenitor cells from the germinal matrix into the outer layers of the developing cerebrum.…”

“…Neuronal heterotopia is a central nervous system malformation in which there is an arrest in the normal migration of neuronal progenitor cells from the germinal matrix into the outer layers of the developing cerebrum. This results in accumulations of gray matter within the cerebrum . The inciting cause of neuronal heterotopia is usually unknown (idiopathic), but potential causes include in utero infection, toxin exposure, and genetic predisposition .…”

“…It has been reported in humans, a sea lion, and as a single abstract of a Lagotto Romagnolo puppy. 2,3,[5][6][7][8] Neuronal heterotopia is a central nervous system malformation in which there is an arrest in the normal migration of neuronal progenitor cells from the germinal matrix into the outer layers of the developing cerebrum. This results in accumulations of gray matter within the cerebrum.…”

“…2,5,6,8 The inciting cause of neuronal heterotopia is usually unknown (idiopathic), but potential causes include in utero infection, toxin exposure, and genetic predisposition. 2,6 Gray matter heterotopia is relatively common in humans and is classified into three groups based on clinical and imaging characteristics: (1) subependymal, (2) subcortical, and (3) band heterotopias. 2,5 The most common type of heterotopic gray matter seen in humans is the subependymal nodular type.…”

Congenital Neuroglial Heterotopia in a Neonatal Harbor Seal (Phoca vitulina richardsi ) with Evidence of Recent Exposure to Polycyclic Aromatic Hydrocarbons

“…The only report of this lesion in the veterinary literature involves a single pharyngeal mass in a 5-wk-old domestic kitten causing displacement of the tongue without enlargement of the adjacent lymph nodes, with no recurrence after surgical resection (Cox et al, 1997). The only similar congenital lesion in a marine mammal was an intracranial subcortical heterotopia in a juvenile California sea lion (Zalophus californianus), with a mass of gray matter in the subcortical white matter of the cerebrum, presumably caused by a neuronal migration defect (Blankenship et al, 2008).…”