1-year-old female spayed Lhasa Apso

• There is a diffuse absence of cerebral sulci and gyri with a smooth cerebral surface on all sequences. The corona radiata is not visualized. The rostral aspect of the corpus callosum is absent and the caudal aspect is thin, best seen on the transverse T2-w images. There is moderate to marked enlargement of both lateral ventricles with an absent septum pellucidum. There is a 7 mm by 9.5 mm by 11.5 mm supracollicular fluid accumulation due to dorsocaudal expansion of the third ventricle. No abnormal contrast enhancement is detected.

Lissencephaly with concurrent internal hydrocephalus, absent septum pellucidum, supracollicular fluid accumulation, and corpus callosum hypogenesis.

• The patient was continued on Phenobarbital and was started on an additional anticonvulsant (Zonisamide).
• A week later the patient was euthanized for acute worsening of neurologic signs.
• A necropsy was not performed.

Case discussion

Lissencephaly is a rare malformation of the brain presumed to be the result of incomplete migration of immature neurons to the cortical plate during fetal development1. It is characterized by a decrease or lack of gyral formation (pachygyria or agyria) and a thickening of the cerebral cortex. While the cortical changes are the hallmark of the disease, additional brain abnormalities such as dilation of the lateral ventricles and hypogenesis of the corpus callosum or cerebellar vermis can also be seen1. Lissencephaly is considered the most severe type of neuronal migration disorder compatible with life1. In humans, lissencephaly has been subdivided into two types. Type I (classical) lissencephaly is characterized by an abnormally smooth, thick cortex while Type II lissencephaly (cobblestone cortical malformation) presents a nodular cortical surface2. In veterinary medicine the reported cases in dogs are most consistent with human Type I lissencephaly1. Lhasa Apso dogs are overrepresented3. Lissencephaly has also been reported in the Australian Kelpie, Irish Setter, Pekingese, Shih Tzu, Wire Haired Fox Terrier, and a mixed breed dog3. Clinical signs associated with lissencephaly include early onset seizures, behavioral abnormalities, and visual deficits1. Concurrent corpus callosum abnormalities may cause hypodipsia/adipsia, tremors, and seizures4. Magnetic resonance imaging is the best modality for evaluation of lissencephaly due to its ability to delineate the sulci, gyri, and gray/white matter. MRI findings include thickened cerebral gray matter with broad and flat gyri, absence of major sulci, and a thin internal capsule with a lack of the corona radiata1. Additional findings reported in dogs include lateral ventriculomegaly/internal hydrocephalus, supracollicular fluid accumulation, and corpus callosum hypoplasia3.

References 

1. Saito M, Sharp NJ, Kortz GD, et al. Magnetic resonance imaging features of lissencephaly in 2 Lhasa Apsos. Vet Radiol Ultrasound. 2002;43(4):331-337. doi:10.1111/j.1740-8261.2002.tb01013.x

2. Fry AE, Cushion TD, Pilz DT. The genetics of lissencephaly. Am J Med Genet Part C Semin Med Genet 2014;166C: 198– 210.

3. Rodríguez-Sánchez DN, Pinto GBA, Thomé EF, Machado VMV, Amorim RM. Lissencephaly in Shih Tzu dogs. Acta Vet Scand. 2020;62(1):32. doi:10.1186/s13028-020-00528-0

4. Gonçalves R, Volk H, Smith PM, et al. Corpus callosal abnormalities in dogs. J Vet Intern Med. 2014;28(4):1275-1279. doi:10.1111/jvim.12371