Abstract
A 3-week-old, stranded male Atlantic harbor seal (Phoca vitulina concolor) presented with cerebellar ataxia, delayed postural reactions, hyperesthesia, and nystagmus. The seal’s skull was enlarged and domed in shape. Ultrasound through a persistent fontanelle in the frontal bone revealed hydrocephalus. Magnetic resonance imaging (MRI) showed diffuse enlargement of the ventricular system, an absent cerebellar vermis, and hypertrophy of the choroid plexus of the fourth ventricle. Throughout rehabilitation, the seal failed to achieve milestones critical for successful release or placement in a managed care facility, including the ability to feed independently and haul out. The seal was euthanized due to poor prognosis. Postmortem gross and microscopic examinations of the encephalon confirmed a) aplasia of the dorsal cerebellar vermis and hypoplasia of the dorsal cerebellar hemispheres; b) severe, diffuse, congenital communicating hydrocephalus; and c) aplasia of the interthalamic adhesion and corpus callosum. These abnormalities were consistent with Dandy-Walker-like malformation (DWLM) as described in humans. DWLM is a rare condition in veterinary species and has been reported in cows, horses, sheep, dogs, and a cat.5,8 Alteration in the low-density lipoprotein receptor gene has been identified as a causative agent of DWLM in dogs.2,4 Congenital malformations are uncommonly reported in marine mammals, with limited understanding of the anatomical development from fetus to mature adult.3,7 This case represents the first case of DWLM in a marine mammal and illustrates the importance of advanced imaging and postmortem examination in free-ranging pinnipeds that strand with evidence of neurologic disease.
Acknowledgements
The authors wish to thank the staff and volunteers at the Mystic Aquarium Animal Rescue Program for their invaluable contributions to this case and their efforts in pinniped rehabilitation and conservation. In addition, the authors wish to thank the staff at Pieper Veterinary for their assistance with the diagnostic imaging in this case.
*Presenting author
+Student presenter
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