Abstract

Computed tomography (CT) images of the head of a dead True's beaked whale are compared before and after decapitation. A 951 kg 455 cm adult male True's beaked whale stranded near Corolla, North Carolina, USA on 17 August 2011 during a 72 h long Atlantic Fleet Active Sonar Training (AFAST) alert. Alive when first observed at 10:10, it died spontaneously by 10:32. The animal was immediately shaded and ice blocks were placed on it by 11:30. It was loaded on an open flatbed trailer with ice at 19:30, and transported to the North Carolina State University College of Veterinary Medicine where it was placed in a 2°C walk-in cooler shortly after midnight. The morning of 18 August, the entire animal was maneuvered onto a large animal gantry for CT imaging, which commenced at 11:45. Lateral recumbency (left) maximized the penetration of the head through the scanner bore allowing imaging to just caudal of the ears. Following imaging of the head (12:12), the animal was moved to the necropsy laboratory. The head was removed from the body and returned to the CT scanner to assess the effects of decapitation, with imaging beginning at 15:20.

In CT images, there were bilateral mineral opacities in the peribullous space of the ears, a fluid meniscus in the right pterygoid sinus, and no boney changes. Prior to decapitation there were two small volumes of gas, one lateral to the right mandible condylar process, and one lateral to the right temporal bone. All other gas opacities were within expected gas-filled spaces. After decapitation, large multifocal gas accumulations were present in mandibular fat pads, blood vessels, the subarachnoid space surrounding the brain, bilaterally along the maxilla and mandibles, throughout the perilaryngeal and peripharyngeal tissues, and occasionally within the melon.

Major gross findings included multifocal necrotic regions in the cerebellum, reactive mesenteric lymph nodes, a gastro-intestinal tract devoid of ingesta, and pieces of plastic in multiple gastric chambers. Noteworthy histological findings included a granulomatous gastritis with associated degenerating parasites, and extensive cavitation of the cerebellum. The cerebellar defect was filled with abundant viable and degenerate neutrophils and eosinophils. Gitter cells were present in large numbers engulfing cellular debris. Parasitic migration in the cerebellum is considered a likely strong contributor to the encephalitis and stranding.

While some gas infiltration following decapitation is expected, the contrast between the intact and decapitated head is remarkable. Considerable effort and expense have been devoted to imaging heads that have been decapitated in air, typically towards the end of a long necropsy (or series of long necropsies), sometimes frozen, thawed, or exhumed. Such imaging can be highly informative for some purposes (e.g., evaluating boney changes, anatomical investigations), but gas artifacts obscure barotrauma assessment considerably. The extent of cranial gas infiltration observed following decapitation also warrants caution in necropsy interpretation of postcranial gas findings once blubber and vessels are severed. Imaging of fresh intact animals¹ is highly desirable for unambiguous evaluation of gas bubble formation in stranded marine mammals.

Acknowledgements

H. Broadhurst, G. Lewbart, S. O'Connell, L.S. Christian, E. F. Christiansen, S.W. Thornton, J.M. Sullivan, J. B. Minter, and M. Lustgarten all provided invaluable assistance.

Reference

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