Subcutaneous, abdominal, and thoracic encapsulated fat necrosis in bowhead whales Balaena mysticetus from Alaska, USA

Abstract

We describe a case series of encapsulated fat necrosis with subcutaneous, abdominal, and thoracic locations in 7 subsistence-harvested bowhead whales Balaena mysticetus. Masses had a variably-dense fibrous capsule surrounding necrotic adipocytes and calcium salts (saponification). One animal also had prior concussive injury, pleural fibrosis, and hepatic lipoma; the other animals had no significant findings. The described condition is uncommon in bowhead whales, with 7/575 (1.2%) observed from 1996 to 2015. The exact mechanisms of development of encapsulated fat necrosis in bowhead whales remain to be determined. Encapsulated fat necrosis has been reported in other baleen whales, humans, and cows. It is usually an incidental finding during post-mortem examination that needs to be differentiated from neoplastic and inflammatory lesions, as the latter may have public health implications. Assessment of further cases in bowhead whales and other baleen whales is warranted to better understand their pathogenesis.