Phenotypic and Genomic Analysis of Cystic Hygroma in Pigs.

Cystic hygroma is a malformation of the lymphatic and vascular system and is recognized as a benign congenital tumor that affects humans and animals in the perinatal period. This congeni-tal disorder is rarely described in animals, and until today, cystic hygroma in pigs has not been described in the literature. In a purebred Piètrain litter with twelve live-born piglets, cystic hy-groma was noticed on the rump of two male pigs within the first week of life. In addition, a third case of a crossbred weaner (Large White × Landrace) was detected during a herd examina-tion. To rule out common differential diagnoses, e.g., abscess or hematoma, further clinical and pathological investigations were conducted. During clinical examination, a painless and soft mass, which was compressible, was detected on the rump of all affected animals. The ultra-sonographic examination revealed a fluid-filled and cavernous subcutaneous structure. In addi-tion, a puncture of the cyst was conducted, revealing a serosanguinous fluid with negative bacte-riological culture. In all cases, a necropsy was performed, showing that the animals had fluid-filled cysts lined by well-differentiated lymphatic endothelium. Based on the clinicopathological examination, cystic hygroma was diagnosed. Furthermore, SNP array genotyping and whole-genome sequencing was performed and provided no evidence for a chromosomal disorder. In the Piètrain family, several genome regions were homozygous in both affected piglets. None-theless, a dominant acting de novo germline variant could not be ruled out, and therefore differ-ent filtering strategies were used to find pathogenic variants. The herein presented lists of pri-vate variants after filtering against hundreds of control genomes provide no plausible candidate and no shared variants among the two sequenced cases. Therefore, further studies are needed to evaluate possible genetic etiology. In general, systematic surveillance is needed to identify ge-netic defects as early as possible and to avoid the occurrence of losses in the pig population.