Shoko Fukuda 1, Tetsuya Kobayashi, Ian D Robertson, Fukiko Oshima, Eri Fukazawa, Yuko Nakano, Shin Ono, Donald E Thrall

Background
Hemangiosarcoma (HSA) is a common malignant vascular tumor in dogs, often involving visceral organs such as the spleen, liver, and heart. Accurate antemortem diagnosis is critical but challenging, particularly when tumors are located in atypical sites or lack pathognomonic imaging features. This study aimed to characterize the computed tomographic (CT) features of confirmed and presumed noncutaneous HSA in dogs, evaluating associations with histopathological confirmation and anatomical distribution.

Methods
This retrospective, multicenter study reviewed CT images and medical records from 131 dogs with suspected noncutaneous HSA, including 87 with histopathological confirmation and 44 presumed based on clinical and imaging findings. CT features assessed included lesion number, location, size, enhancement pattern, margins, and presence of hemorrhage or cavitation. Statistical analysis compared CT characteristics between confirmed and presumed cases and among anatomical sites.

Results
The spleen was the most common primary site, followed by the liver and right atrium. CT findings included large, cavitated, heterogeneously enhancing masses, often with associated hemorrhage or hemoabdomen. Histopathologically confirmed cases more frequently showed multiple lesions and involvement of more than one organ. CT features were not specific enough to distinguish HSA from other neoplasms or benign lesions, although right atrial masses with concurrent pericardial effusion and splenic masses with hemoabdomen were highly suggestive of HSA.

Limitations
The retrospective design and inclusion of presumed cases without histological confirmation limit the strength of associations. Variation in CT protocols and imaging quality across centers may have introduced inconsistencies. The study's findings are primarily descriptive and may not generalize to all clinical settings.

Conclusions
Noncutaneous HSA in dogs presents on CT with characteristic but not pathognomonic features, typically as large, cavitated, heterogeneously enhancing masses. While CT is useful in identifying and staging lesions, definitive diagnosis requires histopathology. Awareness of common imaging patterns can improve clinical suspicion and guide diagnostic and therapeutic decisions. Further prospective studies are needed to refine imaging criteria for HSA diagnosis.

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