Epidemiology and Survival of Dogs Diagnosed with Splenic Lymphoid Hyperplasia, Complex Hyperplasia, Stromal Sarcoma and Histiocytic Sarcoma

SIMPLE SUMMARY: Dogs are frequently diagnosed with nodular lesions affecting the spleen. One of the most common lesions has been traditionally classified as fibrohistiocytic nodules but has more recently been separated into different types: lymphoid hyperplasia, complex hyperplasia, stromal sarcoma, and histiocytic sarcoma. Notably, there are contradictory reports on the survival times of dogs diagnosed with stromal sarcoma and histiocytic sarcoma. In addition, some studies have found an association between the diagnosis of these nodules with the dog’s age, breed, sex, and survival time. This paper aims to estimate the frequency of the previously known fibrohistiocytic nodules among splenectomized dogs and identify associations between the four different types of nodules with the age, sex, breed, and survival. Typical survival times varied markedly between the four types of nodules. These findings reveal widely different outcomes for dogs diagnosed with each fibrohistiocytic nodule, providing useful information to clinicians on the survival estimates of these lesions. ABSTRACT: Canine splenic fibrohistiocytic nodules traditionally encompassed benign lymphoid hyperplasia, complex hyperplasia, and malignant fibrous histiocytoma. The latter has been recently re-classified into histiocytic sarcoma and stromal sarcoma. Reliable indicators of post-splenectomy survival and demographic factors predisposing to the four types of nodules are not completely understood. This study aims to estimate frequency, survival times, and identify risk factors of splenectomized dogs diagnosed with lymphoid hyperplasia, complex hyperplasia, histiocytic sarcoma, and stromal sarcoma using medical records containing histopathological diagnosis from the VetCompass Australia database (1989–2018), which collects demographic, and clinical information from veterinary clinics. Out of 693 dogs, 315 were diagnosed with fibrohistiocytic nodules, mostly lymphoid hyperplasia (169/693, 24.4%), followed by stromal sarcoma (59/693, 8.5%), complex hyperplasia (55/693, 7.9%), and histiocytic sarcoma (32/693, 4.6%). Dogs aged 8–10 years were more likely to be diagnosed with histiocytic or stromal sarcoma than lymphoid hyperplasia. Dogs diagnosed with lymphoid hyperplasia had a longer survival time than those with other diagnoses (median > 2 years). Dogs diagnosed with histiocytic sarcoma had longer survival times (median 349 days) than stromal sarcoma (median 166 days). Results suggest that knowledge of the type of splenic fibrohistiocytic nodule, patients’ age, and sex can be used to increase prognostic accuracy.