1. Introduction

The spleen is the largest secondary lymphoid organ and plays a central role in systemic homeostasis through its involvement in immune defense, erythropoiesis, lymphopoiesis, erythrophagocytosis, and blood cell storage. Functionally, the white pulp contributes to antibody production and immune surveillance, whereas the red pulp filters senescent or damaged erythrocytes and serves as a reservoir for erythrocytes and platelets. Due to its physiological and anatomical characteristics, the spleen is susceptible to a wide spectrum of disorders, particularly in middle‐aged and geriatric dogs [1–4].

Splenic disorders are more frequently reported in large‐breed dogs, including Golden Retrievers, Labrador Retrievers, and German Shepherds, with body weight ≥ 21 kg identified as a significant risk factor [5–10]. Clinical signs are often nonspecific and include reduced appetite, lethargy, pallor, abdominal distension or pain, weight loss, vomiting, and diarrhea [2, 11, 12]. Dogs affected by splenic tumors, whether benign or malignant, may present with hemoperitoneum and anemia secondary to splenic rupture [13, 14]. In other instances, lesions are detected incidentally during imaging or surgical procedures [9].

The so‐called “two‐thirds rule,” originally described by Johnson et al. (1989) in dogs with splenomegaly, states that approximately two‐thirds of affected dogs have neoplastic disease and that two‐thirds of these neoplasms correspond to hemangiosarcoma (HSA) [7, 15–17]. Although this concept has subsequently been widely extrapolated to dogs with splenic masses in veterinary literature [14], its predictive value appears to vary according to clinical presentation and study population. Given the overlap in clinical presentation and gross appearance between non‐neoplastic and neoplastic lesions, histopathological examination remains essential for definitive diagnosis and appropriate clinical management [18, 19].

Histopathologically, splenic lesions in dogs are broadly classified as neoplastic and non‐neoplastic. Large studies conducted in North America and Europe have reported considerable variability in their relative prevalence, which is influenced by differences in study design and inclusion criteria. In Italy, a retrospective study including 682 canine spleens with and without hemoperitoneum found that non‐neoplastic lesions predominated (54.3%), with hematoma being the most frequent (57.0%) followed by nodular lymphoid hyperplasia (NLH) (37.3%). Neoplastic lesions accounted for 45.7% of cases, with HSA being the most prevalent neoplasm (54.5%), followed by other sarcomas (19.0%) and lymphoma (15.1%) [20].

In contrast, a prospective multicenter study from the United States including 345 dogs presenting with spontaneous hemoperitoneum secondary to a ruptured splenic mass reported a lower proportion of non‐neoplastic lesions (32.75%). In that cohort, nodular hyperplasia accounted for 89.38%, followed by myelolipoma (7.96%), whereas neoplasms represented 67.25% of cases, most commonly HSA (83.6%) and other sarcomas (10.34%) [13].

In Latin America, available data are limited and heterogeneous. In Brazil, non‐neoplastic lesions have been reported in 30%–64% of cases, with higher prevalence in smaller studies and lower prevalence in larger series [1, 10, 21–25]. In Argentina, 41% of cases were classified as such, whereas in Uruguay, only nine cases were described, providing insufficient data for characterization [26, 27]. A recent large study from Chile analyzing 507 samples found a predominance of non‐neoplastic lesions (67.5%), with hyperplastic conditions being the most frequent diagnoses [28].

In Colombia, epidemiological information on splenic lesions in dogs is scarce. A small study from Caldas reported non‐neoplastic alterations in 22.7% of dogs, benign neoplasms in 59%, and malignant neoplasms in 18.1% [29]. Comprehensive data linking these lesions to systemic diseases such as infectious, degenerative, or metabolic conditions are lacking. Moreover, although diagnostic capabilities have improved nationally, the clinical relevance of splenic lesions and standardized diagnostic protocols remain poorly defined. Descriptive studies, such as the present one, provide essential baseline data to inform future research and clinical practice.

Therefore, the present study aimed to characterize the frequency and histopathological spectrum of splenic lesions in dogs evaluated through three veterinary histopathology laboratories based in Medellín between 2019 and 2024. To our knowledge, this represents the first and one of the largest laboratory‐based studies on canine splenic pathology in Colombia.