4. Discussion

Splenic disorders in dogs encompass a wide spectrum of lesions with diverse etiologies and biological behaviors [2, 15, 18]. The increasing detection of these conditions is likely related to the widespread use of advanced diagnostic imaging techniques, particularly ultrasonography [32, 33], together with cytological [3, 34, 35] and histopathological evaluation. In the present study, a large retrospective histopathological evaluation of splenectomized dogs was performed to better characterize the epidemiological and pathological patterns of splenic disease in a regional population.

Three principal findings emerged from this study. First, non‐neoplastic lesions were more frequent than neoplastic processes in dogs undergoing splenectomy. Second, splenitis represented an unexpectedly high proportion of non‐neoplastic diagnoses. Third, multiple concurrent histopathological diagnoses were frequently identified within the same spleen, highlighting the complex pathological processes that may occur simultaneously in this organ.

The relative proportion of neoplastic and non‐neoplastic splenic lesions has been widely discussed in veterinary literature and is often summarized by the so‐called “two‐thirds rule,” originally described in dogs with splenic enlargement in a mixed surgical and postmortem population [7]. Although this concept has subsequently been broadly applied to dogs with splenic masses, later studies have shown that its predictive value varies considerably according to case selection, clinical presentation, and inclusion criteria.

In dogs presenting with hemoperitoneum secondary to splenic mass rupture, neoplasia has been reported in 67.2% (232/345) of cases, of which 83.6% (194/232) were HSA [13]. Similarly, another large retrospective study reported HSA in 87.3% (733/840) of malignant splenic lesions, although this proportion may be overestimated because benign neoplasms were not included in that analysis [36]. In contrast, studies evaluating incidentally detected nonruptured splenic nodules/masses or splenomegaly have reported a substantially lower proportion of neoplastic disease, with neoplasia accounting for 32.4% (34/105) and 44.8% (87/194) of cases, respectively. In those studies, HSA represented 52.9% (18/34) and 50.6% (44/87) of neoplasms [9, 37].

In the present study, neoplastic lesions represented 33.5% (142/424) of cases, which is considerably lower than proportions reported in studies focusing exclusively on ruptured splenic masses. This difference is likely explained by the heterogeneous nature of our study population, which included dogs with a variety of clinical and macroscopic presentations. Therefore, direct comparisons with studies restricted to dogs with hemoperitoneum should be interpreted cautiously.

Among neoplastic processes, HSA was the most frequent diagnosis, representing 63.4% (90/142), consistent with previous reports identifying HSA as the most common splenic neoplasia in dogs [5, 38–42]. The reported prevalence of HSA varies widely across studies (46%–92%) [5, 36, 38, 43–46], likely reflecting differences in study populations, particularly the inclusion of dogs presenting with ruptured tumors or hemoabdomen.

In the present study, 59.3% (32/54) of dogs with hemoabdomen were diagnosed with HSA, and a strong association between these variables was identified, supporting previous observations that this neoplasm is particularly prone to rupture and bleed prior to diagnosis [9, 42, 47]. However, a substantial proportion of dogs with HSA in the present cohort did not present with hemoabdomen at diagnosis, and several cases were identified incidentally during ultrasonographic evaluation or presented only with abdominal signs. These findings highlight that, although abdominal bleeding should raise strong clinical suspicion for splenic HSA, its absence does not exclude this diagnosis.

In addition to the association between HSA and hemoabdomen, several statistically significant relationships identified in this study further support the complex clinicopathological presentation of splenic disease in dogs, particularly the association between incidental detection and non‐neoplastic diagnoses, as well as the frequent coexistence of multiple lesions within the same spleen.

Hemorrhagic splenic lesions represent an important diagnostic challenge in veterinary pathology. Previous studies have emphasized the frequent coexistence of splenic hematoma and HSA, noting that hemorrhagic lesions may partially or completely obscure underlying malignant vascular tumors [2, 18, 31, 39]. In such cases, incomplete sampling or limited histological evaluation may lead to underdiagnosis of HSA. These findings support current recommendations advocating extensive sampling of hemorrhagic splenic masses and, when indicated, the use of immunohistochemistry to improve diagnostic accuracy.

Interestingly, no significant association between splenic hematoma and HSA was identified in the present study. This finding likely reflects the high proportion of primary hematomas within the cohort that were not associated with underlying neoplasia, which may dilute the apparent relationship between hematoma formation and malignancy. Therefore, although hematomas may coexist with splenic neoplasia, their presence alone should not be considered a reliable predictor of HSA.

One of the most notable findings of this study was the high prevalence of splenitis, which represented 54.6% (154/282) of non‐neoplastic cases. This proportion greatly exceeds those reported in previous studies, where inflammatory splenic lesions typically represent less than 8% of diagnoses [1, 7, 8, 37, 48]. Several factors may explain this discrepancy.

First, regional epidemiological factors may contribute to increased stimulation of the spleen. Dogs in Colombia are frequently exposed to a variety of vector‐borne and infectious agents, including Ehrlichia, Anaplasma, and Leishmania, with reported seroprevalence rates exceeding 30%–70% in some regions [49]. Although special stains or ancillary tests were not performed to identify infectious agents in the present study, chronic antigenic stimulation associated with these pathogens could contribute to reactive splenitis.

Second, methodological and diagnostic differences may have influenced the recorded prevalence. In the present cohort, splenitis was documented whenever histological evidence of inflammation was identified, even when other lesions were present concurrently. In addition, hemorrhagic splenitis represented the most frequent inflammatory pattern (46.8%, 72/154). In some diagnostic settings, similar lesions might instead be interpreted as secondary hemorrhage rather than primary inflammatory disease, reflecting the absence of universally accepted histopathological criteria for distinguishing these processes. Consequently, interobserver variability among pathologists may partially explain differences between studies. These findings highlight the importance of interpreting splenic lesions within their broader clinical and epidemiological context, as multiple pathological processes may coexist and influence the final histopathological diagnosis.

Another important observation was the frequent occurrence of concurrent histopathological diagnoses within the same spleen. Unlike many neoplastic diseases that tend to present as single dominant lesions, non‐neoplastic splenic cases often represent overlapping or sequential pathological processes. This complexity highlights an important diagnostic consideration: Evaluation of limited tissue samples may fail to detect clinically relevant lesions present elsewhere in the organ. For this reason, systematic histological examination of multiple sections from different regions of the organ is recommended to improve diagnostic accuracy.

The relatively high proportion of incidentally detected splenic lesions in this cohort also raises important clinical considerations. Approximately one‐third of the cases were discovered incidentally (143/424), and the majority of these lesions were non‐neoplastic (74.8%, 107/143). Similar findings have been reported in studies evaluating incidentally detected splenic lesions, where benign diagnoses represented most cases [9, 14]. These results suggest that not all splenic lesions detected during imaging necessarily require immediate splenectomy, and careful clinical evaluation is warranted to balance the potential benefits and risks of surgical intervention. Future studies comparing clinical outcomes between surgically and conservatively managed dogs with incidental splenic findings would be valuable.

Finally, several limitations should be acknowledged. The retrospective design and reliance on submission form data may have introduced selection and information biases. In addition, cases were obtained from three referral histopathology laboratories rather than from a population‐based cancer registry; therefore, the findings should not be interpreted as incidence estimates for the general canine population in Colombia. Differences in referral patterns, case submission, and completeness of clinical records among centers may also have influenced the study population. Histopathological evaluation was based on submitted tissue samples rather than standardized whole‐organ protocols in all cases, potentially affecting lesion detection. Furthermore, immunohistochemistry was not routinely available, which may have limited the precise classification of some mesenchymal tumors, particularly when differentiating solid HSA from undifferentiated or stromal sarcomas.