More data rebutting the 2/3-2/3 rule for splenic masses

Incidence of splenic malignancy and hemangiosarcoma in dogs undergoing splenectomy surgery at a surgical specialty clinic: 182 cases (2017–2021)

Brigita Ziogaite ,Elena T. Contreras,Jason E. Horgan

Background
This study investigates the incidence and risk factors for splenic malignancy and hemangiosarcoma (HSA) in dogs undergoing splenectomy. It evaluates predictive markers for malignancy and updates diagnostic guidelines for identifying HSA in canine populations. The study aims to refine decision-making processes surrounding splenectomy, addressing the challenge of distinguishing between benign and malignant splenic lesions prior to surgery.

Methods
The retrospective analysis included 182 dogs that underwent splenectomy at a surgical specialty clinic between 2017 and 2021. Data were collected from medical records, including breed, age, sex, hematologic results, surgical findings, and histopathology reports. Multivariable logistic regression was used to identify risk factors for malignancy and HSA, examining variables such as hematocrit (HCT), platelet count (PLT), hemoperitoneum, and lesion size.

Results
Incidence: Benign lesions were the most common, diagnosed in 57.7% of cases, while malignancy (including HSA) was observed in 42.3%. HSA specifically accounted for 32.4% of cases.

Risk Factors:
-Thrombocytopenia (low PLT): Strongly associated with HSA; dogs with low PLT had 21.4 times higher odds of HSA compared to those with normal PLT.
-Anemia (low HCT): Dogs with HCT <33% were 3 times more likely to have HSA.
-Hemoperitoneum: Present in 50% of dogs; 60.4% of these had malignancy, with HSA diagnosed in 48.4%.
-Nodule Size: Smaller nodules were associated with higher malignancy risk.
-Incidental Findings: Of 33 dogs with splenic lesions found incidentally, 93.9% had benign lesions.

Survival: The survival-to-discharge rate was 91%; half of the non-surviving dogs had malignancies.

Limitations
The study's retrospective nature and reliance on medical records limit its findings. Exclusion of dogs not undergoing surgery may bias results. Additionally, histopathologic evaluations by multiple pathologists could lead to variability. Lack of long-term follow-up prevents assessment of survival outcomes.

Conclusions
The majority of splenic masses in this study were benign, challenging traditional rules like the "double two-thirds rule." Risk factors such as thrombocytopenia, anemia, and hemoperitoneum strongly predict HSA and malignancy. Careful evaluation of these markers is recommended, especially for incidental findings, where benign outcomes are likely. The findings provide critical insights to improve decision-making and communication with dog owners about splenectomy risks and benefits.