CT Clues to Canine Adrenal Tumor Survival—What Vets Need to Know

Preoperative Computed Tomography Features as Predictors of Malignancy and Survival in Canine Adrenal Tumours

William L. Snell, Ashton Cole Berger, Elisa Spoldi, Michael J. Dark, Madison Elizabeth Hurley, Monica Maria Suero, Lisa L. Farina, Carlos Henrique de Mello Souza, Judith Bertran, Elizabeth A. Maxwell

Background

Adrenalectomy in dogs presents both surgical risk and prognostic uncertainty, especially regarding tumour malignancy and survival outcomes. While CT is increasingly used for preoperative assessment, limited studies have correlated specific CT features with malignancy or survival. This study aimed to identify preoperative CT characteristics that predict malignancy and are associated with postoperative survival in dogs undergoing adrenalectomy.

Methods

This retrospective study included 201 dogs that underwent CT imaging and adrenalectomy between 2008 and 2023 at a single tertiary veterinary center. CT images were assessed by a blinded board-certified radiologist for features such as tumour size, margins, shape, mineralization, contrast enhancement, vascular invasion, and suspected metastasis. Tumour volume was scaled using vertebral body measurements and normalized to body weight. Histopathological consensus diagnosis classified tumours as benign or malignant. Survival data were analyzed using Kaplan–Meier and Cox proportional hazards models, with multivariate analysis accounting for confounders and false discovery rate correction.

Results

Out of 226 adrenal tumours, 130 were classified as malignant (mostly pheochromocytomas and adrenocortical carcinomas), and 32 as benign. Key CT predictors of malignancy included irregular margins, mineralization, and multivessel vascular invasion. However, none of these CT features were predictive of long-term survival on multivariate analysis.
Relative tumour volume >3.25 was associated with shorter survival on univariate analysis and remained significant on multivariate analysis when all deaths were included (p = 0.0008).
Vascular invasion, especially in left-sided tumours, significantly impacted survival (e.g., invasion of the phrenicoabdominal vein and renal vein led to MSTs of ~270–315 days vs. >1000 days for non-invasive tumours).
Bilateral adrenalectomy resulted in shorter MST compared to unilateral surgery (623 vs. 697 days; p = 0.02), though this difference diminished when perioperative deaths were excluded.
Additional surgeries such as splenectomy and ureteronephrectomy were associated with significantly reduced survival, with ureteronephrectomy retained as a predictor on multivariate analysis.

Limitations

Retrospective design introduces potential biases, including variability in CT protocols and lack of necropsy confirmation for metastasis or cause of death. Some CT-detected vascular invasions may have been underestimated due to tumour size or imaging limitations. Additionally, histopathologic classification may not reflect tumour biological behavior, as malignancy assignment did not correlate with survival.

Conclusions

While certain CT features (e.g., irregular margins, mineralization, multivessel invasion) are associated with malignancy, only relative tumour volume predicted survival on multivariate analysis. Malignancy status itself did not correlate with long-term outcome. Factors such as age, concurrent splenectomy, and ureteronephrectomy were more strongly predictive of shorter survival. CT remains useful for surgical planning and assessing risk, though its utility as a sole prognostic tool is limited.

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