Investigation of perioperative characteristics, treatment and outcomes of canine intrarenal cystic lesions, along with the diagnostic performance of a modified Bosniak classification for prediction of malignancy

Renal cysts (RCs) are intraparenchymal epithelium lined cavities within the renal cortex or medulla and have been infrequently reported in the veterinary literature. Several treatment options have been described including cyst fenestration (partial nephrectomy/deroofing) and omentalisation, sclerotherapy using alcohol as a sclerosing agent, percutaneous cyst drainage (PCD), and ureteronephrectomy. Information regarding presenting clinical signs, physical examination findings, and outcomes of dogs with RCs treated by different methods is limited. Furthermore, results of histopathologic analysis of treated RCs in the veterinary literature have not been routinely reported. The objective of the first study of this thesis was to provide information regarding perioperative characteristics, histologic diagnosis, complications, and outcomes of dogs undergoing treatment of intrarenal cystic lesions (ICLs). The term ICL was used instead of RC as “cyst” is specific and indicates a benign histologic diagnosis. Medical records of 11 institutions were retrospectively reviewed to identify dogs that underwent percutaneous drainage (PCD), sclerotherapy, surgical deroofing +/- omentalisation, or ureteronephrectomy for management of ICLs from 2004-2021. Six weeks postoperative/post-procedural follow-up was required. Cases suspected to represent malignancy on preoperative imaging were excluded. Eighteen dogs were included, with 24 ICLs treated. Ten had bilateral. There were 15 males and 3 females, with crossbreeds predominating. PCD, sclerotherapy, deroofing and ureteronephrectomy were performed in 5 (5 ICLs treated), 7 (11 ICLs), 6 (6 ICLs), and 7 (7 ICLs) dogs, respectively, with 5 dogs undergoing > 1 treatment. Seven dogs experienced 8 complications, with requirement for additional intervention commonest. PCD, sclerotherapy and deroofing resulted in ICL resolution in 0/5, 3/11 and 3/6 treated ICLs, respectively. Histopathology identified RCs in 7/13 dogs with histopathology available and neoplasia in 6/13 (4 malignant, 2 benign). Of 5 dogs diagnosed histopathologically with neoplasia, cytology of cystic fluid failed to identify neoplastic cells. Among 7 dogs with histologically confirmed RCs, 4 had concurrent ICLs in ipsilateral/contralateral kidney, compared with 2/6 dogs with histologically confirmed neoplasia. Human ICLs are routinely categorised according to the Bosniak classification system that allows prediction of likelihood for malignancy, in order to guide the most appropriate treatment. This classification system is mainly based on contrast enhanced computed tomography (CT) appearance of ICLs, however, adaptations of this classification system for ultrasound (US) and magnetic resonance imaging (MRI) have been described. A classification system similar to the Bosniak is lacking in veterinary medicine and could be useful to guide the most appropriate treatment in dogs with ICLs The objectives of the second study of this thesis were to propose a modification of the Bosniak classification system for US and CT that would predict the risk of malignancy in canine ICLs, assess its applicability by measuring the inter-rater and intra-rater agreement, and determine its diagnostic value by investigating its diagnostic accuracy for prediction of malignancy among imaging modalities as well as, experienced and novice radiologists. Ultrasonographic and CT images of canine ICLs with histopathologic diagnosis were reviewed by 2 radiologists in 2 separate occasions. Cases were classified according to a modified Bosniak and a dichotomous (nonsurgical versus surgical ICL) classification. Fifteen dogs were included in this study. The proposed modification of the Bosniak classification had 0.86 sensitivity, and 0.91 NPV on both US and CT, with good intra- and good to very good inter-rater agreement on US. The dichotomous classification had similar sensitivity and NPV compared to the modified Bosniak classification on both imaging modalities.