- The left kidney is effaced by a large, mostly well-defined, lobular and mixed hyper- and hypoechoic mass (yellow arrowheads) with large septated regions of anechoic fluid cavitation.
- Surrounding this mass, the retroperitoneal fat is strongly hyperechoic.
Conclusions:
- Large fluid-cavitated left renal mass with regional steatitis. Consider neoplasia primarily, such as carcinoma.
Normal left kidney ultrasound:
- The left kidney can be found between the 16th and 17th intercostal spaces and the first to third lumbar vertebrae, medial or deep to the spleen, between the level of the tuber coxae and the tuber ischii. It measures approximately 13 +/-2cm in length.
- Reference (PDF link below): Barton, Michelle Henry. “Understanding abdominal ultrasonography in horses: which way is up.” Compend. Contin. Educ. Pract. Vet 33 (2011): E1-E7.
Follow-up:
- Additional diagnostics:
- Abdominocentesis: Light yellow, slightly cloudy fluid was obtained. On cytology, probable mild neutrophilic inflammation with chronic hemorrhage was reported. No evidence of infectious agents or neoplasia were observed.
- Thoracic radiographs: No clinically significant abnormalities.
- Surgical options were discussed with the owner but due to the high risk of hemorrhage and other complications, owner elected humane euthanasia.
Necropsy:
- FINAL ANATOMIC DIAGNOSES:
- Undifferentiated sarcoma, left kidney with fibrous adhesion of the left body wall, spleen, and intestine.
- Edema, subacute, mild, locally extensive, ventral abdominal subcutaneous tissue.
- Effusion, serosanguinous, mild, acute, thoracic cavity and pericardium.
- Fibrosis, chronic, moderate, multifocal, right kidney.
- COMMENTS: There was a large (approximately 53 x 51.5 x 32 cm) abdominal mass that was adhered to the left abdominal wall, spleen, and intestine and that was arising from, and largely effacing, the left kidney. The only remnant of the kidney was an approximately 3 cm wide band of tissue markedly compressed by the mass. The mass had a bilobed appearance and on gross examination, the smaller lobe was thought to be renal parenchyma, however microscopic examination revealed that this was an extension of the neoplasm.
- On abdominal ultrasound, multiple pockets of anechoic fluid were observed, which correspond with what was seen on gross examination, as the mass contained multiple cystic structures. These cystic structures were also lined by the same spindled neoplastic cells. The cells were diffusely associated with wispy collagen fibers and a generalized myxoid background; myxosarcoma was a primary consideration, though other potential diagnoses, largely identified in human medicine and including fibromyxoid sarcomas and pleomorphic undifferentiated sarcomas, remain possible. Renal tumors in general are rare in horses and are most often of epithelial origin (carcinomas). Immunohistochemistry for various mesenchymal markers may help provide additional information regarding the cell of origin in this case.
- In addition to effacing most of the left kidney, the large mass was intertwined with the small intestine and compressed the stomach, which may have contributed to the colic signs observed clinically. The edema and effusion were likely secondary to impaired renal function and/or vascular compromise in the abdomen.
A little bit more…
- Renal neoplasia in horses is a rare but clinically significant condition, with renal cell carcinoma (RCC)—also referred to as renal adenocarcinoma—being the most commonly reported tumor type. A retrospective analysis by Wise et al. (2009) identified RCC as the predominant form of renal neoplasia in horses, accounting for the majority of 27 documented cases. These tumors are typically unilateral, locally invasive, and frequently metastatic, with common secondary sites including the lungs (59%) and liver (52%), followed by omentum, lymph nodes, spleen, and diaphragm.
Clinical Presentation and Diagnostic Challenges
- Clinical signs are often nonspecific and appear late in the disease course, contributing to poor prognosis. Common complaints include weight loss, anorexia, intermittent colic, and hematuria. Laboratory findings are generally unremarkable, though urinalysis often reveals hematuria, and peritoneal fluid may show neoplastic cells or signs of hemorrhage. Rectal palpation is a valuable tool, with 77% of cases showing abnormalities, including palpable masses or enlarged kidneys.
Ultrasonography
- Ultrasonography is the most effective imaging technique for evaluating renal architecture and identifying neoplastic lesions. Ramirez and Seahorn (1996) demonstrated the utility of transabdominal ultrasonography in diagnosing RCC in a 15-year-old mare, where a large, mixed echogenic mass replaced the caudal pole of the kidney. Ultrasound-guided biopsy confirmed the diagnosis of renal tubular cell carcinoma.
Typical ultrasonographic features of renal neoplasia include (Matthews et al. & Wise et al.):
- Mixed echogeny masses replacing normal renal architecture.
- Loss of corticomedullary distinction.
- Hyperechoic foci indicating calcification.
- Obliteration of renal anatomy in advanced cases.
Matthews et al. (1996) further emphasized that ultrasonography allows differentiation between cysts, abscesses, hematomas, and tumors. RCCs may appear as hypoechoic, hyperechoic, or complex masses, often with mineralization. Transrectal ultrasonography offers superior detail for the left kidney, especially when bowel gas obscures transabdominal views.
Biopsy and Staging
- Ultrasound-guided renal biopsy is critical for antemortem diagnosis. In Wise et al.’s study, biopsy or fine needle aspiration confirmed neoplasia in several cases, though only a few were definitively diagnosed as RCC prior to necropsy. Thoracic radiographs and abdominal ultrasound are essential for staging, given the high metastatic prevalence.
Prognosis and Treatment
- Prognosis remains poor to grave, with a median survival of 11 days post-diagnosis. Nephrectomy is the treatment of choice when the tumor is localized, but surgical success is rare due to extensive local invasion. Only one horse in the reviewed cases survived beyond discharge following nephrectomy, later succumbing to metastatic disease.
References:
- Wise, L. N., et al. “A retrospective analysis of renal carcinoma in the horse.” Journal of Veterinary Internal Medicine 23.4 (2009): 913-918.
- Ramirez, Sammy, and Thomas L. Seahorn. “Ultrasonography as an aid in the diagnosis of renal cell carcinoma in a horse.” Veterinary Radiology & Ultrasound 37.5 (1996): 383-386.
- Matthews, Hilary K., and Robert L. Toal. “A review of equine renal imaging techniques.” Veterinary Radiology & Ultrasound 37.3 (1996): 163-173.
- Penninck, D. G., et al. “Equine renal ultrasonography: normal and abnormal.” Veterinary Radiology 27.3 (1986): 81-84.
- Johns, Imogen, and Jill Bryan. “Diagnosis and staging of equine neoplasia.” Veterinary Clinics: Equine Practice 40.3 (2024): 351-369.
