Extra-adrenal pheochromocytoma (retroperitoneal paraganglioma) in a kelpie-cross

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canine tumours
13-year-old Kelpie cross, three days post-operatively

A 13-year-old desexed male kelpie-cross underwent routine dental prophylaxis and was found to have a mass medial to both kidneys on deep palpation that was not obvious on earlier conscious examination of the abdomen. Ultrasonography revealed the presence of a large solid mass adjacent to the caudal vena cava (CVC) and the renal arteries of both kidneys. 

Prior medical history included treatment with 20mg fluoxetine SID for separation anxiety, daily meloxicam and 200mg gabapentin BID for arthritis, and Hills z/d for inflammatory bowel disease that had been present since the dog was adopted at four months of age. He had also suffered a bout of pancreatitis two years prior despite being on the aforementioned diet. He had intermittent elevations in his Spec cPL levels after this initial bout and these continued for the rest of his life.

Haematology and biochemistry were unremarkable (apart from increased cPLi from recurrent mild chronic pancreatitis). Computed tomography showed a 4.3cm x 3.7cm x 2.8cm heterogeneously contrast enhancing cavitated soft tissue mass medial to the left kidney and the CVC.

The mass effaced the left kidney and left adrenal gland, and caused focal compression/right-sided deviation of the adjacent CVC with no evidence of caval invasion. The mass involved the left renal vein, although was mostly caudal to it. The left adrenal was mildly enlarged, while the right adrenal was unremarkable. A number of contrast enhancing nodules were identified in the spleen (0.5cm-1.45cm in size), while a number of pinpoint non-contrast enhancing foci were also noted in the liver. There was no evidence of lymphadenopathy on abdominal CT, nor of thoracic metastasis. A specialist radiologist concluded that the mass was either of regional nerve plexus or adrenal origin, although a leiomyosarcoma of the renal vein could not be ruled out.

Pre-surgical biopsy or needle aspiration was not pursued due to the risk of iatrogenic rupture of the mass. Phenoxybenzamine (alpha-adrenergic blocker) 0.5mg/kg BID was started two weeks pre-operatively in case the mass was a pheochromocytoma (to minimise the risk of peri-operative hypertensive crisis, pulmonary oedema and cardiac arrhythmias), and was tapered following surgery. Pre-operative measurement of urinary catecholamines was not pursued as while this would have helped with ruling out pheochromocytoma, it would have made minimal impact on the decision to proceed with surgery.

A midline coeliotomy was performed by a specialist surgeon, and a splenectomy was performed due to the presence of multiple nodules identified on CT. Numerous small diffuse liver nodules were also biopsied, together with the pancreas.

The mass ruptured during surgery resulting in a mild amount of haemorrhage. It was removed en bloc with the left kidney and renal artery and vein, being dissected carefully off the aorta and vena cava. Gastropexy was performed prior to abdominal closure. Post-operative PCV was 40%. The patient was discharged 24hrs after surgery with no major peri- or post-operative complications. 

Histopathology showed that the retroperitoneal mass was composed of a homogenous population of small polyhedral cells arranged in packets and cords separated by congested sinusoidal blood vessels. The cells had pale eosinophilic, finely granular cytoplasm and uniform round-to-ovoid nuclei with a low mitotic index (<1 per 10 HPF). The adjacent normal autonomic nerve ganglia were visualised within surrounding adipose tissue.

canine tumours
Figure 2: Sagittal CT view with contrast enhancement with large retroperitoneal mass adjacent to descending aorta and vena cava. The mass is caudal to the left kidney. Figure 3:  Dorsal CT view with contrast enhancement with large retroperitoneal mass adjacent to the caudal vena cava and medial to both kidneys. The mass is immediately caudal to and effacing the left adrenal gland. Figure 4: Sagittal CT view with contrast enhancement with large retroperitoneal mass adjacent to the caudal vena cava, and cranially displacing, and effacing the left adrenal gland. Figure 5: Dorsal CT view with contrast enhancement with large retroperitoneal mass (green arrows) adjacent to caudal vena cava and between both kidneys. The mass is immediately caudal to the left renal vein and cranial to the left renal artery. It is partially occluding the caudal vena cava.

In sections examined, the tumour was confined within a fibrous capsule, but there were several foci of capsular infiltration suggesting malignant potential. No areas of vascular invasion or tumour embolus formation were identified, and based on the sections evaluated, the tumour appeared to have been fully resected. The adjacent left adrenal gland had adrenocortical nodular hyperplasia. Liver tissue showed evidence of vacuolar hepatopathy with occasional small subcapsular biliary cysts. Spleen tissue showed benign nodular hyperplasia.

Consultation with a specialist oncologist suggested that the patient had a guarded prognosis, and the long-term risk for metastasis was considered to be 10%. In two studies quoting dogs with retroperitoneal gangliomas or phaeochromocytomas that survive the perioperative period, most dogs died from unrelated causes with a median survival of nine months (range 1-36 months).

The option to consider treatment with toceranib (Palladia) was considered, but not pursued, in favour of monitoring of recurrence (due to complete resection of tumour, with the expected low metastatic risk). Serial monitoring of renal parameters and USG every six months did not indicate any dysfunction of the remaining kidney.

Prior to diagnosis, the patient had had symptoms of episodes of nocturnal panting and wakefulness, with worsening anxiety as well as subtle, intermittent hind limb ataxia. These were originally attributed to possible early onset canine cognitive dysfunction syndrome (CCDS) and arthritis. However, the immediate resolution of these signs post-operatively suggests that symptoms may have been due to intermittent claudication of the vena cava.

The patient remained well for three years after surgery, and was euthanased at 16 years of age due to deteriorating quality of life from progressing osteoarthritis and CCDS. This meant that he pushed the expected survival time from that expected from a range of limited reports.

The majority of the mass was caudal to the left renal vein, which is unusual for masses of adrenal gland origin, hence the uncertain classification of the mass being an extra-adrenal pheochromocytoma (as opposed to a retroperitoneal paraganglioma). The pathologist also commented that while the histological features were compatible with a neuroendocrine tumour, the lack of continuity of the mass with the medulla of the adjacent adrenal gland was not typical for pheochromocytoma (PCC). Thus the suggested diagnosis was revised to a likely retroperitoneal paraganglioma (PGL) of extra-adrenal origin.

Paragangliomas (including aortic chemodectomas) represent 0.2% of all canine tumours1, while pheochromocytomas account for <0.1%. Primary or metastatic PGLs of an extra-adrenal, retroperitoneal location are very rarely reported in dogs2.

Up to 50% of canine PCCs are incidental findings at surgery or necropsy. Clinical signs are attributed to catecholamine release in functional tumours (tachycardia, hypertension, sweating/hyperthermia, oedema, cardiac disease), but these signs are uncommon to rare in dogs. When symptoms occur, they are often intermittent, interspersed with asymptomatic periods that lasts days to years.

Most tumours are non-functional and act as a space occupying mass. Some larger tumours may cause vomiting, abdominal pain or rupture with bleeding and haemabdomen (evidence by peri-operative rupture in this case). In this patient, they may have caused claudication as neither hypertension nor tachycardia was noted on multiple examinations pre-operatively. The metastatic rate of PCCs is reported to be 13-28% in dogs, primarily involving regional lymph nodes, liver, lung, spleen, kidney and bone. Caval invasion occurs in 39-50% of canine PCC patients.

Disclosure: the patient was the author’s much-loved dog. 


References:

1. Galac S & Korpershoek E. Phaeochromocytomas and paragangliomas in humans and dogs. Veterinary and Comparative Oncol 2017; 15, 4:1158-1170

2. Ilha MR & Styer EL. Extra-adrenal retroperitoneal paraganglioma in a dog. J Vet Diagn Invest 2013; 25(6) 803-6


Dr Alex Harrison BSc. BVMS (Hons). MANZCVS (Small Animal Medicine, Small Animal Surgery)

canine tumours

Dr Alex Harrison graduated from Murdoch University in 2000 and initially worked at the Melbourne University Veterinary School. He then spent 13 years working in a busy group of veterinary hospitals in Adelaide’s south, including 10 years as a practice partner, honing his surgical skills and accepting second opinion cases from colleagues. 

Dr Harrison has completed Memberships in Small Animal Medicine and Small Animal Surgery with the Australian and New Zealand College of Veterinary Scientists. His areas of interest include oncology, advanced medical imaging and reconstructive and orthopaedic surgery.

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