Sang-June Sohn, Sohee Lim, Junghoon Park, Ulsoo Choi, Yeon-Jung Hong
Background
Paragangliomas are rare neuroendocrine tumors arising from paraganglionic tissues associated with the autonomic nervous system. While pheochromocytomas occur in the adrenal medulla, extra-adrenal paragangliomas (EAPs) are less common and often more malignant. These tumors are extremely rare in veterinary medicine, particularly in cats, with only sporadic reports in various locations such as the kidneys, heart, and retroperitoneum. The youngest previously reported feline retroperitoneal EAP cases were much older, making this report significant for extending the known age range of occurrence. Accurate diagnosis requires advanced imaging and immunohistochemistry (IHC) due to the absence of pathognomonic imaging features.
Methods (Case Description)
An 18-month-old neutered male domestic shorthair cat was referred after ultrasonography revealed a retroperitoneal mass near both adrenal glands. CT showed an irregular, mildly contrast-enhancing mass (3 × 2.5 × 3.5 cm) displacing vessels, with mild lymphadenopathy considered reactive. Fine-needle aspiration suggested a malignant round cell tumor, with differential diagnoses including lymphoma, nephroblastoma, or embryonal tumor. The mass was surgically excised, and histopathology confirmed a high-grade round cell neoplasm. IHC was performed, revealing strong positivity for neuron-specific enolase, synaptophysin, chromogranin A, and cytokeratin 19 (CK19), confirming extra-adrenal paraganglioma.
Results
This was the youngest reported feline case of retroperitoneal EAP. Imaging findings differed from previously reported cases, with the tumor showing only mild contrast enhancement and relatively uniform appearance, suggesting possible early-stage disease. IHC excluded lymphoma and nephroblastoma and confirmed paraganglioma. Notably, CK19 expression was detected for the first time in a veterinary paraganglioma, a marker associated with aggressive behavior in human neuroendocrine tumors. Postoperatively, the cat developed suspected cranial mesenteric artery thrombosis and mesenteric ischemia, leading to euthanasia on day four.
Limitations
This was a single case report with no long-term follow-up, limiting conclusions about prognosis or the clinical relevance of CK19 expression. The acute postoperative vascular event prevented assessment of recurrence or survival. Findings may not be generalizable due to the rarity of this tumor.
Conclusions
This case expands the age spectrum of feline retroperitoneal paragangliomas and highlights their potential to occur even in young cats. It demonstrates the diagnostic challenge posed by nonspecific imaging and cytology, underlining the necessity of IHC for definitive diagnosis. The novel finding of CK19 expression suggests possible prognostic value but requires further study. Despite complete surgical excision, prognosis remains guarded, emphasizing the importance of careful postoperative monitoring and long-term follow-up in similar cases.
Figure 1. Abdominal ultrasonography (A) and computed tomography (B) illustrating a hypoechoic and mild contrast-enhancing mass between both adrenal glands. A small hypodense area reflecting cystic degeneration was shown in the mass.
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