CT Findings of Feline Nasal Hamartomas Mimicking Malignant Growth.

Nasal hamartoma (NH) is a rare nonneoplastic excessive growth of native tissue of the nasal cavity. Four histological subtypes are described in cats and dogs: mesenchymal nasal hamartoma (MNH), epithelial hamartoma, mixed tissue (chondro-osseous and respiratory epithelial adenomatoid hamartoma/COREAH), and nasal vascular hamartoma. This descriptive, retrospective study aims to describe the computed tomographic (CT) features of feline NHs. Fourteen cats were included (six MNH, six COREAH, one epithelial, and one vascular). Twelve MNH and COREAH were soft-tissue and mineral-attenuating locally invasive nasal masses with expansile behavior (nine unilateral and three bilateral). The nasal turbinate architecture was replaced by exuberant/disorganized mineral densities arranged in a "cerebroid pattern" in all cases. Contrast enhancement was moderate in 75% of cats. Commonly, the mass extended into the rostral nasopharynx, contralateral choana/nasal cavity, and nostrils, more rarely into the orbital cavity and/or facial soft tissue. Focal osteolysis/atrophy of the paranasal bones was common (10/12 cases). The epithelial and vascular hamartomas were soft tissue-attenuating unilateral masses without mineral components. Contrast enhancement was marked in the vascular hamartoma. NHs are relatively rare, tumor-like growths in cats that mainly contain mesenchymal elements. Common CT features include expansile nasal lesions that are locally invasive, characterized by a mineral "cerebroid pattern." Despite the low incidence, it is crucial to be aware of their presence and include them in the differential diagnosis of feline nasal masses.