What is your diagnosis? Fine-needle aspirate from a neck lesion in a dog

An 8-year-old spayed female Labrador dog presented a bilateral, slightly asymmetric mass measuring approximately 2.5 cm in diameter in the neck. The owner noticed the lesion 10 days previously; it was sore during the physical examination. Ultrasound or computed tomography of the neck was not performed. As sialoadenitis was suspected, the dog received antibiotics for 1 week, but no clinical improvement was noticed. The diagnostic workup included a complete blood count, level of C-reactive protein, and imaging (thoracic radiography, abdominal ultrasound); no abnormalities were revealed. A fine-needle aspirate of the lesion was submitted for cytologic examination (Figure 1).

Cytologic interpretation: Malignant neoplasm with epithelioid appearance.

The aspirate of the cervical mass was similar on both sides, with moderate-to-high cellularity. The exact location of the mass was not determined. A moderate number of RBCs were present. The predominant population was atypical cells distributed in dense and loose cohesive clusters and less frequently in single cells (Figure 2). Several pseudoacinar structures were present. A small amount of pink extracellular matrix was rarely observed (Figure 3A). Cells were polygonal to infrequently spindle, with variably distinct cell borders and a moderate amount of pale basophilic cytoplasm. Small clear vacuoles were sometimes present in the cytoplasm (Figure 3). Cells with a single large cytoplasmic vacuole (signet ring-like cells) or erythrophagocytosis were rare. Nuclei measured two times the size of an erythrocyte and were oval, eccentric, or less frequently central, with finely stippled chromatin and one to four variably prominent nucleoli. Atypia was moderate: anisocytosis, anisokaryosis, and rare binucleation. Mitotic figures were not observed. The cells were admixed with occasional mast cells, plasma cells, hemosiderin-laden macrophages, and scattered neutrophils.

Excisional biopsy was performed 15 days after the first consultation. The sample, identified as a submandibular lymph node by the veterinary surgeon, was a pear-shaped nodule (2.1 cm in length; 1.5–1 cm in diameter) and was diffusely dark red on cross section. Histologic evaluation revealed an unencapsulated, infiltrative, densely cellular neoplasm, replacing almost all the preexisting lymph node. The latter was identified because of the presence of subcapsular sinuses, trabeculae lined by a well-differentiated endothelium, and rare lymphoid follicles. The sample also included a non-neoplastic lymph node adjacent to the neoplastic lesion, showing sinus erythrocytosis. Neoplastic cells were spindle to polygonal cells forming blood-filled vascular channels supported by a thin collagenous core and, to a lesser extent, solid areas (Figure 4). They had indistinct cell borders, small-to-moderate amount of eosinophilic cytoplasm, and oval nuclei with finely stippled chromatin and frequently a single prominent nucleolus. The atypia was marked with anisokaryosis, anisocytosis, karyomegaly, and binucleation. There were 11 mitotic figures in 2.37 mm². A low number of mast cells were multifocally scattered throughout the stroma. Von Willebrand factor (vWf) immunohistochemistry (polyclonal rabbit anti-human Von Willebrand Factor, clone A0082, Dako, Agilent Technologies, Santa Clara, CA, USA) was performed; neoplastic cells showed strong cytoplasmic immunoreactivity for this endothelial cell marker.

Abdominal lesion was not detected by computed tomography at the time of diagnosis. The dog was euthanized 6 months later because of local progressive disease, notably causing dysphagia. A potential spreading of the tumor over time or confirmation of the primary site could not be assessed as autopsy was not performed.

Hemangiosarcoma is a common neoplasm in dogs, likely originating from endothelial progenitor cells or hematopoietic stem cells. It generally affects middle-aged and neutered dogs, with German Shepherd Dogs, Golden Retrievers, and Labrador Retrievers being overrepresented. Our patient was an 8-year-old female neutered Labrador dog. Non-cutaneous hemangiosarcoma in the neck has been rarely reported in dogs. Chan et al. described four cases of primary cervical nodal hemangiosarcoma: all dogs had a unilateral slow-growing tumor without clinical signs at the initial evaluation.¹ This contrasts with our patient, which had a presumed bilateral tumor based on cytology and signs of pain during palpation.

Diagnosis of hemangiosarcoma on cytology might be challenging due to variable cellularity and heterogeneity of cellular morphology. In this case, several cytological features previously reported in dogs and humans were observed, namely a dual population composed of epithelioid and spindle cells, clusters of cells, cytoplasmic vacuolation, erythrophagocytosis, and mast cells admixed with the neoplastic population.^{2, 3} However, none of these findings were specific. In addition to hemangiosarcoma, erythrophagocytosis can be found in many canine tumor types, in particular hemophagocytic histiocytic sarcoma and osteosarcoma. Mast cells are frequently observed in both hemangioma and hemangiosarcoma in dogs.⁴

Vasoformative features were present and were characterized by well-formed small vessels and pseudoacinar structures. The latter could mimic an epithelial pattern. In fact, angiosarcoma misdiagnosed as carcinoma on cytology has been reported in humans and dogs.⁵ In many cases, definitive diagnosis requires at least one of the following analyses: immunocytochemistry, histology, or immunohistochemistry. In our case, the histologic appearance was typical of hemangiosarcoma, and immunohistochemistry with the endothelial marker vWf confirmed the diagnosis. This report highlights the importance of including hemangiosarcoma in the differential diagnosis of cervical nodal cytologic samples with an epithelial-like appearance.

The authors declare that they have no conflict of interest.