Pathologic and flow cytometric features of a case of canine ventral cervical lymphangiosarcoma

An 11-y-old spayed female German Shepherd was presented for a second opinion of ventral cervical swelling of 3-mo duration. On examination, the dog had significant dependent ventral cervical swelling. Enlarged lymph nodes with cystic changes and severe edematous facial swelling were noted on computed tomography. Fine-needle aspiration of the ventral cervical swelling revealed yellow-tinged fluid, with a predominance of lymphoid cells noted on cytologic examination. On cervical exploratory surgery, the left mandibular lymph node was surrounded by a large fluid pocket; biopsies of the lymph node were obtained. Impression smear cytology, flow cytometry, PCR for antigen receptor gene rearrangements, and histopathology were performed on samples from the left mandibular lymph node. Impression smear cytology revealed a population of atypical discrete cells. Flow cytometry identified a population of CD34+/CD45- large cells. A tumor of endothelial origin within the medulla of the lymph node was identified by histopathology, and lymphangiosarcoma was confirmed based on prospero-related homeobox gene 1 (PROX1) immunoreactivity. Our study describes the challenges in the diagnosis of a rarely reported entity and highlights that neoplastic endothelial cells should be considered as a differential when high proportions of CD34+/CD45- cells are present in flow cytometry.