Peripheral Nerve Sheath Tumor in the Upper Eyelid in a Dog

Background: Schwannomas are benign neurogenic tumours of peripheral nerves. They originate from Schwann cells, which form the neural sheath.Peripheral nerve sheath tumors are most commonly found on the head and neck regions of both dogs and people. Schwannomas are rarely observed in ophthalmic areas. When they occur, ocular Schwannomas are usually located in the orbit, uveal tract and conjunctiva. The occurrence of uveal schwannoma, a subset of PNST has been well documented in the veterinary literature. This is the first report of a palpebral PNST in the dog. The lip-to-lid flap is a feasible technique to reconstruct the upper eyelid following wide surgical removal of a tumor in the dog.Case: A 9-year-old, spayed female mixed-breed dog was referred for evaluation of a large mass involving the right upper eyelid for a duration of approximately one month. The inspection revealed sero-sanguinolent discharge and an oval-shaped mass occupying more than 70% of the right upper eyelid. The dog was alert and the ophthalmic and general physical examination did not revealed abnormalities. Ocular ultrasonography did not show significant findings. A fine-needle aspirate of the palpebral tumor was not elucidative, even so, a presumptive diagnosis of eyelid neoplasia was considered most likely. Excision of the entire mass with a 2 cm margin was performed. The third eyelid and dorso-medial bulbar conjunctiva were also removed. Upper eyelid reconstruction was performed based on a similar technique previously described in cats (lip-to-lid flap). As a result, neoplastic spindle cells exhibited immunoreactivity for S100 and intense cytoplasmic staining for vimentin, supporting the diagnosis of schwannoma. Fifteen days later, the margins of the subdermal pattern flap were healed and skin sutures were removed. On the last follow-up, 9 months post-surgery, the dog was visual, and the flap was well incorporated and covered the ocular surface. Ten months later, another large mass arising from the right inferior palpebral conjunctiva was observed. Once ultrasound revealed orbital invasion exenteration combined with orbitectomy were performed, and the defect was covered with an auricular axial pattern flap. Although the second tumor had the same histological and immunohistochemical characteristics of the first mass additional staining for Ki67 was used to investigate the biological behavior of both masses.Discussion: Reported eyelid neoplasms in dogs include adenomas and adenocarcin