An 8.5-year-old, female spayed Australian Shepherd initially presented with an acute history of left facial and periocular swelling. An intraoral examination under general anesthesia revealed bruising of the ipsilateral oropharyngeal wall, but no obvious cause for this bruising. A fine-needle aspirate of the swelling was performed, but the cytologic results were inconclusive. The swelling initially resolved following treatment with meloxicam.
Six weeks following her initial presentation, the dog presented with left exophthalmos and decreased range of motion in her jaw, especially opening when yawning. On physical examination, she had left exophthalmos with a dorsolateral deviation of the globe (Figure 1), inability to retropulse the globe, and moderate conjunctivitis and epiphora. She had no evidence of oropharyngeal bruising, but there was pain on opening her jaw. A retrobulbar mass or abscess were the two most likely causes of her clinical presentation.
Figure 1. Exophthalmos with a dorsolateral deviation of the globe as a result of a retrobulbar mass.
Pre- and post-contrast computed tomography (CT) scans of her head and neck were performed in addition to a thoracic CT scan. This showed a contrast-enhancing 3.0cm x 3.7cm x 4.2cm retrobulbar mass involving the left temporalis muscle and between the vertical ramus of the mandible and orbital bone, but with no bone involvement (Figure 1). There was no evidence of lymphadenomegaly or pulmonary metastasis. A fine-needle aspirate of the mass was performed with a cytologic diagnosis of a sarcoma.
Figure 2. A contrast-enhancing mass in the caudal retrobulbar space arising from the temporalis muscle.
The owners elected to proceed with surgery. A lateral approach was made to the left orbit. The temporalis and masseter muscles were incised and elevated off the dorsal and ventral aspects of the zygomatic arch, respectively. Rostral and caudal osteotomies of the zygomatic arch were performed with an oscillating saw (and the resected zygomatic arch was preserved in saline) (Figure 3) to expose the rostral aspect of the retrobulbar mass and the vertical ramus of the mandible.
Figure 3a (left). An osteotomy of the rostral zygomatic arch is being performed with an oscillating saw. Figure 3b (right). The zygomatic arch has been resected following rostral and caudal osteotomies. Removal of the zygomatic arch permitted exposure to the rostral aspect of the retrobulbar mass and the vertical ramus of the mandible.
The masseter muscle was transected along the lateral aspect of the vertical ramus of the mandible dorsal to the temporomandibular joint. The vertical ramus was osteotomized at this level with an oscillating saw, preserving the temporomandibular joint to expose the caudal aspect of the retrobulabr mass (Figure 4).
Figure 4a (left). The masseter muscle has been transected to expose the vertical ramus of the mandible (arrow). Figure 4b (right). An osteotomy of the vertical ramus of the mandible is being performed with an oscillating saw to expose the caudal aspect of the retrobulbar mass.
The masseter and temporal muscles were transected with a LigaSure for medial, dorsal, and lateral margins. The tumor abutted the caudal aspect of the globe, hence an enucleation was performed en bloc with the retrobular mass excision (Figure 5). The zygomatic arch was replaced and fixed in position with a 6-hole 2.0mm dynamic compression plate rostrally and a 5-hole 2.0mm dynamic compression plate caudally to maintain facial features as normally as possible (Figures 6 and 7). The surgical site was lavaged with sterile isotonic saline and the defect was closed routinely in two layers. The dog recovered uneventfully from surgery. The histopathologic diagnosis was a completely excised, grade III retrobulbar hemangiosarcoma.
Figure 5a (left). The rostral aspect of the retrobulbar mass (arrow) was abutting the caudal aspect of the globe. As a result, an enucleation was performed to achieve wide excision of the mass (Figure 5b, right).
Figure 6a (left – intraoperative) and 6b (right – postoperative radiograph). The zygomatic arch has been replaced and fixed in position with 2.0mm dynamic compression plates rostrally and caudally to maintain facial cosmetics.
Hemangiosarcoma is a common tumor in dogs but is more common in locations such as the spleen, liver, and heart. Cutaneous hemangiosarcoma has a less aggressive biologic behaviour than visceral hemangiosarcoma; but the reported metastatic rate for subcutaneous and muscle hemangiosarcoma is 42%-73%. In one study, the median survival time of dogs with subcutaneous and muscle hemangiosarcoma was significantly better if the hemangsarcoma was completely excised (399 days) compared to incomplete excision (89 days with residual macroscopic disease). Other prognostic factors include tumor size (with median survival times of 364 days for tumors < 4cm, 212 days for tumors 4cm-6cm, and 130 days for tumors > 6cm, respectively) and the presence of metastatic disease at the time of diagnosis (median survival time 115 days). There is minimal published information on the prognosis for dogs with muscle hemangiosarcoma treated with surgery and chemotherapy, but dogs with subcutaneous hemangiosarcoma have a significantly improved survival time with the addition of chemotherapy compared to surgery alone (median survival times of 246-399 days with surgery alone versus 1189 days with surgery and doxorubicin). Chemotherapy has been recommended for this dog and the owners are considering this option.
Figure 7. Appearance of the dog approximately 4 hours following surgery.
ACVS Founding Fellow in Surgical Oncology
VCA Canada-Alta Vista Animal Hospital, Ottawa, Ontario, Canada