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11 year old intact female Newfoundland with history of chronic ocular issues with strabismus and decreased retropulsion OD. Clear, viscous fluid aspirated from the mass.
A multilobular, mixed solid and loculated cavitary mass is present within the right retrobulbar space and temporomandibular region. The solid potion of the mass encompasses the right temporomandibular joint, causing osteolysis of the mandibular condyle and temporal bone at the temporomandibular joint. A cavitary portion of the mass projects caudally, extending ventral to the right horizontal auricular canal to the level of the foramen magnum. The other main cavitary portion of the mass narrows and is traced rostrally from the temporomandibular joint, bordered laterally by the right mandibular ramus, temporalis muscle and zygomatic salivary gland, and medially by the right pterygoid muscles. It displaces the salivary gland laterally, compressing it and elongating it in the dorsoventral dimension. This portion of the cavity expands rostral to the mandibular ramus, occupying the majority of right the retrobulbar space between the pterygoid muscles and right zygomatic salivary gland. The mass causes exophthalmia of the right globe, and compression and distortion of the right ophthalmic plexus and the right pterygoid and temporalis muscles. Ventromedial displacement of the right pterygopalatine fossa, and lateral displacement of the right mandibular ramus is seen. The cavity tapers at the rostral extent, projecting ventrolateral to the inferior aspect of the right globe.
In comparison to muscle, this mass is markedly hyperintense on T2•weighted images, isointense with a hyperintense rim on FLAIR images, hypointense on T1-weighted images and markedly rim-enhancing on T1 postcontrast images. At the mandibular condyle, the mass is granular in appearance on postcontrast T1-weighted images and T2 images. The regional lymph nodes are unremarkable.
Aggressive, osteolytic, right sided, temporomandibular and cavitary retrobulbar mass.
Differential diagnoses include neoplasia, such as myosarcoma or salivary gland carcinoma, or, less likely in the absence of pain, abscess with osteomyelitis/septic arthritis of the temporomandibular joint or salioadenitis with sialocele.
Myxosarcomas are mucous secreting neoplasms of connective tissue origin that are locally invasive and seem to have a predilection for the orbit. The majority are subcutaneous tumors of the trunk or limbs, but there are reports of myxosarcomas arising from the heart, eye, vertebral column and brain. When when located in the orbit, typical clinical signs include exophthalmia, periorbital swelling and pterygopalatine swelling, with or without pain on opening the mouth. MR features include solid and cystic regions with rim enhancement, and involvement of the temporomandibular joint. Osteolysis, as seen in this patient, may or may not be present. The fluid within a myxosarcoma is viscous and can appear similar to synovial fluid or that found within a mucocele. Myxosarcomas are slow growing tumors which can often be treated with periodic aspiration of the cystic contents. A year out, this patient was unchanged with no progression evident on a CT scan obtained a year after the original MR.
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