JAVMA, Vol 221, No. 11, December 1, 2002 Vet Med Today: What Is Your Diagnosis? 1553

What Is Your Diagnosis?

HistoryA 10-year-old castrated male Springer Spaniel was evaluated because of a 2- to 3-month history of a prolapsed

and swollen nictitating membrane of the right eye that was initially responsive to treatment with orally adminis-tered antimicrobials and corticosteroids. Physical examination findings were unremarkable. Results of CBC andserum biochemical analyses were within reference ranges. Ophthalmic examination revealed that the right eye hadvision with a normal pupillary light reflex, and intraocular pressure of 12 mm Hg. The right eye was difficult toretropulse digitally, and examination of the fundus revealed a mass indenting the inferior aspect of the globe. Thedog did not have signs of pain when the mouth was opened. The dog was referred, and magnetic resonance images(MRI) were obtained (Fig 1).

Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turnthe page **

Figure 1—Coronal (A) and transverse (B) magnetic resonance images of a 10-year-old castrated male Springer Spaniel evaluatedbecause of a 2- to 3-month history of a prolapsed and swollen right nictitating membrane.

VETERINARY MEDICINE TODAY

This report was submitted by Kelly Caruso, VMD; Ruth Marrion, DVM, PhD, DACVO; and Gena Silver, DVM, MS, DACVIM; from the InTownVeterinary Group, 247 Chickering Rd, North Andover, MA 01845. Dr. Caruso’s present address is Animal Eye Clinics, 8023 Piney Branch Rd,Silver Springs, MD 20910.

Address correspondence to Dr. Caruso.

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1554 Vet Med Today: What Is Your Diagnosis? JAVMA, Vol 221, No. 11, December 1, 2002

DiagnosisMRI diagnosis—Retrobulbar mass indenting the

inferior aspect of the right globe. The mass involved theoptic nerve but did not appear to invade the cranial vault;the inferior aspect of the mass was less defined (Fig 2).

CommentsDifferential diagnoses for this retrobulbar mass includ-

ed neoplasia (meningioma, nerve sheath tumor, fibrosarco-ma, lymphoma, fibroma, osteosarcoma, mastocytoma, andosteochondrosarcoma), retrobulbar abscess, myositis, andcellulitis. Abscess, myositis, and cellulitis were less likelydiagnoses because of the absence of signs of pain. On thebasis of these differentials, the location of the lesion, theabsence of pain, and the age of the dog, exenteration andhistologic evaluation were recommended.

Histologic evaluation of multiple tissue sectionsderived from the right eye and orbit revealed severechronic-active periocular cellulitis with myositis.Foreign material compatible with plant material wasseen on 1 of the tissue sections. No evidence of malig-nant cells or fungi was seen. The final diagnosis wascellulitis with myositis caused by retrobulbar plantmaterial. The dog recovered from surgery withoutcomplications, and was doing well at the postoperativesuture removal 10 days later.

Orbital disease causes variable displacement of theglobe and protrusion of the nictitating membrane. Tumorsrepresent a common group of orbital diseases. Althoughthis dog did not have a tumor, the history, clinical signs,and MRI findings were highly suggestive of neoplastic dis-ease. Orbital tumors can originate from any orbital tissueand are mostly primary and malignant. In general, orbitalneoplasms develop in older animals. The mean age isapproximately 9.5 years, compared with 4 years in cases oforbital abscesses. In most instances, the prognosis isguarded at best. Most dogs with orbital neoplasms areeuthanatized shortly after diagnosis. Survival time canincrease with early diagnosis and surgical intervention.1

Determining the cause of orbital disease can bedifficult. Radiography can be used to determine theextent of disease affecting the orbit, but multipleviews are often necessary, and etiology of the disease isdifficult to determine using this imaging modality.Radiographic images are also subject to tissue summa-tion artifact in the skull. Orbital ultrasonography isuseful in localizing lesions but is not generally usefulfor determining tissue of origin or malignancy. Forexample, in 1 report,2 ultrasonographic images ofchondrosarcoma and zygomatic salivary adenitis weresimilar, and in a report2 of retrobulbar lymphoma in acat, the initial diagnosis was retrobulbar abscess.Computed tomography (CT) has been reported2 toclearly define the anatomy of normal and abnormalorbital structures in dogs and has been used to evalu-ate orbital neoplastic disease in cats. Bony lysis on CTscan appears to be associated with neoplasia in dogsand cats.2,3 Three-dimensional location of intracranialneoplasms can be determined by viewing cross-sec-tional images in succession. Computed tomographycan be helpful in identifying the type and extent oforbital disease but generally does not delineate bor-ders of a mass within the calvarium.2 Magnetic reso-nance imaging provides spatial and soft-tissueresolution and contrast of the periocular and orbitalregion that is superior to the images acquired usingCT. Magnetic resonance imaging is used after CT inhumans to further define a soft-tissue component ofneoplasms of the calvarium.2

1. Spiess BM, Wallin-Hakanson N. Diseases of the canineorbit. In: Gelatt KN, ed. Veterinary ophthalmology. Philadelphia: Lea& Febiger, 1999;511–533.

2. Ramsey DT, Gerding PA, Losonsky JM, et al. Comparativevalue of diagnostic imaging techniques in a cat with exophthalmos.Vet Comp Ophthalmol 1994;4:198–202.

3. Calia CM, Kirschner SE, Baer KE, et al. The use of comput-ed tomography scan for the evaluation of orbital disease in cats anddogs. Vet Comp Ophthalmol 1994;4:24–27.

Figure 2—Same magnetic resonance images as in Figure 1. Notice the retrobulbar mass (arrowhead) indenting the inferior aspect of the right globe.

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