RETROBULBAR ABSCESS IN A DOG

History

A four year old female English Springer Spaniel, 55 days post mating and heavily pregnant, presented with sudden onset lower lid swelling and third eyelid protrusion on the right eye for the last 24 hrs. The dog was rubbing at the eye.

Examination

A full clinical examination was undertaken with an ophthalmic examination as per Appendix 1. Clinical examination was unremarkable apart from pain on mouth opening.

All relevant findings are recorded below.

OS: - Unremarkable

OD: - Lower lid swelling

- Hyperaemic and congested conjunctiva

- Protruding third eyelid

- Patchy bruising to external surface of third eyelid

- Central corneal fluorescein dye retention 4 mm x 6mm (fig. 29)

- Moderate exophthalmos

- Moderate lagophthalmos

- Pain and resistance to globe retropulsion

STT L = 20mm/minute. R = 25mm/minute

IOP L = 16 mmHg, R = 12 mmHg

Figure 29: On presentation.

Diagnosis

Unilateral retrobulbar space occupying lesion:

- Abscess / cellulitis

- Granuloma (foreign body / fungal)

- Cyst

- Neoplasia

- Haemorrhage

- Arteriovenous shunt

- Myositis

- Sialocoele

Further Tests

Radiography of the upper right dental arcade was unremarkable.

Ocular ultrasonography revealed a hypoechoic area medial to the cone of ocular muscles displacing the cone laterally.

Diagram 3: Ultrasonographic image obtained with 10MHz linear probe through the globe. Large hypoechoic lesion medial in orbit visible.

Treatment

Amoxycillin with clavulanic acid (Synulox, Pfizer) 15 mg/kg BID PO for 10 days Carprofen (Rimadyl, Pfizer) 2 mg/kg BID PO for 7 days

General anaesthesia was performed as per Protocol 1, Appendix 2. The pharynx around the endotracheal tube was packed with swabs. A small incision was made in the gingiva in the depression caudal to the last right upper tooth. Fine, blunt artery forceps were introduced, aiming caudal to the globe, dorsally and gentle probing was performed. These were replaced by crocodile forceps to allow longer reach but no grabbing actions were performed with the jaws (fig. 30). No purulent material was observed within the surgical site. A swab was taken from within the surgical track for bacteriology. A temporary tarsorrhaphy was performed using 2 metric Polyglecaprone (PDS II Ethicon). The incision was not sutured.

Figure 30: During surgery.

Follow up

No pathogens were isolated from the swab taken at surgery. The tarsorrhaphy was released 4 days post surgery at which time all clinical signs had resolved apart from some conjunctival hyperaemia.

Discussion

Exophthalmos is a not uncommon presentation and must be carefully distinguished from buphthalmos. In this case the exophthalmos was corroborated by the normal intraocular pressures measured and third eyelid protrusion, suggesting an extraconal, retrobulbar problem.

Retrobulbar disease in the dog and cat, due to the incomplete nature of the bony orbit, can present as pain on opening the mouth as movement of the vertical ramus of the mandible applies pressure to the orbital contents (1). Complicating the issue in this case was the fact that the bitch had already lost body condition due to the advanced stage of pregnancy. Immediate resolution of the problem was therefore vital to avoid a prolonged period of inappetance.

The sudden onset and severity of the unilateral clinical signs, coupled with the ultrasonographic findings of a hypoechoic area behind the globe strongly suggested a retrobulbar abscess. Differentiation between cellulitis and abscessation is not usually required unless a very thick wall is present around the abscess requiring surgical intervention with direct visualisation of the lesion.

Ultrasonography is a useful tool to investigate retrobulbar disease, in part because it is so easily performed in the conscious patient, either directly through the cornea after topical anaesthesia or through the upper lid (2). The retrobulbar space is very complex with many small but significant structures within it. Most of these are difficult to identify individually but together they form a recognisable "cone" of tissue. Disruption of the cone is easier to identify (3).

As an infectious cause was suspected the case could possibly have been managed conservatively initially with antibiotics and pain relief to avoid surgery in a gravid patient. The trauma to the conjunctiva of the third eyelid and corneal ulceration due to lagophthalmos meant a tarsorrhaphy was necessary to protect these structures. It also provided a degree of tamponade on the retrobulbar space. Since general anaesthesia was required for this procedure then drainage of the site could be attempted at the same time. It is common not to get a significant release of pus as in this case. Lavage of the area can be attempted however there is some suggestion that this may track infection along tissue planes so was not performed in this case.

No significant growth was obtained from the sample taken at surgery. It is possible probing had not opened into the fluid pocket seen on ultrasound, but because a route of drainage to the site had been established, the infection drained later, assisted by the tamponade of the tarsorrhaphy. Broad spectrum antibiotics were given but if the management had not proved successful an attempt could have been made to directly aspirate the fluid to gain a sample for bacteriology (4). Aspiration may be attempted blindly via the oral drainage route, however in this case could probably have been performed at the medial conjunctival fornix, under ultrasound guidance.

Radiographs were taken prior to surgical drainage to see if there was any dental disease extending into the retrobulbar space e.g. tooth root abscessation. If that was the case extraction of the tooth would have provided drainage and resolution of the problem (5). Care must be taken in dental extractions caudal in the upper dental arcade to avoid slippage and deep penetration of dental elevators into the orbit which may damage the orbital contents directly or introduce infection.

Post scriptum: Ten days after surgery the bitch whelped eleven healthy puppies.

References

1. Mould JRB (2002) The orbit and globe. In BSAVA Manual of Small Animal Ophthalmology 2nd ed.

2. Morgan RV (1985) Ultrasonography of retrobulbar diseases of the dog and cat. Journal of the American Animal Hospital Association 25, 393-399.

3. Burk RL, Ackerman N (1996) The Skull. In: Small Animal Radiology and Ultrasound 2nd ed. WB Saunders.

4. Boydell P (1991) Fine needle aspiration biopsy in the diagnosis of exophthalmos. Journal of Small Animal Practice 32, 542-546.

5. Ramsay DT, Maretta SM, Hamor RE, Gerding PA, Knight P, Johnson JM, Bagley LH (1996) Ophthalmic manifestations and complications of dental disease in dogs and cats. Journal of the American Animal Hospital Association 32, 215-224.