Ultrasound of the Month: Ocular Abscess

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THE CASE

A female in her 60’s with a remote history of bilateral cataract surgery presented to the emergency department (ED) with a two-week history of right eye swelling. Six days prior, the patient was evaluated at an urgent care and prescribed doxycycline and prednisone. She was re-evaluated over the following days and was transitioned from doxycycline to cephalexin.  She presented to our ED due to progressive swelling which was now preventing her from closing her eye. Over the preceding 24 hours she also developed a  pressure-like sensation around her eye and a right frontal headache. She also reported pain in the eye itself which she described as a foreign body sensation. She endorsed blurred vision in her right eye, but denied double vision, photophobia, pain with ocular movements, fevers, chills, congestion, or nasal drainage. She denied any use of contact lenses or any recent trauma to the eye. 

Physical examination revealed a female in no distress with normal vital signs. A focused ocular examination revealed significant erythema, edema, and tenderness of the right periorbital region and the conjunctiva demonstrated mild chemosis. Her pupils were symmetric with symmetric, minimal reactivity. The right globe was displaced inferiorly in the socket and ptosis was appreciated. A slit lamp examination demonstrated a small area of uptake over the inferior aspect of the right cornea. Her visual acuity was 20/40 on the right eye, 20/20 on the left eye. Ocular pressure was 13 mmHg in the right eye and 11 mmHg in the left eye. 

Ocular point-of-care-ultrasound (POCUS) was performed as seen below. At the superior border of the globe, thickening and cobblestoning of the orbital soft tissue was appreciated along with a spherical anechoic collection with internal echogenic debris. These findings were interpreted by the treating emergency physicians to be consistent with an intraorbital abscess. These findings were corroborated on CT imaging performed during the same encounter, which additionally demonstrated severe pansinus disease. 

The patient was started on intravenous (IV) vancomycin, cefepime, and metronidazole and ophthalmology was consulted. The patient underwent an anterior orbitotomy with ophthalmology and was admitted to medicine for continued IV antibiotics and treatment of her corneal abrasion. During her admission, otolaryngology (ENT) was consulted given the concern for a primary sinonasal source. She underwent nasal endoscopy which demonstrated significant purulence within her maxillary sinuses and mild purulence in her frontal and ethmoid sinuses, for which she underwent maxillary antrostomy and ethmoidectomy.  Tissue cultures obtained in the operating room grew nonspecific gram positive cocci in chains and pairs and gram positive bacilli. The patient was transitioned to a 10 day course of cefpodoxime and was discharged on hospital day 3 with ENT and ophthalmology follow up.

DISCUSSION

Orbital abscess is a rare and vision threatening complication of orbital cellulitis. Orbital abscess, similarly to orbital cellulitis, involves infection of the contents of the orbit, fat, and extra ocular muscles. In comparison to orbital cellulitis itself, orbital abscess is more likely to present with proptosis and asymmetry (1). The etiology of these orbital infections is typically due to extension of a sinus infection or in more rare cases, odontogenic infections (2). Prompt recognition of orbital abscess from other orbital infections is necessary, as source control via surgical drainage is recommended in addition to antibiotics. Our patient underwent anterior orbitotomy, but there are case reports in the literature of ultrasound-guided drainage (4). 

MRI is the ideal imaging modality for soft tissue evaluation. However, MRI is not universally available in the emergency department, is costly, and can be delayed due to contraindications and need for sedation. CT of the orbits with thin cuts has become the test of choice for diagnosis of ocular infections. A plethora of data has highlighted the advantage of bedside ocular ultrasound in facilitating and expediting a diagnosis, reduced cost and reducing exposure to radiation (8, 9, 10). Brzycki et al. published a retrospective study conducted over a seven year period that showed that when POCUS was utilized in patients with suspected periorbital and orbital infections, there was appropriate initiation of antibiotics in 100% of subjects, initiation of early consultation in 68% of subjects, and avoidance of unnecessary additional imaging in 13% of subjects (11). In addition, there are studies that discuss missed cases of abscess on CT that were detected with use of ultrasound. Kaplan et al. compared the performance of CT to US for diagnosis of subperiosteal abscess and found two missed cases of abscess with use of CT that were detected with use of ultrasound. The authors delineate how multiple studies have demonstrated similar occurrences (12). 

Performing an ocular ultrasound requires preparation and caution. The main contraindication to that exists includes high clinical suspicion for globe rupture (14). Ocular ultrasound should be performed with the use of a high frequency linear probe. The current recommendation is to select the machine's ophthalmic or ocular setting as seen in Image 1, which will reduce the mechanical and thermal effects and minimize any potential harm (15, 16). The patient should lie supine or partially upright with their eyes closed. A generous amount of ultrasound gel should be applied over the eyelid to minimize the need for pressure. Marks et al studied the use of an occlusive dressing over the eyelid prior to application of gel, but found reduced image quality with no significant difference in patient discomfort (17). The transducer can then be applied over the gel, with use of the 5th digit or other parts of the hand to provide stability. The eye can then be scanned in both transverse and longitudinal planes, and in both neutral position and with active motion of the eye (18).

An orbital abscess will share resemblance to abscesses seen elsewhere on the body, typically an anechoic or isoechoic fluid collection with echogenic borders (9). Due to the limited space surrounding the eye and orbit, an abscess can be seen causing mass effect on surrounding structures. The “guitar pick” sign can be appreciated using ultrasound and has been described in the literature, occurring from increased intracranial pressure in the retrobulbar space leading to distortion of the spherical globe (16, 19). 

CONCLUSION

While growing, the current literature documenting the utilization of POCUS in evaluation of orbital and periorbital infections is minimal. As emergency physicians, both ocular and soft tissue ultrasonography are well within our purview and can aid in diagnostic certainty and expedite treatment in patients presenting with signs and symptoms of orbital infections. This case serves to highlight the feasibility of POCUS as a diagnostic aid in periorbital and orbital infections and demonstrate the sonographic findings of this infrequent orbital infectious entity. 

AUTHORED BY MARTINA DIAZ MCDERMOTT, MD

Dr. Diaz McDermott is an Ultrasound Fellow in the Department of Emergency Medicine at the University of Cincinnati and the Editor of Taming the SRU: Ultrasound of the Month.

PEER REVIEW BY Meaghan Frederick, MD and Lori Stolz, MD

Dr. Minges is an Ultrasound Fellowship trained Assistant Professor in Emergency Medicine at the University of Cincinnati.