Orbital and Subcutaneous Emphysema Following Enucleation and Respiratory Distress in a Japanese Chin

Introduction

Orbital emphysema is an uncommon complication occurring after enucleation in brachycephalic dogs. To the authors' knowledge, this is the first case report to document acute exacerbation of orbital emphysema following an episode of respiratory distress. Additionally, the diagnostic and therapeutic approaches for this condition are outlined. This is the first report to document the use of computed tomography (CT) to confirm the presence of orbital and subcutaneous emphysema. This case highlights the importance of addressing the nasolacrimal duct when performing an enucleation in a brachycephalic dog.

Case Report

A 3 yr old, 4.75 kg, neutered male Japanese chin was initially presented to the Cummings School of Veterinary Medicine at Tufts University (CSVMTU) in June 2009 for evaluation of a waxing and waning swelling of the left orbit, which worsened acutely. The owner reported the dog was lethargic, anorexic, and painful. One yr previously, the left eye was enucleated by the referring veterinarian as a result of proptosis, which occurred following an altercation with a German shepherd dog.

Physical examination upon admission to the CSVMTU revealed a temperature of 40.1°C. A large, soft, fluctuant swelling was noted at the site of the previous enucleation; the skin surrounding the site was intact but erythematous. The dog was painful on palpation of the area. The remainder of the physical examination was unremarkable. Initial diagnostic tests performed included a complete blood count, a blood gas/electrolyte panel, and ultrasound of the orbital region. On complete blood count, all values were within normal reference intervals. Neutrophil toxicity was noted on cytologic evaluation of a blood film. The blood gas/electrolyte panel was unremarkable, aside from a moderate elevation of lactate (5.8 mmol/L [normal = 0.3–1.0 mmol/L]). Ultrasound of the left orbital region demonstrated a hypoechoic fluid pocket. Aspiration yielded purulent material that was submitted for cytology and bacterial culture (aerobic and anaerobic). Degenerate neutrophils and 4+ cocci were observed on cytologic evaluation. Coagulase-positive Staphylococcus was grown on aerobic bacterial culture, while the anaerobic bacterial culture yielded no growth. Therapy included clindamycin^a (10 mg/kg, per os [PO], q 12 h), enrofloxacin^b (10 mg/kg, PO, q 24 h), tramadol^c (2 mg/kg, PO, up to q 8 h), and application of a warm compress (2–4 times daily). The owners were instructed to return in 1 to 2 wk for re-evaluation. The possibility of performing additional diagnostic tests, such as CT, and surgical exploration of the orbit was discussed with the owners.

Twelve days later, the dog returned to the CSVMTU with marked improvement of his clinical signs. Examination revealed that the swelling had largely resolved and no pain was appreciable upon palpation. The dog was discharged with instructions to finish the course of antibiotics and to return to the CSVMTU in 1 mo, or sooner if symptoms recurred.

The dog was lost to follow-up until January 2013, when he presented to the CSVMTU neurology service with a 2 mo history of back pain. Physical examination demonstrated mild paraparesis and ataxia, with hyperesthesia on palpation of the cervical spine. Throughout the examination, the dog had multiple episodes of inspiratory stridor and intermittent cyanosis when stressed or excited. Stenotic nares were noted and an elongated soft palate was suspected due to the facial conformation and the stridorous breathing. A moderate orbital swelling was noted at the site of the previous enucleation. The owners reported the swelling had continued to wax and wane but had remained relatively unchanged over the past 4 yr. Results of a complete blood count and serum chemistry were within normal reference intervals. Thoracic radiographs were performed and no significant abnormalities were detected. Based on history and initial physical examination findings, intervertebral disc disease (IVDD) was the primary differential diagnosis for the dog's back pain. However, infectious, inflammatory, and neoplastic disease could not be ruled out. Advanced imaging of the cervical and thoracic spine was recommended to determine the source of the spinal pain. Additionally, due to the frequency of the respiratory episodes, surgical correction of the soft palate and stenotic nares was recommended. The dog was anesthetized and the elongated soft palate confirmed. MRI of the cervical and thoracolumbar spine was performed followed by a cerebrospinal fluid tap. In addition, a soft palate resection and alar wedge resection were performed. The owners were given the option to further evaluate his orbital swelling at that time, but they declined further diagnostics since the swelling had been stable and non-painful.

MRI results were consistent with IVDD, with mild-to-moderate extradural compression noted at T11-12. The cerebrospinal fluid tap was unremarkable. Medical management was elected to treat the IVDD, with the recommendation to consider surgery if the dog did not improve with pain medications and cage rest. The dog was hospitalized overnight and discharged with tramadol^c (5 mg/kg, PO, q 12 h), carprofen^d (2.6 mg/kg, PO, q 12 h), gabapentin^e (10 mg/kg, PO, q 8 h), and amantadine^f (4 mg/kg, PO, q 24 h) for medical management of the IVDD.

Four days after discharge from the hospital, the dog presented to the ophthalmology service at the CSVMTU for evaluation of acute worsening of the left orbital swelling. According to the owners, the dog was lethargic, hyporexic, and the owners felt a “crackling” when touching the head and neck. Physical examination identified a non-painful, moderate-to-severe, soft, fluctuant swelling of the left orbital region with erythema of the overlying skin (Figure 1). Crepitus was noted over the occipital tuberosity. The dog's neurologic examination demonstrated improvement with only mild reaction upon palpation of the spinal region. The physical examination was otherwise unremarkable. Given the acute worsening of the orbital swelling, additional diagnostics, including an orbital ultrasound or CT scan, were recommended. The dog was placed under general anesthesia and a CT scan of the head was performed. Images were obtained pre- and post-intravenous injection of 2 ml/kg of Iohexol^g contrast agent. The CT scan demonstrated a large volume of gas (4 cm in length × 3.2 cm in height × 3.5 cm in width) occupying the left orbital space. The gas was noted to extend caudally within the subcutaneous tissues to the right and left hemimandibles, dorsal to the cranium, and partially surrounded the cranial neck (Figures 2, 3). Additionally, thoracic radiographs were performed to rule out pneumomediastinum and pneumothorax secondary to possible tracheal tear or trauma as a source of the subcutaneous emphysema. Thoracic radiographs defined the degree of the subcutaneous emphysema, which extended from the second thoracic vertebra through the cranial extent of the area imaged and ventrally to the mid-humerus. On the lateral projection, a small pocket of air could be seen overlying the cranial mediastinum, but was suspected to be related to extension of subcutaneous gas. No evidence of pneumothorax was noted on either radiographic projection.

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The dog was subsequently taken to surgery for exploration of the left orbit. A 5 cm skin incision was made over the previous surgical scar. Upon opening the incision, an air-filled, cyst-like structure was observed to completely encompass the orbital space (Figure 4A). The structure, lined by mucosa, was removed en bloc and placed in 10% formalin for histopathologic evaluation. Following removal of this tissue lining, the orbit was copiously lavaged with dilute betadine solution followed by saline lavage. The nasolacrimal duct was identified and confirmed to be patent following cannulation with 2-0 nylon^h suture (Figure 4B). Injection of dilute fluorescein was attempted through the canaliculus; however, no evidence of fluorescein was seen exiting from the nares. The nasolacrimal duct opening was sutured using 4-0 polyglactin 910ⁱ with a single cruciate suture. The orbital fascia was then closed with 4-0 polyglactin 910ⁱ in a simple, continuous pattern followed by a simple, continuous oversew incorporating the subcutaneous tissues. A simple, continuous intradermal pattern was placed, and skin glue^j was used as needed. The dog recovered uneventfully from anesthesia and was hospitalized overnight with continued intravenous pain medication and antibiotics. He was discharged the following day with a 2 wk course of amoxicillin/clavulanic acid^k (14 mg/kg, PO, q 12 h) and instructions to continue the medications for the IVDD as previously prescribed.

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Histopathology of the cyst-like lining from the orbit demonstrated a mixture of fibrovascular and adipose tissue mixed with skeletal muscle, nerves, tubuloacinar gland, a focus of cartilage, and an area of hyperplastic conjunctival epithelium. Interstitial edema, multifocal hemorrhage, and a moderate infiltration of mixed leukocytes (neutrophils, lymphocytes, plasma cells, and histiocytes) were seen. These findings were consistent with an inflamed cyst wall and contained features indicative of a previous enucleation site. Remnants of tissue that should have been completely removed during the initial enucleation surgery were identified. These included an area of conjunctival epithelium, which previously lined the inside of the eyelids and covered the globe to the limbus; a remnant of tubuloacinar gland, presumed to be the gland of the third eyelid, which is involved in aqueous tear production; and a focus of hyaline cartilage from the T-shaped cartilage present within the nictitating membrane.

The dog presented to the CSVMTU 8 wk later for recheck. Physical examination demonstrated no evidence of orbital swelling (Figure 5) and no pain on manipulation of the surgical site. The owners reported that the dog was behaving normally at home and had experienced no episodes of swelling or pain since the surgery was performed. The dog's spinal pain had completely resolved. All medications were discontinued, and the dog was discharged with no requirement to follow up unless any swelling, pain, or discharge was noted in the future.

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Discussion

Orbital emphysema is a condition that is rarely reported in the veterinary literature. It may occur following trauma involving rupture of the frontal or paranasal sinuses.^1,2 However, it is more likely to be seen as a complication following routine enucleation, with brachycephalic breeds being most commonly affected.^3,4 It is postulated that high positive pressure within the nasal cavity generated during exhalation, combined with a patent nasolacrimal duct system, results in retrograde movement of air into the orbital space. This process is thought to be exacerbated by the presence of stenotic nares and elevated intranasal pressure.^2,5,6 Alternatively, air entrapment due to masticatory movements may create a “bellows” effect within the orbital space.⁵ An elongated soft palate may play a role by directing air into a constricted nasal cavity through a patent nasolacrimal duct.⁵ Regardless of the underlying mechanism, the result is entrapment of air within the orbital space and subsequent swelling of the surrounding soft tissues.⁴

Remnants of conjunctival tissue from the initial enucleation surgery may have led to the formation of an orbital abscess and subsequent orbital emphysema. While conjunctival remnants, due to their secretory nature, are more often associated with the development of orbital cysts, their presence in the current case likely prevented normal scarring of the nasolacrimal system from occurring.³ This consequently allowed for retrograde movement of air into the orbital cavity. In support of this, a recent report described three cases in which residual conjunctival tissue was attributed to various postoperative complications, including a nictitans inclusion cyst, orbital pneumatosis, and a conjunctival mucocele.⁷ The majority of cases of orbital emphysema that occur following enucleation spontaneously resolve.⁴ However, surgical removal of any remaining conjunctival tissue and ligation of the patent proximal nasolacrimal duct have been recommended for persistent cases.^3,7 Injection of sclerosing agents, such as tetracycline, into the orbit followed by the use of pressure wraps has also been reported as a treatment option.⁸

The presence of a waxing and waning orbital swelling with an acute exacerbation after an episode of respiratory distress made orbital emphysema the primary differential diagnosis in this patient. Other differential diagnoses included the presence of an orbital fluid-filled cyst, orbital cellulitis, seroma, abscess, hemorrhage, or neoplasia. Advanced imaging was performed to confirm the presence of emphysema and the absence of other significant lesions prior to proceeding to corrective surgery. Previous case reports have also documented the use of skull radiographs as a viable method to identify air within the orbital cavity.^5,6,9 Alternatively, injection of sodium fluorescein into the orbital cavity may document the presence of a patent nasolacrimal duct.^5,6,9

Increased respiratory effort has been previously suggested as a predisposing risk factor for the development of orbital emphysema in dogs, and one case report documents orbital swelling following periods of exercise.^5,10 However, there have been no published reports directly correlating an episode of increased respiratory effort with orbital swelling. While the patient's orbital swelling had historically waxed and waned in severity, signs acutely worsened after surgical correction of the stenotic nares and elongated soft palate, which resulted in a marked increase in the extent of air entrapment. To the authors' knowledge, this is the first report documenting acute worsening of emphysema caused by a patent lacrimal duct after surgical correction of the brachycephalic airway syndrome.

In dogs, subcutaneous emphysema most frequently results from tracheal tears or ruptures secondary to motor vehicle accidents, tracheal pressure necrosis, or bite wounds.^11,12,13 The dog in this case report had no known history of recent trauma. Although tracheal trauma from recent anesthesia and intubation was a consideration, no evidence of leakage of air from the trachea or free air within the thoracic cavity was noted on thoracic radiographs. Alternatively, the source of the subcutaneous gas in this dog may have resulted from leakage through the medial wall of the orbit, where the frontal, lacrimal, and palatine bones join.² While extension of air has not been previously reported to occur via this route, infectious and neoplastic migration from the sinus or nasal cavity have been reported to occur in this manner.² However, the most likely explanation for this patient was leakage of air into the orbit though a patent nasolacrimal duct.

Conclusion

This is the first case report to document acute progression of orbital emphysema with extension of subcutaneous emphysema into local soft tissues following an episode of respiratory distress in a dog. This highlights the importance of addressing the nasolacrimal duct with either electrocautery or suture material while performing enculeations in brachycephalic dogs. It is also critical that all conjunctival tissue be removed from the orbit prior to closing the incision during any enucleation surgery.