Multiple Follicular Cysts of the Ear Canal in a Dog

Introduction

Follicular cysts, epidermal inclusion cysts, epidermal cysts, epidermoid cysts, and infundibular cysts are responsible for 33% and 50% of the non-neoplastic, noninflammatory, tumor-like lesions removed from dogs and cats, respectively.¹ Follicular cysts occur most frequently in middle-aged to older dogs, and they often are located on the dorsum and extremities.¹ To the authors’ knowledge, follicular cysts originating from the external ear canal have not been reported in dogs. The purpose of this report is to describe the presentation, diagnostic workup, surgical treatment, and outcome of recurrent otitis externa and media secondary to multiple aural follicular cysts in a dog.

Case Report

An 11-year-old, 18-kg, neutered male standard schnauzer was referred to our institution for chronic otitis externa and para-aural swelling and fistulation of the right ear. Six months prior to referral to us, the dog was presented to the referring veterinarian for swelling at the base of the right ear. At that time, the dog was treated with amoxicillin/clavulanic acid^a at 22 mg/kg orally q 12 hours for 1 month, and the swelling temporarily resolved. Swelling recurred and was obvious at the time of reevaluation by the referring veterinarian 2 months after the initial examination.

Skull radiographs were performed by the referring veterinarian, and they revealed a small (2 cm) mass at the base of the right ear. The mass was aspirated, and a tentative diagnosis of an abscess was made. The mass was explored, opened, and drained; samples were submitted for bacteriological evaluation. Aerobic culture revealed Staphylococcus intermedius sensitive to amoxicillin/clavulanic acid^a and enrofloxacin, ^b which were administered at 22 mg/kg and 2.5 mg/kg, respectively, orally q 12 hours for 1 month. The swelling temporarily resolved. Two months after discontinuation of antimicrobial therapy, swelling reappeared in addition to a ventral para-aural fistula. The referring veterinarian obtained a biopsy at that time, which showed chronic active cellulitis. Staphylococcus intermedius and Corynebacterium spp. were isolated, and the dog was prescribed cephalexin^c (20 mg/kg orally q 8 hours for 2 months). No improvement in clinical signs was noted, and the dog was referred.

Upon presentation to the dermatology service, physical examination revealed severe stenosis of the horizontal portion of the right ear canal and a small (3 cm), firm, subauricular mass located at the base of the right ear. A para-aural fistula and purulent discharge were also present at the right ear base. Otoscopy of the left ear canal and tympanic membrane was unremarkable, but otoscopic examination of the right ear canal was impossible to perform because of the severe stenosis of the horizontal portion of the ear canal. The right submandibular lymph node was moderately increased in size. The complete blood count and serum biochemical profile were within normal limits.

Upon reviewing the skull radiographs forwarded from the referring veterinarian, a small (2 cm) mass at the base of the right ear was observed. Dystrophic mineralization of the horizontal and vertical right ear canal was seen, as well as mild to moderate thickening of the right tympanic bulla (bulla osteitis). Ultrasound (using a 5- to 8-MHz broadband-width sector probe and ultrasound machine^d) of the right para-aural region was performed in an attempt to define the origin and extent of the subauricular mass, to eliminate the possibility of a foreign body, and to obtain samples for cytological evaluation. Ultrasound examination revealed that the mass was well defined and represented a severe focal dilatation of the horizontal ear canal (2.4 cm, approximately four times the diameter of the left ear canal), which contained heterogeneous and highly hyperechoic material with acoustic shadowing [Figures 1A–1C]. Hyperechoic interfaces with acoustic shadowing were seen within the wall of the ear canal, representing dystrophic mineralization. Ultrasound-guided fine-needle aspiration was performed, and cytological evaluation of the ear canal material was compatible with a keratin-producing cyst or tumor in combination with a secondary infection.

To further determine the extent of the disease and to plan surgical treatment, magnetic resonance imaging (MRI) was performed under general anesthesia with a 1.5 Tesla superconducting magnet and dedicated head coil.^e The following image sequences were obtained: transverse pre- and post-contrast (gadobenate dimeglumine^f 0.1 mmol/kg intravenously [IV]), fast-spin echo (FSE), T1-weighted (w), FSE-T2w, FSE-T2w with fat saturation (FS), fluid-attenuated inversion recovery (FLAIR), gradient recalled echo (GRE-MERGE), dorsal FSE-T2w with FS, postcontrast FSE-T1w, and sagittal FSE-T2w [Figures 2A-2C, 3A-3D].

Examination of the MRI scans revealed severe dilatation of the horizontal portion of the right ear canal. Within the focal dilatation was heterogeneous material with mixed signal intensity (predominantly T2w and FLAIR hyperintensity, intermediate granular T1w intensity, and signal suppression during fat-suppression sequences) and no contrast enhancement. No evidence of magnetic susceptibility on the gradient echo sequence was seen, indicating that the material within the focal dilatation did not have a hemorrhagic or mineralized component. An abnormal tissue extended into the right tympanic bulla and epitympanic recess, where the signal became more homogeneous and was hyperintense on T1w and T2w images without signal suppression during fat suppression. Moderate heterogeneous enhancement of this tissue was seen. A well-defined, 3 mm-diameter, cutaneous fistula extended from the ventro-lateral portion of the right ear canal to the cutaneous surface. The walls of this fistula were hyperintense on T2w images and enhanced intensely. The ear canal walls and those of the fistula had the same signal characteristics. The dorsolateral aspects of the horizontal portion of the ear canal and the entire vertical portion of the ear canal were difficult to identify on MRI because of the severe stenosis of the canal. The ipsilateral medial retropharyngeal lymph node was also enlarged.

Based on the collective diagnostic test results, the dog was diagnosed with retention of sebaceous or ceruminous material, para-aural fistulation, and otitis media and externa. All conditions were secondary to severe ear canal stenosis. A total ear canal ablation with lateral bulla osteotomy (TECA-LBO) was recommended and authorized by the owners. The TECA-LBO of the right external ear canal was performed under general anesthesia as previously described, with two modifications:^2–6 (a) an elliptical skin incision was made around the vertical portion of the ear canal orifice, including the fistula orifice, and (b) fistula identification was facilitated by catheterization, which further confirmed communication of the cutaneous fistula with the vertical ear canal. Only one complication was encountered during surgery: the facial nerve was tightly adhered to the ventral portion of the horizontal canal, and it had to be dissected and retracted to permit completion of the TECA. After copious lavage with 0.9% saline, the surgical site was primarily sutured. Primary closure with a simple interrupted suture pattern using 3-0 polydioxanone^g was performed to decrease the amount of dead space. A continuous intradermal suture pattern using 4-0 polyglecaprone 25^h was then used, and the skin incision was closed in a “T” pattern with a simple interrupted suture of 3-0 nylonⁱ [Figures 4A, 4B].

The excised tissues (i.e., the external ear canal including the fistula and epithelial biopsies from the tympanic bulla) were submitted for histological examination and a bacterial culture. Histopathology results revealed a chronic otitis externa and media with marked fibrosis and multiple follicular cysts. An expansive mass was visualized, which was partially bordered by keratinized epithelial cells that were multifocally acanthotic and necrotic with mild orthokeratosis [Figures 5A, 5B]. A population of neutrophils, macrophages, lymphocytes, and plasmocytes were multifocally infiltrating the dermis. Several distended hair follicles with keratin inclusions, adipocytes, and fibrous tissue constituted the mass, which also contained several distended ceruminous glands with granular acidophile material. Mineralizations were also visualized along the squamous cells and cellular debris. Orthokeratosis and infiltration of neutrophils and macrophages extending to the tympanic bulla with necrotic cells and cellular debris were also present. Staphylococcus intermedius and Enterococcus spp. were isolated; both were susceptible to amoxicillin/clavulanic acid.^a

Postoperative care consisted of applying a loose, padded head bandage to cover the surgical site for 2 days. Because bandages may reduce pharyngeal airway size and thereby cause suffocation in the early postoperative period, respiration was closely monitored for the first 24 hours postsurgically. An Elizabethan collar was used to reduce self-mutilation until the sutures were removed (at 14 days). During bandage changes, the wound was examined for evidence of fluid accumulation or signs of infection. The dog received a continuous IV infusion of fentanyl^j (5 μg/kg per hour) postoperatively for 24 hours, hydromorphone hydrochloride^k (0.05 mg/kg IV q 4 hours) for 24 hours, and then meloxicam^l (0.1 mg/kg orally q 24 hours for 5 days). Antibiotic therapy using cephalexin^c (20 mg/kg orally q 8 hours) was administered for the 3 days following the surgery while bacteriological results were pending. Antibiotic therapy was then changed to amoxicillin/clavulanic acid^a (22 mg/kg orally q 12 hours for 3 weeks) based on the bacteriological culture results and antimicrobial susceptibility testing.

A weak and incomplete right palpebral reflex was noted immediately after surgery, which was presumably caused by facial nerve paresis. Artificial tears were applied for 7 days until the affected eyelid regained satisfactory function.

Reevaluation at the time of suture removal (at 14 days) by the referring veterinarian revealed identical facial nerve paresis with a weak and incomplete palpebral reflex and a dropped upper right lip with decreased muscle tone. The surgical incision had healed without any complications. Communication with the owners at >12 months postoperatively confirmed continued presence of facial nerve paresis with the same weak and incomplete palpebral reflex; however, artificial tears were not needed. The tone in the lip was almost back to normal, and the dog was otherwise asymptomatic.

Discussion

Otitis externa is the most common ear disease of the dog and cat and is estimated to affect 5% to 20% of the canine population.^7,8 Otitis media is often an extension of otitis externa, and the incidence of otitis media in dogs with chronic otitis externa has been reported to be as high as 52% to 60%.^9–12 When evaluating an animal with otitis externa, it is important to determine the primary cause as well as any predisposing and perpetuating factors, so as to manage the otitis properly. Dermatological and neurological examinations should be performed, because concurrent dermatological disease is seen in 64% to 80% of cases,^2,3 and preoperative facial neuropathy occurs in approximately 15% of dogs with end-stage otitis.⁶ A thorough otoscopic examination (video or handheld) should also be performed on every animal with otitis externa.¹³ Both ears should be examined even if only a unilateral otitis externa is suspected.¹³

Para-aural swelling and fistulation can occur secondary to ear canal stenosis; these conditions are most commonly caused by hyperplastic proliferation in chronically diseased ears.⁴ Otitis media, foreign body migration, traumatic ear canal separation, diseases involving the parotid gland or the dental arcade, and osteomyelitis of the petrous temporal bone constitute other causes of fistulation.^14,15 Fistulae also develop in 3% to 15% of dogs treated for chronic otitis by TECA and either lateral or ventral bulla osteotomy.^2,3,6,15,16

Either video or handheld otoscopy can be used for the diagnosis of ear diseases in small animals; however, video otoscopy has several advantages over the handheld otoscope. Video otoscopy provides a high degree of magnification, allowing greater visualization and detailed resolution of the ear canal and tympanic membrane. Compared to handheld otoscopy, some disadvantages of video otoscopy are that the animal must be anesthetized and placed in lateral recumbency; saline is needed for visualization; and more equipment and staff are required for the procedure to be performed.¹³ Diagnostic imaging techniques (i.e., conventional radiography, computed tomography [CT], and MRI) can become useful when otoscopy is impossible or nondiagnostic; when complete assessment of the tissues surrounding the ear canal is needed; or when the middle ear needs evaluation.^17–19 Radiography is commonly used but often lacks sensitivity.^17–21

Cross-sectional imaging techniques are complementary imaging techniques that are used in referral, not general, practices to assess the contents of and pathological changes affecting the external ear canal, the middle ear, labyrinth, and internal auditory canal.^20,21 Fistulography may be useful to define fistula length, location, and origin.¹⁴ Although ultrasonography has been reported to evaluate the tympanic bulla and ear canals, it has several limitations compared to other imaging modalities and is not recommended as a replacement for radiography, CT, or MRI.¹⁹

In the case presented here, ultrasound was a useful adjunct to evaluate the subauricular mass, and it allowed us to obtain cytological information. Computed tomography provides excellent cross-sectional images of the ear canal, tympanic bulla, and internal ear; superimposition is eliminated, and image contrast is superior to that provided by conventional radiography.^7,21 Magnetic resonance imaging also eliminates superimposition and is superior for imaging soft tissue components. As illustrated in this case, MRI also provides specific information on tissue composition through various imaging sequences.²¹ For example, the fat-suppression images showed attenuation of the cyst material, indicating the soft tissue mass had a fatty component that was consistent with cerumen or sebaceous material. In complex cases such as the one reported herein, more than one imaging technique may be required for diagnosis.

Ear canal masses or mass-like lesions have previously been reported in dogs and include abscessation, ceruminous gland hyperplasia, and benign or malignant tumors.^22,23 Ear canal tumors in dogs and cats are relatively uncommon, representing only 1% to 2% of all tumors in cats^24,25 and 2% to 6% of all tumors in dogs admitted for aural surgery.^26,27 Ear canal tumors tend to be more aggressive in cats than in dogs.²³ The most commonly reported aural tumors affecting dogs include ceruminous gland adenoma and adenocarcinoma, papilloma, and histiocytoma.^25–27 In the cat, ceruminous gland adenoma and adenocarcinoma are also common, and, unlike dogs, cats are more frequently diagnosed with inflammatory polyps involving the middle ear and squamous cell carcinoma of the pinnae.²³

To our knowledge, multiple follicular cysts have never been reported in the ear canals of dogs or cats. In humans, epidermal cysts occur most commonly on the face, scalp, neck, and trunk; for epidermal (follicular) cysts to appear in the external auditory canal is extremely rare.²⁸ Only two human cases of epidermal (follicular) cysts of the external auditory canal appear to have been reported to date.^29,30 In dogs and cats, follicular cysts are considered benign skin lesions that can be surgically removed and have no tendency to recur.³¹

Follicular cysts, epidermoid cysts, epidermal inclusion cysts, epidermal cysts, and infundibular cysts yield a similar cytological pattern. They appear as cysts lined by stratified squamous epithelium containing predominantly mature, keratin-producing, squamous epithelial cells. They are filled with amorphous, basophilic cellular debris.³² Keratin bars, squames, or other keratinocytes predominate on cytology. Clear, notched, rectangular cholesterol crystals resulting from cellular breakdown may be present.^31,32 If the cysts have ruptured, a typical cellular inflammatory reaction with populations of neutrophils and macrophages may be present within the background basophilic cellular debris.³¹ On histology, the keratinized cells that line the cyst are loosely packed or tightly compressed.³² All four layers of the normal epidermis or infundibulum, including the granular cell layer, are present. Lesions can be solitary or multiple, but usually they are unilocular.³¹ By definition, the lack of adnexal differentiation without a connection to the skin surface seen histologically is considered an epidermal inclusion cyst.³¹ The more common follicular cyst is characterized by a distended hair follicle infundibulum that opens to the surface via a pore. This distinction cannot be made cytologically.¹

In humans, the epidermal cyst wall must be completely removed, because residual portions of the cyst will result in recurrence. In this case, we recommended surgery as soon as possible, because the cyst was close to the middle ear. If the cyst had ruptured or become infected, the middle ear involvement might have worsened and negatively impacted the dog’s prognosis.³⁰

For dogs and cats with end-stage otitis externa or masses confined to the ear canal, TECA-LBO is widely accepted as a viable treatment option.^3–6,16 However, variable results and complication rates have been reported.^2–5 The goal of TECA-LBO is to remove all of the diseased ear canal and middle ear tissues, provide drainage of the surgical site, and promote healing in a way that minimizes potential infectious or other inflammatory complications. Performance of TECA-LBO is elected when other treatments fail to resolve otitis externa or when irreversible ear canal disease is present. Such irreversible diseases include hyperplastic epithelium or neoplasia occluding the lumen of the horizontal ear canal, collapse/stenosis of the horizontal canal caused by infection, and calcified periauricular tissues.² Aural trauma and obstructive congenital malformations are also indications for surgical intervention.^14,27,33,34

In the TECA-LBO preoperative period, it is important to determine any preexisting complications and to ensure that the owner has a firm understanding of the possible treatment-related complications associated with this procedure.^2–5 Facial nerve deficits, as seen in this case, are common.^2–5 The facial nerve or branches of the facial nerve can be damaged during dissection or tissue retraction. Clinical signs include a slow or absent palpebral reflex and hemifacial paresis leading to drooping of the ipsilateral eye and lip margins.^4,14,33 With proper treatment, this complication is often temporary and free of long-term sequelae.^2–5 In 10% to 15% of cases, facial nerve damage is permanent; however, long-term artificial tear application is not necessary, because continued lacrimal function, passive movement of the third eyelid (controlled by cranial nerve VI), and abducens nerve-mediated globe retraction are sufficient to ensure a proper corneal tear film.^3,4

Conclusion

Multiple follicular cysts with otitis media and externa were diagnosed and evaluated in a dog with the aid of ultrasound, MRI, cytology, and histopathology. Surgical treatment was curative and associated with only minor complications. Based on the results of this report, TECA-LBO appears to be a viable treatment for otitis externa and media associated with multiple follicular cysts of the external ear canal.

Acknowledgments

The authors thank Dr. Michel Desnoyer and Dr. Manon Paradis for their clinical expertise; Dr. Pierre Hélie for providing the histopathological images; and Mr. Richard Bourassa for image editing.