Segmental mandibulectomy as a novel adjunct management strategy for the treatment of an advanced cholesteatoma in a dog

Abstract

A 6-year-old spayed female Labrador retriever dog was evaluated for trismus and peripheral vestibular syndrome. Computed tomography (CT) revealed a mass arising from the tympanic bulla consistent with a cholesteatoma. A total ear canal ablation, bulla osteotomy, and adjunct segmental mandibulectomy were performed. Re-evaluation 2 weeks after surgery revealed no neurologic abnormalities, normal jaw range of motion, and no discomfort. Despite concern for recurrence of cholesteatoma based on CT imaging performed 33 months after surgery, repeat surgical intervention was not pursued as the owner considered the dog’s comfort level to be satisfactory. The patient continued to do well for the 42-month follow-up period.

Aural cholesteatoma is an uncommon condition of dogs resulting from the formation of an epidermoid cyst in the middle ear cavity that is characterized by destructive and expanding keratinizing stratified squamous epithelium (1–5). Cholesteatomas can be a severe complication of chronic otitis in both dogs and humans for which surgical treatment is usually necessary (1,2,4). Surgical approaches include ventral bulla osteotomy, total ear canal ablation, and lateral bulla osteotomy (TECA-LBO), a caudal auricular approach and an intra-oral approach (1,6,7). The goal of surgical management is to meticulously remove all keratin debris and stratified squamous epithelium. Failure to do so is thought to significantly contribute to a high rate of recurrence, reported in approximately 50% of cases (1,5). In humans, the gold standard for cholesteatoma management utilizes microscopic- or endoscopic-assisted surgical techniques to improve middle ear visualization and minimize the risk of leaving behind residual disease (8).

Surgical treatment for cholesteatoma can be curative, most often in cases that are detected early when lesions are small. Hardie et al (1) reported a high recurrence rate and worse median survival time (MST) for patients with advanced cholesteatomas that resulted in an inability to open the mouth and/or neurologic signs. These dogs had a short MST of 16 mo compared with cases in which the only clinical sign was chronic otitis externa and the MST could not be calculated, as > 50% of dogs were still alive at last contact (1). Despite this observation, strategies to address disease recurrence are lacking. In humans with extensive disease in which residual disease is uncertain, second look, and second stage procedures are planned (9). This article describes a potential surgical option that may serve to palliate clinical signs and prolong the interval of time before a second surgical intervention is necessary, in cases of advanced cholesteatomas.

Management of an advanced cholesteatoma with primary surgical excision and adjunctive segmental mandibulectomy has not previously been described in the veterinary literature. The report herein highlights the long-term outcome following a TECA-LBO and segmental mandibulectomy for the treatment of an advanced cholesteatoma causing trismus and neurologic signs in a dog.

Case description

A 6-year-old spayed female Labrador retriever dog was presented for surgical treatment of an advanced cholesteatoma. The dog had a longstanding history of chronic otitis externa, a 10-month history of head and neck sensitivity, reluctance to retrieve toys, and difficulty prehending food. For 7 mo before presentation, the patient had been treated for presumed masticatory muscle myositis, as clinical signs were initially steroid-responsive. Over that period, an initial 1 mg/kg body weight (BW) oral dose of prednisone (West-Ward Pharmaceutical, Eatontown, New Jersey, USA) once daily had been tapered to a lowest effective dose of 0.25 mg/kg BW orally once daily. Subsequent development of a left-sided head tilt prompted referral of the patient.

A month prior to surgical consultation, the dog was presented to the neurology service for left-sided peripheral vestibular syndrome, characterized by a 15-degree left-sided head tilt. On examination, moderate bilateral temporal and masticatory muscle atrophy was detected and the patient experienced pain upon opening the mouth. The rest of the patient’s general physical and neurologic examination was unremarkable. Differential diagnoses for the patient’s clinical signs included inflammatory diseases (e.g., immune-mediated masticatory muscle myositis, otitis media), neoplasia, temporomandibular joint disease, hypothyroidism, and infectious diseases. Advanced imaging of the skull and full blood analysis were pursued to further localize a source of the dog’s clinical signs. The patient was sedated with butorphanol (Torbugesic; Zoetis, Parsippany, New Jersey, USA), 0.2 mg/kg BW, IV, and dexmedetomidine (Dexdomitor; Zoetis), 15 μg/kg BW, IV, for a computed tomography (CT) scan of the skull. Imaging revealed an abnormal left tympanic bulla with marked expansion and sclerosis of the osseous wall. Periosteal reaction and lysis were evident in the walls of the bulla. The margins of proliferative bone extended to the caudal ventral portion of the zygomatic arch and mandibular fossa. A proliferative mass with peripheral contrast enhancement within the left tympanic bulla extended into the horizontal ear canal (Figures 1A, B). Computed tomography characteristics of the mass including tympanic bulla expansion and “ring” (i.e., peripheral, not diffuse) contrast enhancement suggested a slow growing cholesteatoma versus middle ear neoplasia (5). To obtain a definitive diagnosis and help with prognostication, video-otoscopy with the plan to biopsy the mass was attempted but was unsuccessful due to profound stenosis of the horizontal ear canal. A complete blood (cell) count (CBC), serum biochemistry panel, and total thyroxine (T4) test were carried out. The CBC demonstrated low lymphocytes [0.51 × 10³/μL, reference range (RR): 1.0 to 4.8 × 10³/μL] and eosinophils (0.0 × 10³/μL, RR: 0.1 to 1.0 × 10³/μL). Other blood abnormalities were consistent with long-term prednisone therapy including elevations in alkaline phosphatase (211 U/L, RR: 7 to 92 U/L), alanine aminotransferase (140 U/L, RR: 8 to 65 U/L), gamma-glutamyl transferase (11 U/L, RR: 0 to 7 U/L), cholesterol (8.8 mmol/L, RR: 3.3 to 7.7 mmol/L), and a low total T4 (< 6.44 nmol/L, RR: 15.0 to 48.0 nmol/L). The patient was subsequently referred to the surgery service for further treatment.

Figure 1.

Preoperative computed tomography images. A — Post-contrast, soft-tissue algorithm, transverse image at the level of both tympanic bullae. A soft tissue mass fills the left tympanic cavity, causing marked expansion, sclerosis and osteoproliferation of the osseous wall. B — Transverse image at the level of the temporomandibular joint (TMJ). The cranial extension of the left tympanic bulla and its intimate association with the TMJ are outlined with green arrows. Periarticular changes can be observed, including sclerosis of the mandibular fossa and condylar process.

On presentation for surgical consultation, the patient exhibited a left-sided head tilt, severe masticatory muscle atrophy bilaterally (worse on the left), left mandibular lymphadenopathy, and pain on manipulation of its mandibles. Other general physical features were unchanged from the previous examination. Preoperative staging diagnostics were performed. The patient was sedated with the same protocol described for the skull CT for an abdominal ultrasound and an ultrasound-guided fine-needle aspiration of the left tympanic bulla and left mandibular lymph node. Three-view thoracic radiographs and an abdominal ultrasound showed no evidence of metastatic disease. Fine-needle aspiration and cytologic assessment of the left tympanic bulla yielded a non-diagnostic sample, and the left mandibular lymph node was consistent with inflammation (no evidence of neoplastic cells was discovered). Due to the patient’s history of chronic otitis, lack of cytologic diagnosis, and appearance on CT (5), a high index of suspicion was given to a cholesteatoma, although aural neoplasia could not be ruled out.

For both diagnostic and therapeutic purposes, a left-sided TECA-LBO was recommended. Although it was anticipated that a TECA-LBO alone would provide immediate relief of clinical signs, due to the advanced nature of the lesion [supported by the marked expansive boney remodeling of the bulla that demonstrated encroachment of the temporal mandibular joint (TMJ) (Figure 1B)] and the clinical signs of trismus and neurologic deficits, the prognosis for regression of the lesion and long-term resolution of clinical disease was poor. An adjunctive left-sided segmental mandibulectomy was suggested in an attempt to improve quality of life for the patient in both the near-term and the long-term. The short-term aim was to release the left mandible and off-load the left TMJ. This would indirectly address any conflict or impingement of the tympanic bulla with the TMJ that may have been contributing to the clinical signs of pain and difficulty on opening of the mouth. The long-term consideration was to reduce the probability of a second procedure being necessary if local disease recurred.

The patient was premedicated with methadone (Methadone Hydrochloride; Bioniche Pharma, Lake Forest, Illinois, USA), 0.25 mg/kg BW, IM, and dexmedetomidine (Dexdomitor; Zoetis), 3 μg/kg BW, IM. Anesthesia was induced with alfaxalone (Alfaxan Multidose; Jurox, North Kansas City, Missouri, USA), 1.75 mg/kg BW, IV, and maintained with an isoflurane (Isoflo; Abbott Labs, North Chicago, Illinois, USA) oxygen mix via endo-tracheal tube. Prior to surgery, local auricular and inferior alveolar nerve blocks were performed by infiltrating each nerve with bupi-vacaine (Marcaine; Hospira, Lake Forest, Illinois, USA), 1 mg/kg BW, distributed between both locations. Ampicillin (Ampicillin Sodium; Sandoz, Princeton, New Jersey, USA) was administered during surgery (22 mg/kg BW, IV every 90 min). A continuous rate infusion (CRI) of ketamine (Ketaset; Zoetis), 5 μg/kg BW per min, IV, fentanyl (Fentanyl Citrate; Hospira), 5 μg/kg BW per min, IV, and lidocaine (Lidocaine Hydrochloride; Hospira), 30 μg/kg BW per minute, IV, were administered throughout the surgical procedure. A left-sided TECA-LBO was performed, as previously described (10). The vertical and horizontal ear canals appeared grossly normal from the exterior. The bulla was diffusely distended and contained copious amounts of tan-to-white, thick, spongy material that readily exfoliated. No mass-like lesion was observed during surgery. The walls of the bulla were dense, thickened, and proliferative. Material from the bulla was collected and submitted for aerobic and anaerobic bacterial culture and histopathology. As an adjunct procedure, a left-sided segmental mandibulectomy was performed, as previously described (11). The mandibulectomy excision spanned from the mesial aspect of the fourth premolar tooth (307) to the distal aspect of the first molar tooth (310) (Figure 2B).

Figure 2.

Recheck computed tomography (CT) images. A — Post-contrast, soft-tissue algorithm, transverse image through both tympanic bullae demonstrating recurrence of the soft tissue mass. The left ear canal is absent (consistent with previous TECA-LBO). B — Ventral view of a three-dimensional (3-D) CT reconstruction showing the segmental mandibulectomy (green arrows), and subsequent medial displacement of the right mandible. The segmental mandibulectomy included excision of the left fourth premolar and first molar. C, D — Left and right sagittal views of a 3-D CT reconstruction demonstrating recurrence of the soft tissue mass and continued impingement on the temporo-mandibular joint (TMJ) on the left side compared to the unaffected right side. The green arrows delineate the extent of the bulla on each side.

The patient recovered uneventfully from anesthesia and remained hospitalized for supportive care. After surgery, the same analgesic protocol administered during surgery was continued, with the exception that the fentanyl CRI was switched to a morphine CRI (Morphine Sulfate; West Ward Pharmaceutical), 0.1 mg/kg BW per hour, IV. Two additional doses of ampicillin (22 mg/kg BW, IV, q8h) were given, and then antimicrobial therapy was discontinued. After 24 h, IV analgesics were discontinued, and the patient was transitioned to tramadol (Janssen Pharmaceuticals, Titusville, New Jersey, USA), 5 mg/kg BW, PO, q8h, gabapentin (TEVA pharmaceuticals USA, Sellersville, Pennsylvania, USA), 5 mg/kg BW, PO, q8h and restarted on prednisone (West-Ward Pharmaceutical), 0.25 mg/kg BW, PO, q24h. The patient was comfortable and eating well 36 h after surgery. The dog was discharged from the hospital 48 h after surgery with 2 wk of tramadol, gabapentin, and a tapering course of prednisone.

Histopathology showed that the submitted tissue from the left bulla was composed entirely of large sheets of keratin debris, consistent with a cholesteatoma. Both aerobic and anaerobic cultures recovered no bacterial growth.

On re-evaluation 2 wk after surgery, the surgical incisions were healed. The patient had been eating well with no issues reported by the owner. No neurologic abnormalities were noted on examination, and compared to prior oral examinations, the patient showed improved comfort. The dog allowed full opening of the mouth and was comfortable during evaluation of the oral cavity. Medial deviation of the mandibles and malocclusion was observed, but no clinical signs or evidence of traumatic palatal or gingival lesions were present at that time. Prednisone therapy was weaned and discontinued 21 d after surgery.

The dog was assessed at 33 mo after surgery by the dentistry service for reluctance to prehend food for the previous week and halitosis of 2 months’ duration. On physical examination, the patient had persistent atrophy of the temporalis and masseter muscles bilaterally (worse on the left) and left displacement of both mandibles relative to the maxilla. The patient was comfortable on external palpation of her muzzle and head but evaded oral examination and assessment of mandibular range of motion could not be performed while the patient was awake. No neurologic abnormalities were noted. After sedation, the dog’s mouth could be fully opened without interference or crepitus. When manual pressure was applied to the left mandibular segment caudal to the mandibulectomy site, minimal movement (~1 to 2 mm) in only the ventral direction could be elicited. Other abnormalities reported included traumatic occlusion of the right mandibular canine with the palate, traumatic occlusion of the left maxillary canine with the left mandibular second incisor, third incisor, and canine, as well as severe erosion with pulp exposure of the left maxillary second molar from contact with the left mandibular second molar. A CT scan demonstrated marked expansion of the left tympanic bulla with a heterogeneously attenuating soft tissue mass (Figures 2A, C, D), previous left segmental mandibulectomy with secondary mandibular displacement and malocclusion (Figure 2B), mild enlargement of the left medial retropharyngeal and left mandibular lymph nodes as well as mild right otitis externa. Although concern for recurrence of the cholesteatoma was discussed with the owner, correction of the dental abnormalities was pursued, and the owner elected to consider a second surgery only if clinical signs did not improve with dental work alone. Crown reduction, vital pulpotomy, and direct capping of the affected canine teeth as well as extraction of several teeth readily restored the patient’s appetite the following day.

After the initial surgery, the patient showed no interest in hard kibble, but readily ate softened kibble or canned food. Approximately 36 mo after surgery, the owners began blending the dog’s food to a gruel consistency as they reported lack of interest in softened kibble but good appetite with blended food.

A telephone interview was conducted 42 mo following surgery. In the time since surgery, the primary care veterinarian had started the dog on a daily non-steroidal anti-inflammatory drug for osteoarthritis. The owner reported a good quality of life, with no signs of pain or discomfort. The patient continued to be able to open her mouth, but the extent of this was not described in detail by the owner.

Discussion

The case presented herein describes the use of an adjunctive procedure for treatment of an advanced cholesteatoma. In conjunction with a TECA-LBO, a segmental mandibulectomy may offer benefit in treating patients with advanced disease in which the expanding lesion may cause impingement of the mandible, resulting in pain or mechanical difficulty in opening the mouth. These cases have a poor prognosis and high recurrence rate, making it challenging to achieve durable lesion regression with a TECA-LBO alone (1).

The most common findings in dogs with aural cholesteatomas include a history of chronic otitis, ear pain, pain on TMJ palpation, and discomfort when opening the mouth. Neurologic signs such as facial palsy, head tilt, and ataxia can also occur (4). Cases with advanced disease more frequently present with neurologic signs and/or inability to open the mouth (1). The time elapsed between development of clinical signs and surgical treatment is an important consideration when making treatment decisions. In cases in which the diagnosis is made early in the course of disease, surgical intervention can be curative. A bulla osteotomy via any of the approaches previously mentioned may palliate clinical signs of advanced cholesteatomas by restoring comfort during mastication and resolving neurologic signs (1,4–6). However, the duration of relief, median survival, and likelihood of a single-episode surgery being curative are all less in advanced cases due to the chance of recurrence being higher (1).

The authors’ goals in performing a segmental mandibulectomy as an adjunct strategy in this case were two-fold. The first was to alleviate any component of the patient’s clinical signs that were due to dynamic impingement of the TMJ created by the mass effect from the expansive cholesteatoma and collateral inflammation, and the second was to maintain quality of life and extend the duration of time before a repeat surgical intervention was necessary. The idea behind this intervention was that a segmental mandibulectomy releases the relationship between the caudal portion of the mandible, which is in proximity to the diseased bulla, from the remaining mandible in order to preserve contralateral jaw function and minimize discomfort during mastication long-term. In an experimental study in dogs in which unilateral rostral mandibulectomy was performed, microscopic evidence of accelerated articular wear was observed within the TMJ ipsilateral to the intact mandible compared to the TMJ associated with the resected mandible (12). In addition, resorption of the mandibular condyle on the operated mandible was more substantial compared to that on the intact side (12). The findings from this study illustrate how partial mandibulectomy can result in “loading” of the TMJ on the side of the intact mandible and “unloading” of the TMJ on the side of the resected mandible (12), which was the ultimate goal of performing a segmental mandibulectomy in this case.

Although a caudal mandibulectomy may have been a viable alternative strategy to a segmental mandibulectomy, it was not selected. The authors felt that the dissection necessary to perform a caudal mandibulectomy and concurrent TECA-LBO would have been more extensive than for a segmental mandibulectomy with respect to total surgical and anesthetic duration and postoperative recovery. A caudal mandibulectomy would have involved transection or elevation of most soft tissue structures that extend from the skull to the mandible and depending on the exposure available from an intraoral approach, a zygomatic arch osteotomy may have been necessary (13). A segmental mandibulectomy performed rostral to the insertion of the digastric muscle involved no transection or elevation of muscle and added minimal surgical time. Furthermore, distortion of the normal anatomic course of the major neurovascular structures (including the maxillary artery and its local branches) secondary to the expansile cholesteatoma may have resulted in an increased risk of inadvertent injury or transection of these structures had a caudal mandibulectomy been performed. Performing a segmental mandibulectomy circumvented this issue.

The location for the segmental mandibulectomy was selected so that rostral dentition on the ipsilateral side would remain, thereby maximizing the occlusal surface of the residual mandible for mastication. The length of mandibulectomy was chosen to create a critical defect that would span a distance across which healing would not occur, in order to avoid recurrence of clinical signs.

Application of segmental mandibulectomy as an adjunct management strategy provided both early and long-term relief of this patient’s clinical signs and maintained good quality of life. The potential for mandibular drift and anticipated complications associated with secondary traumatic malocclusion should be noted. In hindsight, intentional crown reduction with vital pulp therapy or tooth extraction of the contralateral mandibular canine may have been performed at the time of segmental mandibulectomy as a preventative measure to avoid palatal trauma. Alternatively, an elastic training technique that involved the use of orthodontic buttons and power chain extending from the canine tooth of the intact mandible to the ipsilateral fourth maxillary premolar to prevent mandibular drift could have been performed (14). To improve outcome and lessen signs of mandibular drift, owners should be encouraged to provide their pets with access to larger kibble, and soft and hard toys as part of the physiotherapeutic treatment.

Lastly, it should be noted that subjectivity exists in how assessment of the patient’s comfort was reported. We have to rely on owner interpretation of their pet’s behavior while also being mindful of an individual’s subjective level of tolerance for these observations. This should be reflected in the follow-up telephone call assessment, for which the owner, despite knowledge of disease recurrence detected on the follow-up CT imaging, perceived this patient’s overall comfort to be well-managed on chronic non-steroidal anti-inflammatory therapy. Additional clinical investigations are warranted to investigate whether this management strategy is associated with a meaningful improvement in patient outcome for a larger population of animals. CVJ