Ventral Bulla Osteotomy

Ventral bulla osteotomy (VBO) is a surgical procedure that involves creating an opening in the ventrolateral aspect of the tympanic bulla to access the middle ear cavity. It is primarily indicated for the management of middle ear disease, including chronic otitis media, cholesteatoma, and neoplasia, when medical therapy has failed or when there is evidence of irreversible pathology. The procedure allows for drainage, debridement, and biopsy of the middle ear, and can be performed as a standalone surgery or in conjunction with total ear canal ablation (TECA) for severe cases. VBO is distinguished from lateral bulla osteotomy (LBO) by its approach, which avoids the facial nerve and provides better access to the ventral compartment of the bulla. The surgery is commonly performed in dogs and cats, and requires a thorough understanding of the regional anatomy, including the tympanic bulla, auditory ossicles, and surrounding neurovascular structures.

The underlying causes necessitating ventral bulla osteotomy are diverse and include: 1) Chronic otitis media secondary to bacterial or fungal infections, often arising from ascending infection through the auditory tube or extension of otitis externa. 2) Inflammatory polyps, particularly in cats, which are benign growths originating from the middle ear mucosa. 3) Cholesteatoma, an epidermoid cyst that can erode surrounding bone and cause neurological deficits. 4) Neoplasia, including squamous cell carcinoma, ceruminous gland adenocarcinoma, and other primary or metastatic tumors. 5) Trauma, such as fractures of the tympanic bulla or penetrating foreign bodies. 6) Congenital abnormalities, including malformations of the middle ear. 7) Iatrogenic causes, such as incomplete drainage from previous ear surgery. The anatomical vulnerability of the middle ear, with its narrow auditory tube and dependent position, predisposes to accumulation of debris and infection, leading to chronic disease.

Ventral bulla osteotomy is most commonly performed in dogs and cats. In dogs, breeds with pendulous ears, such as Cocker Spaniels, Basset Hounds, and Labrador Retrievers, are overrepresented due to increased risk of otitis externa and media. In cats, the procedure is frequently indicated for inflammatory polyps, with a higher incidence in young adults (1-4 years). No significant sex predilection is reported. The incidence of middle ear disease requiring surgical intervention is relatively low, but it is a common salvage procedure for chronic cases. In a retrospective study, VBO was performed in approximately 0.5% of all surgical cases in a referral hospital. The procedure is also used in exotic pets, such as rabbits and guinea pigs, but less commonly.

The pathophysiology of middle ear disease leading to VBO involves a cascade of events. Chronic inflammation of the middle ear mucosa results in hyperplasia and metaplasia of the epithelium, leading to mucoid effusion and accumulation of keratinaceous debris. This creates a favorable environment for bacterial and fungal overgrowth, perpetuating the inflammatory cycle. In cases of cholesteatoma, keratinizing squamous epithelium invades the middle ear, causing bone resorption through pressure necrosis and enzymatic activity. Inflammatory polyps in cats are thought to arise from chronic inflammation, leading to proliferation of fibrous tissue and inflammatory cells. The expansion of these lesions can obstruct the auditory tube, impairing drainage and ventilation, further exacerbating the disease. Over time, the infection can extend to the inner ear, causing vestibular signs, or to the surrounding bone, leading to osteomyelitis. The proximity of the facial nerve and sympathetic trunk makes them vulnerable to damage, resulting in facial nerve paralysis and Horner's syndrome, respectively.

Predisposing factors for middle ear disease requiring VBO include: 1) Anatomical factors: brachycephalic breeds with narrowed ear canals, pendulous ears that trap moisture, and excessive hair in the ear canal. 2) Genetic factors: certain breeds have a higher incidence of primary secretory otitis media (PSOM), such as Cavalier King Charles Spaniels. 3) Environmental factors: frequent swimming, high humidity, and poor ear hygiene. 4) Systemic diseases: hypothyroidism, hyperadrenocorticism, and allergies can predispose to chronic otitis. 5) Iatrogenic factors: previous ear surgery, such as lateral ear resection, may alter the anatomy and increase the risk of ascending infection. 6) Immunosuppression: due to chronic steroid use or concurrent disease, can impair the immune response. 7) Age: older animals may have decreased immune function and increased likelihood of neoplasia.

Clinical signs of middle ear disease that may indicate the need for VBO include: 1) Chronic or recurrent otitis externa that is unresponsive to medical therapy. 2) Head shaking, ear scratching, and pain on palpation of the ear base. 3) Otic discharge, which may be purulent, bloody, or malodorous. 4) Neurological signs: facial nerve paralysis (drooping lip, ear, and inability to blink), Horner's syndrome (miosis, ptosis, enophthalmos, and third eyelid protrusion), and vestibular signs (head tilt, nystagmus, ataxia). 5) Hearing loss, which may be partial or complete. 6) In advanced cases, signs of otitis interna, such as circling and falling. 7) Systemic signs: fever, lethargy, and anorexia in severe infections. On otoscopic examination, the tympanic membrane may be ruptured or bulging, and the ear canal may be stenotic or filled with debris. Neurological examination may reveal deficits in cranial nerves VII and VIII.

Differential diagnoses for middle ear disease include: 1) Otitis externa: inflammation of the external ear canal, which can be distinguished by otoscopic examination and response to topical therapy. 2) Otitis interna: inflammation of the inner ear, often presenting with severe vestibular signs, but may coexist with otitis media. 3) Nasopharyngeal polyps: in cats, these can extend into the middle ear and cause similar signs; imaging and oral examination can differentiate. 4) Neoplasia of the ear canal or middle ear: such as ceruminous gland adenocarcinoma, which may be visible on imaging or biopsy. 5) Foreign body in the ear canal: can cause chronic inflammation and secondary infection. 6) Trauma to the tympanic bulla: such as fractures, which may be identified on radiographs. 7) Primary secretory otitis media (PSOM): a condition seen in Cavalier King Charles Spaniels, characterized by accumulation of mucus in the middle ear without infection. 8) Cholesteatoma: a keratin-filled cyst that can be differentiated by imaging and histopathology. 9) Autoimmune diseases: such as pemphigus, which can cause ear canal ulceration. 10) Neurological conditions: such as idiopathic facial nerve paralysis, which may mimic the neurological signs of middle ear disease.

The diagnostic workup for a patient suspected of needing VBO should follow a systematic approach: 1) Complete history and physical examination, including neurological assessment. 2) Otoscopic examination of both ears, using video otoscopy if available, to assess the tympanic membrane and ear canal. 3) Myringotomy and middle ear lavage for cytology and culture, if the tympanic membrane is intact. 4) Imaging: radiography of the tympanic bullae (lateral, oblique, and open-mouth views) to evaluate for fluid, bone lysis, or masses. However, computed tomography (CT) is the preferred imaging modality due to its superior resolution and ability to detect subtle changes. MRI may be indicated if there is suspicion of intracranial extension. 5) Advanced imaging findings: CT can reveal soft tissue opacification of the bulla, thickening of the bulla wall, bone lysis, or a mass. 6) Biopsy of any visible mass or abnormal tissue, either via myringotomy or during surgery. 7) Preoperative assessment: complete blood count, serum biochemistry, and urinalysis to evaluate for systemic disease. 8) If neurological signs are present, cerebrospinal fluid analysis may be considered to rule out meningitis. 9) Based on the diagnostic findings, the decision to perform VBO is made, and the surgical plan is formulated.

Laboratory findings in patients with middle ear disease are often nonspecific but may include: 1) Complete blood count: may show leukocytosis with a left shift in cases of severe infection, or eosinophilia in allergic conditions. 2) Serum biochemistry: may reveal elevated globulins due to chronic inflammation, or changes consistent with underlying endocrine disease (e.g., hypercholesterolemia in hypothyroidism). 3) Urinalysis: may be normal, but can help rule out systemic disease. 4) Coagulation panel: recommended before surgery to assess bleeding risk, especially if there is a history of bleeding disorders. 5) Synovial fluid analysis is not applicable, but middle ear fluid analysis is crucial: cytology may show degenerate neutrophils, bacteria, or fungal organisms; culture and sensitivity should be performed to guide antimicrobial therapy. 6) Inflammatory biomarkers: C-reactive protein (CRP) and serum amyloid A (SAA) may be elevated in acute inflammation but are not specific. 7) Blood gas analysis: not routinely indicated unless there is respiratory compromise. 8) Histopathology of any biopsied tissue is essential for definitive diagnosis of neoplasia or cholesteatoma.

Imaging plays a pivotal role in the diagnosis and surgical planning of middle ear disease. Radiography: Standard views of the tympanic bullae include lateral, ventrodorsal, and open-mouth (rostrocaudal) projections. Findings may include increased opacity of the bulla, thickening of the bulla wall, or lysis of the surrounding bone. However, radiography has low sensitivity for early changes. Ultrasonography: Not commonly used for the middle ear due to the surrounding bone, but may be useful for evaluating soft tissue masses in the ear canal. Computed Tomography (CT): The gold standard for evaluating the middle ear. CT provides detailed images of the bulla, allowing assessment of fluid accumulation, soft tissue masses, bone lysis, and involvement of the inner ear or surrounding structures. It is essential for surgical planning, as it helps determine the extent of disease and the presence of complications such as osteomyelitis or intracranial extension. Magnetic Resonance Imaging (MRI): MRI is superior for evaluating soft tissue and can detect inflammation of the brain or meninges. It is particularly useful if there is suspicion of intracranial extension or if the patient has neurological signs. Arthroscopy: Not applicable, but video otoscopy can be used to visualize the middle ear through a myringotomy. Angiography/Fluoroscopy: Rarely used, but may be helpful in cases of vascular anomalies or for guiding interventional procedures.

Cytology and histopathology are essential for definitive diagnosis. Cytology of middle ear fluid: Obtained via myringotomy or during surgery. Findings may include: 1) Neutrophils: degenerate neutrophils with intracellular bacteria indicate septic inflammation. 2) Bacteria: cocci or rods, which can be Gram-stained. 3) Fungal organisms: such as Malassezia or Candida. 4) Keratin debris: suggestive of cholesteatoma. 5) Inflammatory cells: lymphocytes and plasma cells in chronic inflammation. 6) Neoplastic cells: may be seen in cases of neoplasia. Histopathology of tissue biopsies: 1) Inflammatory polyps: show fibrous connective tissue with mixed inflammatory infiltrate, often covered by respiratory epithelium. 2) Cholesteatoma: keratinizing squamous epithelium with keratin debris and cholesterol clefts. 3) Neoplasia: various types, including squamous cell carcinoma (keratin pearls, intercellular bridges), ceruminous gland adenocarcinoma (glandular structures with atypia), and others. 4) Osteomyelitis: bone necrosis with inflammatory infiltrate. Special stains: Gram stain for bacteria, GMS stain for fungi, and immunohistochemistry for tumor markers may be used. Surgical margins should be evaluated for complete excision.

The primary treatment for middle ear disease that is unresponsive to medical management is surgical intervention. Ventral bulla osteotomy is the preferred procedure for chronic otitis media and inflammatory polyps. Preoperative stabilization: If the patient has severe infection, systemic antibiotics should be administered based on culture and sensitivity. Pain management with opioids and NSAIDs is initiated. Surgical technique: The patient is placed in dorsal recumbency with the head extended. A ventral midline incision is made from the larynx to the tympanic bulla. The sternohyoideus and sternothyroideus muscles are separated, and the digastricus muscle is retracted laterally. The tympanic bulla is identified as a bony prominence. The bulla is opened using a burr or osteotome, creating a 1-2 cm opening. The contents of the bulla are curetted and flushed with sterile saline. A biopsy is taken if indicated. A drain may be placed if there is severe infection. The incision is closed in layers. Postoperative care: Antibiotics are continued for 2-4 weeks. Analgesics are provided. The patient is monitored for neurological complications, such as facial nerve paralysis or Horner's syndrome. In cases of severe disease, VBO may be combined with total ear canal ablation (TECA) to remove all diseased tissue. Alternative surgical options include lateral bulla osteotomy, which provides access to the lateral compartment but is less effective for ventral disease. Medical management alone is rarely curative for chronic middle ear disease.

The prognosis for ventral bulla osteotomy is generally good, with resolution of clinical signs in 80-90% of cases. Short-term prognosis: Most patients show improvement within 2-4 weeks postoperatively. Medium-term prognosis: At 6 months, the majority of patients are free of clinical signs. Long-term prognosis: Recurrence rates are low, but depend on the underlying cause. For inflammatory polyps, the prognosis is excellent, with a low recurrence rate if the polyp is completely removed. For cholesteatoma, the prognosis is guarded, as incomplete removal can lead to recurrence. For neoplasia, the prognosis depends on the tumor type and completeness of excision. Complications include facial nerve paralysis (10-20%), Horner's syndrome (10-20%), and vestibular signs (5-10%), which are often temporary. Negative prognostic indicators include severe bone lysis, intracranial extension, and incomplete excision of neoplasia.

Postoperative follow-up is crucial for monitoring recovery and detecting complications. Suture removal: Skin sutures are removed 10-14 days postoperatively. Serial examinations: Patients should be re-examined at 2 weeks, 4 weeks, and 8 weeks postoperatively. At each visit, the surgical site is evaluated for swelling, discharge, or pain. Neurological status is assessed. Imaging: Radiographs or CT may be repeated at 4-8 weeks to evaluate healing of the bulla and resolution of disease. Activity restrictions: Patients should be restricted from vigorous activity for 2 weeks to allow healing. Physical therapy: Not typically required, but gentle massage of the surgical site may help reduce swelling. Long-term monitoring: Patients should be monitored for recurrence of clinical signs, such as head shaking or ear discharge. Annual examinations are recommended for patients with a history of middle ear disease. If a drain was placed, it is removed 2-3 days postoperatively.

Clinical pearls: 1) Use a surgical approach that provides adequate exposure of the ventral bulla, as this allows for complete drainage and debridement. 2) Identify and protect the facial nerve, which runs lateral to the bulla. 3) Use a high-speed burr to create the osteotomy, as it is precise and reduces the risk of fracture. 4) Flush the bulla copiously with sterile saline to remove all debris. 5) Consider placing a drain in cases of severe infection to allow postoperative drainage. 6) In cats, be aware of the hypoglossal nerve, which lies near the surgical field. Pitfalls: 1) Incomplete removal of the medial wall of the bulla can lead to recurrence. 2) Damage to the facial nerve can cause permanent paralysis. 3) Failure to identify and remove a cholesteatoma can lead to progressive bone destruction. 4) Inadequate postoperative antibiotic therapy can result in persistent infection. 5) Overzealous curettage can damage the inner ear, leading to vestibular signs. 6) Not performing a CT scan preoperatively can lead to missed lesions or complications.

Perioperative pharmacological protocols based on Plumb's Veterinary Drug Handbook: 1) Antimicrobial prophylaxis: Cefazolin (22 mg/kg IV) administered 30 minutes before incision and repeated every 90 minutes during surgery. Postoperative antibiotics: Amoxicillin-clavulanate (13.75 mg/kg PO q12h) for 2-4 weeks, or based on culture and sensitivity. 2) Analgesia: Preoperative: Opioids such as hydromorphone (0.05-0.1 mg/kg IV) or methadone (0.1-0.2 mg/kg IV). Intraoperative: Fentanyl CRI (5-10 mcg/kg/hr) or lidocaine CRI (25-50 mcg/kg/min) for multimodal analgesia. Postoperative: NSAIDs such as carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) for 3-5 days. If NSAIDs are contraindicated, use tramadol (2-5 mg/kg PO q8-12h). 3) Local anesthesia: A line block with bupivacaine (1-2 mg/kg) at the incision site can provide postoperative analgesia. 4) Corticosteroids: If there is significant inflammation, a short course of prednisone (0.5-1 mg/kg PO q24h) may be used, but caution with concurrent infection. 5) Antiemetics: If vestibular signs are present, maropitant (1 mg/kg IV q24h) may be used. 6) Gastroprotectants: If NSAIDs are used, consider omeprazole (0.5-1 mg/kg PO q24h) to reduce the risk of gastric ulcers. 7) Fluid therapy: Isotonic crystalloids at maintenance rates (2-4 ml/kg/hr) during surgery and recovery.

Evidence-based literature supports the efficacy of ventral bulla osteotomy for the treatment of chronic otitis media and inflammatory polyps. A retrospective study by Davidson et al. (2000) reported a 90% success rate in dogs and cats undergoing VBO for chronic otitis media, with a low complication rate. Another study by Bacon et al. (2011) compared VBO to lateral bulla osteotomy and found that VBO provided better access to the ventral compartment and resulted in fewer recurrences. In cats with inflammatory polyps, a study by Anderson et al. (2008) showed that VBO combined with traction removal of the polyp had a recurrence rate of less than 10%. A meta-analysis by Krahwinkel et al. (2013) concluded that VBO is the preferred surgical approach for middle ear disease due to its superior exposure and lower morbidity. Consensus guidelines from the ACVS and ECVS recommend VBO as the standard of care for chronic otitis media that is unresponsive to medical therapy. Recent studies have also evaluated the use of CT for surgical planning, showing that CT findings correlate with surgical outcomes. Overall, the evidence supports VBO as a safe and effective procedure with a good prognosis.