Surgical Diseases of the Upper Airway in Small Animals

Surgical Diseases of the Upper Airway

Overview of Upper Airway Anatomy and Function

• Upper Airway Components: Consists of the nares, nasal cavity, hard palate, soft palate, epiglottis, larynx, and trachea.

• Airflow: Air enters through the nose/nares, passes through the nasal cavity (or oral cavity), through the soft palate, epiglottis, larynx (voice box), and into the trachea (windpipe) during inhalation.

• Food/Water Passage: Food and water travel from the oral cavity, past the soft palate, epiglottis, to the esophagus (food pipe).

• Key Structures and Their Roles:- Nares: Nostrils, initial entry point for air.

  • Nasal Cavity: Warms, humidifies, and filters air.

  • Soft Palate: Separates the oral cavity from the nasopharynx; its length is crucial for normal breathing, especially in brachycephalic breeds.

  • Epiglottis: Flap of cartilage that covers the trachea during swallowing to prevent aspiration.

  • Larynx: Commonly called the voice box; vital for breathing, swallowing, and voice production. Contains vocal cords and arytenoid cartilages.

  • Trachea: Windpipe, carries air to and from the lungs.

  • Esophagus: Food tube, behind the trachea.

Diseases of the Nasal Cavity

• Anatomic:- Choanal atresia: Congenital malformation where the choana (posterior opening of the nasal cavity) fails to open, blocking the passage between the nasal cavity and the nasopharynx.

• Inflammatory:- Rhinitis/Sinusitis: Inflammation of the nasal lining and/or sinuses.

  • Nasopharyngeal stenosis: Narrowing of the nasopharynx, often due to inflammation or scarring.

• Infectious:- Aspergillosis (dogs): Fungal infection caused by Aspergillus species, leading to chronic nasal discharge and destruction of turbinates.

  • Cryptococcus (cats): Fungal infection, often presenting as a nasal granuloma or systemic disease.

  • Rhinosporidiosis: Chronic granulomatous disease caused by Rhinosporidium seeberi, affecting mucous membranes.

  • Nasal mites: Pneumonyssoides caninum, mites that infest the nasal passages and sinuses.

• Trauma: Injuries to the nasal area.

• Foreign Bodies: Objects lodged in the nasal cavity.

• Neoplasia (Tumors):- Common types: Adenocarcinoma, squamous cell carcinoma (SCC), lymphoma, mast cell tumors.

  • Implication: Often necessitates surgical intervention.

Nasal Diseases: History and Clinical Signs

• Nasal Discharge: Can be unilateral (one nostril) or bilateral (both nostrils); character (serous, mucoid, purulent, hemorrhagic) and duration are important.

• Sneezing: Reflex to clear nasal passages.

• Reverse Sneezing: Paroxysmal inspiratory effort, often associated with nasopharyngeal irritation.

• Stertor: Loud snoring or gasping sound, usually from nasopharyngeal or palatal obstruction.

• Epistaxis: Nosebleed.

• Facial Deformation: Swelling or asymmetry of the face, especially over the nasal bridge or sinuses.

• Ocular Discharge: Can be secondary to nasal blockage or inflammation affecting the nasolacrimal duct.

Differentials for Nasal Disease

• Dental Disease: Root abscesses or periodontal disease can erode into the nasal cavity or sinuses, causing nasal signs.

• Nasopharyngeal Polyp: Benign growths typically originating from the middle ear or Eustachian tube, extending into the nasopharynx or external ear canal.

Nasal Disease: Diagnostics

• Minimum Database:- CBC (Complete Blood Count): To assess for inflammation, infection, anemia.

  • Serum Chemistry: To evaluate organ function, systemic health.

• Sedated Oral Exam: Important to rule out oral causes of nasal signs and inspect the soft palate.

• Imaging:- Skull or Dental Radiographs: Limited utility for soft tissue, but can show bony changes, dental disease, or fluid accumulation in sinuses.

  • Thoracic Radiographs: To assess for concurrent respiratory disease, metastasis (in cases of neoplasia), or aspiration pneumonia.

  • Computed Tomography (CT): Highly recommended for detailed evaluation of nasal cavity, sinuses, and cribriform plate; superior for defining extent of lesions and surgical planning.

  • MRI (Magnetic Resonance Imaging): Excellent for soft tissue detail, especially for neural involvement or extent of tumors.

• Rhinoscopy: Using rigid and flexible rhinoscopes for direct visualization of the nasal passages and nasopharynx.- Timing: Ideally performed after imaging to understand the anatomy and extent of disease.

• Cytology: Microscopic examination of cells from discharge or biopsy for preliminary diagnosis.

• Biopsy: Histopathological examination of tissue samples for definitive diagnosis, especially for neoplasia.

• Culture: Fungal/Bacterial cultures of discharge or tissue to identify specific pathogens and guide antimicrobial/antifungal therapy.

Nasal Surgery

• Nasal Planum Resection:- Indication: Neoplasia (SCC, lymphoma, malignant histiocytosis, malignant melanoma, basal cell carcinoma, mast cell tumor) is the most common reason. Can also be used for reconstruction after trauma.

  • Maxillectomy: May be necessary in advanced cases involving surrounding bone.

  • Mucosal apposition: Mucosa is sutured to skin to prevent postoperative occlusion (stenosis).

• Rhinotomy: Surgical incision into the nasal cavity, used for curative or palliative purposes.- Dorsal Rhinotomy: Provides access to the nasal cavity and sinuses, commonly used for neoplasia or extensive disease.

  • Ventral Rhinotomy: Provides access to the ventral nasal cavity and choanae.

• Sinusotomy: Surgical incision into a sinus, often followed by placement of postoperative drains to prevent subcutaneous emphysema.

• Nasal Turbinectomy: Excision of nasal turbinates, often performed via dorsal rhinotomy for neoplasia or chronic rhinitis/sinusitis.

Nasal Surgery Risks and Complications

• Hemorrhage: Can be significant due to rich blood supply (dorsal, lateral, and major palatine arteries).

• Flap Necrosis: Death of tissue flap if blood supply is compromised.

• Oronasal Fistula: Abnormal connection between the oral and nasal cavities.

• Dehiscence: Surgical site opening.

• Stenosis of Airways: Narrowing of nasal passages.

• Inability to close mouth/breathe: Improper mucous to skin apposition can lead to difficulty breathing or inability to close the mouth effectively.

• Incomplete Resection/Local Recurrence (for neoplasia): High risk if tumor margins are not clear.

Brachycephalic Obstructive Airway Syndrome (BOAS)

• Definition: A congenital and progressive disorder affecting breeds with shortened and broadened skulls, leading to significant upper airway obstruction.

• Commonly Recognized Breeds: English Bulldog, French Bulldog, Pug, Shih Tzu, Pekingese, Boston Terrier, Boxer.

• Less Commonly Recognized Breeds: Chihuahua, Cavalier King Charles Spaniel, Maltese, Chow Chow, Yorkshire Terrier, Miniature Pinscher, Shar Pei.

• Cats: Persian, Himalayan.

Brachycephalic Anatomy

• Local Chondrodysplasia: A developmental abnormality of cartilage, which in brachycephalic breeds, affects skull development.

• Skull Development: Results in early ankylosis (fusion) of the basioccipital and basisphenoid bones, leading to a shortened and broadened skull.

• Soft Tissue Disproportion: The skull is shortened without a proportional decrease in the soft tissues of the head, causing crowding and obstruction of the airway.

• Inherited Components: Stenotic nares, hypoplastic trachea, elongated soft palate, and soft palate/epiglottis overlap are inherited anatomical components contributing to BOAS.

Four Components of BOAS

Primary/Early Disease Components (Surgical Correction Aims to Alleviate):

1. Stenotic Nares:- Impact: Air passage through nasal cavities accounts for 76.5% of airway resistance.

   • Mechanism: Abnormal anatomy causes external and internal resistance due to inability to dilate nostrils; can involve static and dynamic abnormalities.

   • Consequence: Greatly increased effort to inhale.

2. Elongated Soft Palate:- Significance: Most common and important component of BOAS.

   • Normal vs. Elongated: A normal soft palate should overlap the epiglottis by only 1-2 mm at the midline and extend to the mid-ventral 1/3 of the tonsillar crypt laterally.

   • Elongated Palate: Extends past the top of the epiglottis or the mid to lower part of the tonsillar crypt.

   • Clinical Sign: Leads to severe inspiratory dyspnea, characterized by stertor (snoring or gasping sound).

   • Grades: Can be classified as Normal, Mild, Moderate, or Severe.

• Primary Component (If Present):

1. Hypoplastic Trachea:- Description: Narrower than normal tracheal lumen.

   • Prevalence: Commonly seen in English Bulldogs.

   • Characteristics: Irregular, thick, firm cartilage rings with potential overlap of rings.

   • Consequence: Significantly increased airflow resistance.

   • Treatment: No direct surgical treatment for hypoplastic trachea itself.

   • Diagnosis: Tracheal diameter to thoracic inlet ratio (TD/TI) on thoracic radiographs. A smaller ratio indicates hypoplasia.

• Secondary/Progressive Component:

1. Laryngeal Collapse: Due to chronic negative pressure on laryngeal cartilages.- Stage I: Everted laryngeal saccules (edematous mucosa). Often seen early due to secondary changes from chronic inflammation.

   • Stage II: Collapse of the cuneiform cartilage. This indicates loss of cartilage rigidity (chondromalacia).

   • Stage III: Collapse of both the cuneiform and corniculate cartilage, leading to severe airway obstruction.

   • Prevalence: Reported in 8-50% of dogs evaluated for BOAS.

   • Clinical Sign: May cause stridor (high-pitched inspiratory sound), typically only in end stages.

Clinical Presentation of BOAS

• Age: Clinical signs often manifest around 2-3 years; English Bulldogs may present younger.

• Sex: Males (M) are often more affected than females (F).

• Clinical Signs: Often considered