Larynx, pharynx, trachea

Question 1

Anatomy: pharynx

Answer 1

• Boundaries:
  
  • Base of tongue
  • Retropharyngeal wall
  • Caudal extent of hard palate and the epiglottis
• Divided into oropharynx and nasopharynx and separated by soft palate
• A region; bounded by discrete structures
• Function–compresses bolus and with the tongue forces the bolus into the esophagus

Question 2

Anatomy: larynx

Answer 2

• Cartilages:
  
  • Esophagus
  • Thyroid
  • Cricoid
  • Arytenoid
• Hyoid apparatus

Question 3

Radiographic anatomy: pharynx/larynx views

Answer 3

• Many structures involving the larynx and pharynx can be identified on well-positioned and properly exposed radiographs
• Lateral view is most helpful
• In the VD view most structures are superimposed on the cervical spine (not helpful)

Question 4

Pharynx/larynx: Mineralization

Answer 4

• Difficult to discern laryngeal structures in animals 2-3 months old due to lack of mineralization
• Mineralization of all laryngeal structures is a normal aging change–seen as early as 1-3 years, occurs even earlier in large breeds
• Cricoid cartilage is 1st to become mineralized

Question 5

Pharynx/larynx: positioning and patient characteristics

Answer 5

• Obesity reduces air in the region–less contrast and increased difficulty interpreting lesions
• In neutral position in a lateral radiograph, the larynx is ventral to and ends at the level of C1 and C2
• Head position can greatly influence laryngeal position

Question 6

Pharynx/larynx: Incidental findings

Answer 6

• The depth and phase of respiration will also effect position of laryngeal structures
• Basihyoid bone and other hyoid bones (due to rad. positioning) are often mistaken for a foreign body

Question 7

Clinical manifestations of pharyngeal and laryngeal lesions

Answer 7

• Dysphagia
• Inspiratory dyspnea
• Stridor
• Change in the voice

Question 8

Tracheal anatomy

Answer 8

• Tubular semi-rigid midline structure
• Attached at larynx and carina
• Held in position by mediastinum and neck muscles
• Slightly more moveable in the cranial mediastinum

Question 9

Radiographic anatomy: trachea

Answer 9

• Easiest to evaluate on lateral view
• Use VD to assess displacement
• Thoracic trachea found on the right of the mediastinum
• Deviation to right is exaggerated in obese and brachycephalic breeds–do not mistake this for a mediastinal mass
• Slight divergence of the trachea from the spine in the normal dog
• Trachea may angle slightly ventrally at the caudal extent and into the carina
• In normal animals the trachea diameter does not vary significantly during respiration

Question 10

Trachea: mineralization

Answer 10

• Mineralization of the tracheal rings is a normal, degenerative or aging process
• Seen in large breeds, chondrodystrophic breeds, and in young dogs with no clinical sig.
• May increase with metastatic mineralization

Question 11

Trachea: radiographic positioning

Answer 11

• In a lateral view, the neck must remain in a neutral position
• Extension results in compression and narrowing of trachea at the thoracic inlet
• Flexion results in a bend in the cranial mediastinum–may result in a false diagnosis of a cranial mediastinal mass

Question 12

Clinical manifestations and lesions of the trachea

Answer 12

• Cough–“honking”
• Dyspnea
• Common lesions
  
  • Tracheal displacement
  • Neoplasia
  • Hypoplasia (congenital in English bulldog)
  • Tracheitis–no rad signs
  • Tracheal collapse

Question 13

Tracheal displacement

Answer 13

• Reliable sign of a mass lesion
• In the cervical regions the masses have to be large to result in displacement
• Larger lesions will result in compression of the trachea
  
  • Heart enlargement
  • Cranial mediastinal and tracheobronchial lymph nodes
  • May originate within the trachea

Question 14

Tracheal neoplasia

Answer 14

• Uncommon
• Osteochondromas and carcinomas are most frequent in the dog and cat
• Produce clinical signs of airway obstruction
• Appear as masses within the lumen
• Other differential diagnoses include polyp and abscessation

Question 15

Tracheal collapse

Answer 15

• Dynamic in nature
• Diameter varies with resp. cycle
• Toy breeds predisposed; weakening in tracheal rings
• Dynamic narrowing occurs in cervical trachea (thoracic inlet) during inspiration
• Dynamic narrowing occurs in thoracic trachea (carina) during expiration
• To evaluate trachea, films must be taken at inspiration and expiration
• Often coughing exaggerates the lesion
• Inducing a cough while performing flouroscopy may be required to demonstrate the lesion

Question 16

Pitfalls (trachea)

Answer 16

• Redundant trachealis dorsalis membrane
• Draping esophagus