Obstructive Sleep Apnea

Lane F. Donnelly, MD

DIFFERENTIAL DIAGNOSIS

Common

Enlarged Palatine Tonsils
Enlarged Adenoid Tonsils
Recurrent and Enlarged Adenoid Tonsils
Enlarged Lingual Tonsils
Glossoptosis
Hypopharyngeal Collapse

Less Common

Enlarged Soft Palate
Macroglossia

Rare but Important

Tongue-based Masses
Thyroglossal Duct Cyst
Artificial Airway (Mimic)

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

MR sleep studies: Combination of T1WI (static) and T2WI (static and dynamic cine)
- Depict both anatomic and dynamic motion abnormalities in children with obstructive sleep apnea (OSA)
- Most often performed in children who have persistent OSA despite previous surgery
  - e.g., previous palatine tonsillectomy and adenoidectomy
- When interpreting, it is important to identify both anatomic causes (enlarged tonsils) &/or collapse patterns (glossoptosis or hypopharyngeal collapse)
2 key anatomic areas for most causes of OSA
- Posterior nasopharynx
  - Airway bordered by soft palate anteriorly, nasal turbinates anteriorly and superiorly, adenoids posteriorly
  - Inferior border defined by inferior tip of uvula
- Retroglossal airway
  - a.k.a. hypopharynx
  - Aerated space bordered by posterior aspect of tongue anteriorly, posterior pharyngeal wall posteriorly, and inferior aspect of soft palate anteriorly
  - Inferior border is inferior extent (or base) of tongue

Helpful Clues for Common Diagnoses

Enlarged Palatine Tonsils
- Diagnosis made on physical inspection, not usually imaging diagnosis
  - Most patients referred for MR sleep studies already have had palatine tonsils removed
  - No published data on upper limits of normal measurement at imaging
- Round, well-defined, high T2 signal masses within palatine tonsillar fossa
  - If appear prominent and “bob” centrally with respiration and obstruct airway → enlarged
- Unlike adenoid tonsils, palatine tonsils do not recur after palatine tonsillectomy
Enlarged Adenoid Tonsils
- Natural history
  - Adenoid tonsils are absent at birth
  - Reach maximum size by 2-10 years
  - Shrink during 2nd decade of life
- Upper limit of normal size is 12 mm
Recurrent and Enlarged Adenoid Tonsils
- Adenoids not encapsulated tonsil, so small amounts of lateral tonsillar tissue always left after surgery
  - Recurrence of adenoid 1 of more common causes of recurrent OSA
  - Postoperative appearance: Central wedge triangular defect in central portion of tonsil
- > 12 mm in size and associated with intermittent collapse of posterior nasopharynx on cine images
  - Can be associated with secondary hypopharyngeal collapse secondary to negative pressure generated at obstruction of posterior nasopharynx
Enlarged Lingual Tonsils
- Previously thought to be rare cause of OSA, increasingly recognized as more common
- Surgically treatable; important to identify
- Not always easily appreciated on physical examination
- In most normal children, lingual tonsils range from nonperceptible to several mm
- In patients with previous palatine tonsillectomy and adenoidectomy, lingual tonsils can grow large
  - High propensity in patients with Down syndrome, obesity
- Appear as large, bilateral, high T2 signal masses at base of tongue
  - Can grow into 1 large dumbbell-shaped mass
  - Can grow superiorly into palatine fossa
  - Potentially confused with palatine tonsils if history of palatine tonsillectomy not known
Glossoptosis
- Defined as posterior motion of tongue during sleep
- Tongue is posteriorly positioned, and posterior wall of tongue abuts posterior pharyngeal wall, obstructing retroglossal airway
  - Tongue may also displace soft palate posteriorly and obstruct nasopharynx
- Occurs in children with macroglossia (large tongue), micrognathia (small mandible), or decreased muscular tone
  - e.g., Down syndrome, Pierre-Robin sequence, cerebral palsy
- Axial cine images show posterior motion of tongue but no change in left-to-right transverse diameter of retroglossal airway
- Important to differentiate glossoptosis from hypopharyngeal collapse as there are more and better surgical options for glossoptosis
Hypopharyngeal Collapse
- Primarily related to decreased muscular tone
- Secondary to negative pressure, secondary to more superior obstruction (e.g., enlarged adenoids)
- Axial cine images show dynamic and cylindrical narrowing of hypopharynx
  - All walls (left, right, anterior, posterior) collapse to center of retroglossal airway

Helpful Clues for Less Common Diagnoses

Enlarged Soft Palate
- Thickened and long soft palate possible cause of OSA
- No established quantitative imaging criteria for when soft palate too long or thick
- If soft palate draped over tongue and associated with collapse of airway on cine images → enlarged
- Edema from snoring can occur
  - Appears as increased T2 signal in soft palate centrally
  - Soft palate normally same signal intensity of tongue musculature, dark on T2

Helpful Clues for Rare Diagnoses

Artificial Airway (Mimic)
- Obscures and distorts anatomic structures being evaluated
  - May simulate pathology
- Try to avoid artificial airway when acquiring MR sleep studies