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Answer: D. Subperiosteal abscess

Diagnosis: Retroauricular subperiosteal abscess, as a complication of otitis media and coalescent mastoiditis.

Imaging Features Discussion:

• Look for asymmetry. Compare the normal left temporal bone with the grossly abnormal right.
  
• The axial T2 weighted image demonstrates increased signal consistent with edema and fluid in the mastoid air cells. There is extension of the abnormality through the lateral wall of the mastoid, with an adjacent subperiosteal fluid collection (deep to the auricle of the right ear).
• Axial T1 post contrast image shows enhancement in the mastoid air cells and adjacent subperiosteal space, consistent with inflammatory change and proteinaceous debris.
• Coronal T1 post contrast image demonstrates enhancement in the region of the middle ear, consistent with inflammation. Subperiosteal abscesses may arise as complications of otitis media.
• Additional coronal T1 post contrast image at a more posterior level demonstrates enhancement in the mastoid air cells and adjacent subperiosteum.

Discussion:

• Acute mastoiditis is a serious complication of acute otitis media in young children.
  • Incidence has decreased considerably since the introduction of antibiotics.
  • However, clinical awareness of the entity remains critical as there are a variety of highly morbid consequences that may occur.
  • The mastoid air cells are connected to the middle ear by the aditus and antrum. When this is obstructed by edema in the middle ear, mastoiditis occurs.
• Clinical features: Mastoiditis may be suspected when there is:
  • Persistend otorrhea beyond 3 weeks.
  • Persistent pain localized deep in or behind the ear.
  • Hearing loss
• Mastoiditis may progress in several ways if untreated.
  • Periostitis occurs when infection spreads to the adjacent periosteum.
  • Acute mastoiditis with osteitis (coalescent mastoditis) occurs when there is necrosis of bony septa and loss of air cell walls. The mastoid loses its aerated structure and becomes a pus filled cavity.
  • Use of broad spectrum antibiotics for otitis media may result in a "masked" mastoiditis that is smoldering in course and difficult to detect.
• Coalescent mastoiditis may spread in several directions.
  
  • Anterior spread through the aditus ad antrum may decompress pus into the middle ear, leading to spontaneous resolution.
  • Posterior spread to the occipital bone can lead to osteomyelitis of the calvarium (Citelli abscess).
  • Spread inferiorly and anteriomedially along the digastric and sternocleidomastoid muscles can lead to Bezold's abscesses, which are deep in the neck and difficult to palpate clinically.
  • Lateral spread, as seen in this case, can produce a subperiosteal abscess.
• Subperiosteal abscess
  • When coalescent mastoidis has occurred, the external mastoid cortex should be evaluated for evidence of osteolysis.
  • The abscess can extend toward the external auditory canal, spread along the zygomatic bone, or have a postauricular location.
• Further complications to be aware of:
  • Intracranial spread is particularly concerning-- meningitis; epidural, subdural, and intraparenchymal abscesses; vascular thrombosis may occur
  • Osteomyelitis
  • Deep neck abscesses (Bezold's abscesses, from spread through the inferior mastoid tip).
    • Bezold's abscess, with erosion of the inferior mastoid tip, and a large neck abscess resulting from inferior tracking along the sternocleidomastoid muscle (from AJR, Dec 1998)
      
    • 

Treatment:

• Acute mastoiditis with periostitis and coalescent mastoiditis are referred to as Acute Surgical Mastoiditis (ASM). Surgery is necessary.
• Mastoidectomy with insertion of a tympanostomy is performed to remove areas of coalescence in the temporal bone.
  
• Antibiotic coverage is also needed, typically with vancomycin and ceftriaxone initial therapy as drug resistance is common.
• Abscess drainage.

References

1. Vasquez et al, "Imaging of Complications of Acute Mastoiditis in Children" Radiographics 2003.

2. Parker, Jennifer, "Acute Mastoiditis" Otolarngology grand rounds, Feb 3, 1994

4. Devan, PP, "Middle Ear, Mastoiditis" Emedicine 2006.

3. Castillo et al, "Imaging of Bezold's Abscess" American Journal of Radiology, Dec 1998.

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