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Retropharyngeal abscess

Retropharyngeal abscess is a potentially life-threatening deep neck space infection that predominantly affects children under 5 years old and results from drainage of infections from the nasopharynx, oropharynx, paranasal sinuses, or middle ear into the retropharyngeal space.

Key Images

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Look For First
  • Low attenuation symmetric fluid collection filling the retropharyngeal space side-to-side on CT (or high T2 signal centrally on MRI)
  • Thick enhancing rim peripherally on contrast-enhanced imaging
  • Widening and distension of the prevertebral soft tissue space
  • Diffusion restriction on DWI (increased b=1000 signal and low ADC values) on MRI
Key Image Findings
  • CT demonstrates symmetric low attenuation purulent fluid filling the retropharyngeal space; abscess may be eccentrically limited to one side due to midline raphe anatomy.
  • Thick peripheral enhancement on contrast CT differentiates true abscess from simple effusion or cellulitis.
  • Distension and widening of the retropharyngeal space with displacement of adjacent structures is a key finding.
  • MRI T1 shows central low to intermediate signal; T2 demonstrates central high signal with peripheral gadolinium enhancement on T1 C+.
  • DWI/ADC sequences show diffusion restriction (increased signal on b=1000 images and low ADC values) confirming presence of pus.
  • Plain radiographs show prevertebral soft tissue widening but cannot reliably distinguish abscess from effusion or cellulitis.
  • Ultrasound with high-resolution linear transducer in transverse orientation shows complex hypoechoic collection with poorly defined irregular periphery, loss of organized tissue echotexture, and expansion of prevertebral space.
  • CT has a not insignificant false negative rate (13%) and false positive rate (10%) for detecting pus, so clinical correlation is essential.
Differential Diagnosis
  • Retropharyngeal effusion: low attenuation fluid without peripheral enhancement; arises after infection elsewhere, radiation, or calcific tendinitis without requiring surgical drainage.
  • Suppurative retropharyngeal lymph node: rim-enhancing lateral retropharyngeal node with central hypoattenuating focus; often responds to antibiotics alone, particularly if the central focus is small.
  • Prevertebral abscess: usually secondary to discitis/osteomyelitis; careful evaluation of vertebral bodies and disc spaces on imaging is important.
  • Retropharyngeal hematoma: shows blood density/signal on CT/MRI; usually occurs in adults and associated with trauma or Capps triad.
  • Acute calcific prevertebral tendinitis: retropharyngeal effusion without marginal enhancement; calcification may be visible in longus capitis and colli muscles.
  • Mass involving retropharyngeal space (hemangioma, tumor) or retropharyngeal pseudothickening and angioedema: require clinical and imaging correlation to differentiate from infection.
Discussion

Retropharyngeal abscesses most commonly affect children under 5 years due to prominent retropharyngeal lymphoid tissue and frequent middle ear/nasopharyngeal infections.

Infection pathophysiology proceeds from lymph node enlargement (reactive lymphadenopathy) to edema (presuppurative phase) to liquefactive necrosis and pus formation (suppurative phase).

The lateral retropharyngeal lymph node group is most commonly affected and may rupture into the retropharyngeal space to form an abscess.

Clinical presentation varies from nonspecific symptoms (fever, irritability, poor feeding) to dramatic features (drooling, stridor, neck swelling) that may mimic epiglottitis.

Serious complications include posterior extension to prevertebral space/discitis/osteomyelitis, lateral extension with carotid artery involvement (hemorrhage, pseudoaneurysm, thrombosis), anterior airway compromise, and inferior extension to mediastinum.

MRI has superior contrast resolution and can assess diffusion restriction and vascular complications; CT is faster for airway assessment but has false negative (13%) and false positive (10%) rates for detecting pus.

Reporting Pearls

Describe the collection as symmetric low attenuation fluid with thick peripheral enhancement and prevertebral space distension on CT; emphasize the peripheral enhancement pattern to distinguish true abscess from nonenhancing effusion or cellulitis, and comment on carotid sheath relationship and absence of vascular complications when present.

Pitfalls
  • Confusing retropharyngeal abscess with retropharyngeal effusion: effusion lacks peripheral enhancement and does not require surgical drainage, whereas true abscess shows rim enhancement and typically requires drainage.
  • Misinterpreting suppurative retropharyngeal lymph node as diffuse abscess: lymph nodes are usually lateral and rim-enhancing and may respond to antibiotics alone without surgery.
  • Relying solely on imaging to diagnose abscess: CT has a 13% false negative rate for pus detection, so clinical presentation and possible surgical exploration may be necessary despite negative imaging.
  • Overlooking vascular complications: careful assessment of the carotid sheath relationship and evaluation for signs of thrombosis, pseudoaneurysm, or stenosis is essential as these can lead to life-threatening hemorrhage.
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