What is the appropriate workup for a 3-year-old with a left neck submandibular mass that has doubled in size over 4 days, despite being on cephalexin (cephalexin), following a fever?

Workup for Rapidly Enlarging Submandibular Mass in a 3-Year-Old with Treatment Failure

This child requires immediate ultrasound of the neck as the initial imaging study, followed by urgent clinical reassessment for possible antibiotic change or surgical intervention, as the rapid doubling of mass size despite cephalexin therapy over 4 days indicates either antibiotic-resistant bacterial infection, abscess formation, or an alternative diagnosis requiring different management. 1

Immediate Clinical Assessment

The rapid progression (doubling in 4 days) with fever despite antibiotic therapy is a red flag that demands urgent evaluation. Key clinical features to assess immediately include:

• Overlying skin changes: erythema, warmth, fluctuance, or purple discoloration suggesting abscess or vascular lesion 2
• Systemic toxicity: high fever (>38.5°C), irritability, poor feeding, or lethargy 1
• Airway compromise: any stridor, drooling, or respiratory distress requiring immediate intervention 1
• Facial nerve function: weakness suggesting deep space infection or parotid involvement 2

Initial Imaging: Ultrasound First

Ultrasound of the neck is the most appropriate initial imaging study for a child with a neck mass. 1 This modality:

• Differentiates solid from cystic lesions and identifies abscesses requiring drainage 1
• Distinguishes lymphadenitis from congenital abnormalities, vascular malformations, or salivary pathology 1
• Provides color-flow Doppler assessment to characterize vascular flow in solid lesions 1
• Avoids radiation exposure and typically requires no sedation 1

If ultrasound findings are concerning for deep neck infection, complicated abscess, or malignancy, CT neck with IV contrast or MRI neck without and with IV contrast should be obtained for surgical planning. 1

Antibiotic Failure Analysis

Cephalexin is explicitly not recommended for respiratory tract infections or deep neck infections in children because first-generation cephalosporins have inadequate activity against S. pneumoniae with decreased penicillin susceptibility and lack coverage for common respiratory pathogens. 3, 4

The failure to respond after 4 days on cephalexin suggests:

• Resistant bacterial infection: likely S. aureus (including MRSA), Group A Streptococcus, or anaerobes requiring broader coverage 1
• Abscess formation: requiring surgical drainage in addition to antibiotics 1
• Alternative diagnosis: atypical mycobacterial infection, cat-scratch disease, or non-infectious etiology 2

Immediate Antibiotic Change

Switch immediately to amoxicillin-clavulanate 80 mg/kg/day divided three times daily as first-line therapy for presumed bacterial cervical lymphadenitis with treatment failure. 1, 4 This provides:

• Coverage for S. pneumoniae, including penicillin-resistant strains 1
• Activity against H. influenzae and Moraxella catarrhalis 1
• Anaerobic coverage for potential abscess 1

Alternative options if amoxicillin-clavulanate is contraindicated:

• Second-generation cephalosporin (cefuroxime-axetil) or third-generation cephalosporin (cefpodoxime-proxetil) 1, 3
• Note: Cefixime is explicitly NOT recommended 1

Consideration for Hospitalization and IV Antibiotics

Hospitalization with IV antibiotics should be strongly considered given:

• Rapid progression despite oral antibiotics 1
• Age <5 years with severe or complicated infection 1
• Potential need for surgical drainage if abscess is identified 1

Appropriate IV antibiotics include:

• Ampicillin-sulbactam or amoxicillin-clavulanate IV 1
• Cefuroxime or cefotaxime 1
• Add clindamycin or vancomycin if MRSA or severe infection suspected 1

Reassessment Timeline

Clinical improvement should be evident within 48-72 hours of appropriate antibiotic therapy. 1, 4 Assessment criteria include:

• Fever resolution (typically within 24-48 hours for bacterial infections) 1, 4
• Reduction in mass size and tenderness 1
• Improved oral intake and activity level 1

If no improvement occurs within 48-72 hours despite appropriate antibiotics, further investigation is mandatory, including consideration of:

• Surgical consultation for incision and drainage 1
• Aspiration or biopsy for culture and pathology 1
• Expanded imaging (CT or MRI) if not already obtained 1
• Alternative diagnoses including atypical infections, malignancy, or autoimmune conditions 1, 2

Critical Pitfalls to Avoid

• Do not continue cephalexin: First-generation cephalosporins are inadequate for this clinical scenario 3, 4
• Do not delay imaging: Ultrasound should be obtained urgently to guide management 1
• Do not assume all cephalosporins are equivalent: Second and third-generation agents have significantly better activity than cephalexin 3
• Do not wait beyond 48-72 hours without reassessment: Deterioration or lack of improvement mandates surgical evaluation 1, 4