What could be causing the persistent mild swelling above the surgical scar on the right cheek 18 days after excision of a right‑sided facial squamous‑cell carcinoma despite a 13‑day course of flucloxacillin 500 mg four times daily?

Persistent Swelling After Facial Squamous Cell Carcinoma Excision

The persistent mild swelling 18 days post-excision most likely represents normal postoperative edema, but you must rule out residual/recurrent tumor, surgical site infection (despite antibiotic treatment), hematoma/seroma formation, or a pathergy-like reaction with eruptive squamous cell carcinoma.

Most Critical Differential: Residual or Recurrent Disease

• Incomplete excision of facial SCC occurs in 6-8% of cases, with head and neck locations being the highest risk site for positive margins 1, 2
• The cheek is a particularly high-risk location, with incomplete excision rates significantly elevated in facial locations including cheeks, ears, temples, and nose 2
• Facial SCCs require histologically confirmed negative margins of at least 4-6 mm for high-risk tumors, and inadequate margins are strongly associated with local recurrence 3
• If margins were not confirmed histologically as negative, residual tumor must be considered as the cause of persistent swelling 3

Rare but Critical: Eruptive Post-Operative SCC (Pathergy-Like Reaction)

• Eruptive SCCs can develop within healing surgical sites as early as 6 weeks post-excision, presenting as rapidly growing keratotic nodules even when original margins were histologically clear 4
• This pathergy-like reaction represents a rare but significant postoperative complication where new SCCs develop acutely in wound margins 4
• At 18 days post-op, this is on the early end but within the timeframe for this phenomenon 4

Infection Considerations

• While flucloxacillin was given for 13 days, persistent swelling after appropriate antibiotic therapy suggests either inadequate source control, resistant organism, or non-infectious etiology 5
• True bacterial infection would typically show progressive erythema, warmth, purulent drainage, or systemic signs—not isolated mild swelling 5
• If infection is suspected, consider imaging (ultrasound or MRI) to evaluate for abscess or fluid collection requiring drainage 3

Immediate Diagnostic Approach

Perform the following evaluation now:

• Biopsy any clinically suspicious area of the wound or swelling immediately to rule out residual/recurrent SCC before proceeding with any further management 6
• Examine the original pathology report to confirm margin status—if margins were positive or close (<4 mm), residual tumor is highly likely 3
• Obtain ultrasound of the area to differentiate solid tissue (tumor) from fluid collection (seroma/hematoma/abscess) 3, 5
• Palpate regional lymph nodes (preauricular, submandibular, cervical) for metastatic disease, as facial SCCs have significant lymphatic spread potential 3

Management Algorithm Based on Findings

If biopsy shows residual/recurrent SCC:

• Re-excision with wider margins (minimum 6 mm for facial high-risk SCC) with intraoperative margin assessment 3
• Consider Mohs micrographic surgery for facial location to maximize tissue preservation while ensuring complete excision 3
• Do not perform complex reconstruction until negative margins are confirmed 6

If imaging shows fluid collection:

• Ultrasound-guided aspiration for diagnosis and potential therapeutic drainage 5
• Send aspirate for culture if infection is suspected, though routine culture is not indicated for simple seromas 5

If evaluation is negative for tumor and infection:

• Normal postoperative edema can persist for weeks, particularly in facial surgery 6
• Continue observation with close follow-up every 2-4 weeks 3
• Any change in character (firmness, nodularity, rapid growth) mandates immediate re-biopsy 4

Critical Pitfalls to Avoid

• Never assume persistent swelling is benign edema without histologic confirmation that original margins were adequate 3, 1
• Do not perform complex flap reconstruction or skin grafting until you have definitively ruled out residual tumor 6
• Facial SCC locations have the highest incomplete excision rates—always verify margin status 1, 2
• Be aware that well-differentiated SCCs can recur locally even with apparently adequate initial treatment 7, 8
• Document a specific follow-up plan with clear criteria for re-evaluation 5