What are the potential etiologies and management options for a nodular lesion with a necrotic cap on the forehead in an adult patient with no significant past medical history, following a biopsy?

Nodular Lesion on Forehead with Necrotic Cap: Differential Diagnosis and Management

Primary Differential Diagnosis

The most critical priority is to exclude malignancy, particularly squamous cell carcinoma, basal cell carcinoma with necrosis, Merkel cell carcinoma, or metastatic disease, as these require urgent definitive treatment to prevent morbidity and mortality. 1

High-Priority Malignant Etiologies

• Squamous cell carcinoma with central necrosis - The forehead is a common site for cutaneous malignancies, and necrosis suggests aggressive behavior or larger tumor burden 1
• Merkel cell carcinoma - Presents as rapidly growing nodules on sun-exposed areas (head/neck in 50% of cases), often with overlying skin changes or ulceration; highly aggressive with significant mortality risk 1
• Basal cell carcinoma (nodular-ulcerative type) - Can present with central necrosis or ulceration, though typically slower growing 1
• Metastatic disease to skin - The scalp and forehead are vascular areas prone to metastatic deposits from internal malignancies; necrosis is common in metastatic lesions 2
• Cutaneous lymphoma (NK/T-cell type) - Extranodal NK/T-cell lymphomas commonly involve the head and neck with necrotic features; associated with tissue destruction 1

Benign/Reactive Etiologies

• Nodular fasciitis - Benign reactive proliferation that can occur in the head/neck region, more common in children/adolescents but can occur in adults; typically rapidly growing over weeks 3
• Keratoacanthoma - Rapidly growing nodule with central keratin-filled crater that can mimic squamous cell carcinoma; typically reaches maximum size within 6-8 weeks 4
• Infected epidermoid/pilar cyst - Can present with overlying necrotic changes when ruptured or infected 1

Immediate Diagnostic Workup

Clinical Assessment Priorities

• Document growth rate - Rapid growth over days to weeks suggests malignancy (Merkel cell, aggressive SCC) or reactive process (nodular fasciitis, keratoacanthoma) 1, 3
• Assess for pain, tenderness, or dysesthesia - Pain or regional dysesthesia may indicate perineural invasion, particularly concerning for aggressive malignancies 5
• Examine for facial nerve function - Any facial weakness suggests deep invasion or perineural spread of malignancy 5
• Palpate regional lymph nodes - Preauricular, parotid, and cervical lymphadenopathy suggests metastatic spread 1
• Complete skin examination - Look for additional suspicious lesions or primary cutaneous malignancy that could metastasize to this site 6

Biopsy Strategy

Proceed immediately with excisional biopsy or deep punch biopsy (not shave biopsy) to obtain full-thickness tissue including the necrotic cap and viable tumor margins for accurate diagnosis and staging. 1, 7

• Excisional biopsy is preferred for lesions <2 cm where complete removal with narrow margins is feasible, providing both diagnosis and potential treatment 1
• Incisional/punch biopsy (4-6mm minimum) should include the edge of the lesion to capture viable tissue, as necrotic centers often delay diagnosis; avoid sampling only necrotic material 1, 7
• Core needle biopsy is NOT recommended for initial diagnosis of suspected primary cutaneous malignancy on the forehead, as it provides insufficient tissue architecture 1, 7
• FNA alone is insufficient for initial diagnosis of solid cutaneous lesions and should not be used 1, 8

Pathology Requirements

• Request comprehensive immunohistochemistry panel including: cytokeratin 20 (CK20) for Merkel cell carcinoma, TTF-1 to exclude metastatic lung cancer, CD56 and synaptophysin for neuroendocrine tumors, and lymphoid markers (CD2, CD3, CD20, CD56) if lymphoma suspected 1
• Ensure adequate tissue for ancillary studies - Submit fresh tissue in appropriate media if lymphoma is in the differential (RPMI medium for flow cytometry) 1
• Request assessment of depth of invasion, ulceration, mitotic rate, and lymphovascular invasion - Critical for staging cutaneous malignancies 1, 4

Imaging Considerations

• Imaging is NOT required before biopsy for a superficial forehead nodule without clinical evidence of deep invasion or lymphadenopathy 1, 5
• Order MRI with and without contrast if there is clinical suspicion of deep tissue invasion, bone involvement, or perineural spread (pain, dysesthesia, facial nerve dysfunction) 5
• Obtain chest CT if Merkel cell carcinoma or high-grade malignancy is confirmed on biopsy, as part of staging workup 1, 5

Critical Management Pitfalls to Avoid

• Do not perform shave biopsy - This technique is inadequate for lesions with necrosis and may prevent accurate depth assessment and staging, potentially compromising definitive treatment 7, 4
• Do not delay biopsy for imaging - Tissue diagnosis is the priority; imaging without histologic confirmation wastes time and resources 1, 5
• Do not assume benign diagnosis based on clinical appearance alone - Necrosis in a nodular lesion is concerning for malignancy until proven otherwise 1, 2
• Do not sample only the necrotic center - Biopsy must include the viable edge of the lesion to avoid non-diagnostic results 1, 7
• Do not use FNA as the initial diagnostic modality for solid cutaneous lesions - It has limited accuracy and provides insufficient tissue architecture 1, 8

Post-Biopsy Management Algorithm

If Malignancy Confirmed

• Merkel cell carcinoma: Wide local excision with 1-2 cm margins, sentinel lymph node biopsy, and adjuvant radiation therapy for tumors ≥2 cm; refer to multidisciplinary oncology team urgently 1
• Squamous cell carcinoma: Wide excision with margin assessment, consider Mohs surgery for high-risk features (>2 cm, poorly differentiated, perineural invasion); evaluate for nodal disease 1
• Metastatic disease: Staging workup to identify primary source; systemic therapy typically required 2
• Cutaneous lymphoma: Staging workup, referral to hematology-oncology; may require systemic chemotherapy and radiation 1

If Benign Diagnosis

• Nodular fasciitis: Simple excision is curative; no additional treatment needed 3
• Keratoacanthoma: Complete excision with margin assessment to exclude well-differentiated SCC 4
• Infected cyst: Complete excision after inflammation resolves 1