What is the most appropriate next step in managing a 62-year-old man with a 1.8 cm subcutaneous circumscribed mass around the left sternocleidomastoid muscle (SCM) that is not mobile or tender?

Fine Needle Aspiration Biopsy is the Most Appropriate Next Step for a Neck Mass in the Sternocleidomastoid Muscle

Fine needle aspiration biopsy (FNAB) is the most appropriate next step in managing this 62-year-old man with a 1.8 cm subcutaneous mass in the left sternocleidomastoid muscle. 1

Rationale for FNAB

The approach to this patient's neck mass should follow a systematic diagnostic algorithm:

1. Patient Characteristics and Risk Factors:

   • 62-year-old male
   • Former smoker (quit >10 years ago)
   • No family history of malignancy or lymphoma
   • Mass present for at least 2 weeks

2. Physical Examination Findings:

   • 1.8 cm subcutaneous circumscribed mass
   • Located in mid-portion of left sternocleidomastoid muscle
   • Not mobile but not significantly fixed
   • Non-tender

3. Imaging Results:

   • CT scan confirms the mass but is not definitive for lymph node

Why FNAB is the Optimal Choice:

According to the UK guidelines for soft tissue masses, "the standard approach to establish a histopathological diagnosis of a suspicious soft tissue mass is by percutaneous core needle biopsy" 1. For a neck mass with these characteristics:

• FNAB provides tissue diagnosis with minimal invasiveness
• The procedure can be performed under ultrasound guidance for accuracy
• It allows for cytological evaluation to determine if the mass is benign or malignant
• It helps distinguish between lymph node, soft tissue tumor, or other pathologies

Alternative Approaches and Why They're Less Appropriate

1. Antibiotic and Reevaluation in Two Weeks:

   • Not appropriate as there are no signs of infection (no tenderness, no fever mentioned)
   • Delaying diagnosis for a mass in a 62-year-old with smoking history increases risk if malignant

2. Excisional Biopsy:

   • Too aggressive as an initial step
   • Guidelines state: "It would only be in exceptional circumstances that an incision biopsy would be necessary to gain adequate tissue for a pre-treatment diagnosis" 1
   • Should be reserved for cases where FNAB is non-diagnostic

3. Incisional Biopsy:

   • More invasive than necessary for initial diagnosis
   • Higher risk of complications
   • Guidelines recommend this only after discussion in a sarcoma specialist unit 1

Diagnostic Considerations

The differential diagnosis for this neck mass includes:

• Soft tissue sarcoma
• Metastatic carcinoma
• Lymphoma
• Benign soft tissue tumors (lipoma, angioleiomyoma)
• Ectopic tissue (thyroid, parathyroid, thymus)
• Inflammatory/infectious process

Several case reports document rare entities presenting as masses within the sternocleidomastoid muscle, including parathyroid adenoma 2, angioleiomyoma 3, lipoma 4, ectopic thymus 5, and nodular fasciitis 6.

Important Clinical Pearls

• Biopsy Planning: The biopsy should be planned so that the biopsy tract can be safely removed during definitive surgery if malignancy is found 1
• Multiple Cores: Multiple cores should be taken to maximize diagnostic yield 1
• Image Guidance: Ultrasound guidance improves accuracy and safety of the procedure
• Specialist Referral: Consider referral to a sarcoma center if there is high suspicion for soft tissue sarcoma

Next Steps After FNAB

Based on the FNAB results:

• If benign: Consider observation or complete excision depending on the specific diagnosis
• If malignant: Complete staging and referral to appropriate specialists (surgical oncology, radiation oncology, medical oncology)
• If non-diagnostic: Proceed to core needle biopsy or excisional biopsy

By starting with FNAB, you provide the most efficient pathway to diagnosis while minimizing patient risk and preserving options for definitive management.