What is the likely diagnosis of a posterior neck subcutaneous mass located between the neck and shoulder in a patient immobilized in a cervical collar for two months after a C2 fracture?

Likely Diagnosis: Pressure-Related Soft Tissue Mass from Cervical Collar Immobilization

The most likely diagnosis is a benign soft tissue mass—either a lipoma, epidermoid cyst, or localized subcutaneous edema/fibrosis—caused by prolonged pressure and friction from the cervical collar worn for two months after the C2 fracture. However, given the location and duration, this mass must be evaluated using the high-risk neck mass protocol to exclude malignancy before assuming a benign etiology.

Why This Context Changes the Clinical Approach

• Prolonged cervical collar immobilization is a well-recognized cause of pressure-related skin and soft tissue complications, including pressure ulcers, localized edema, and reactive subcutaneous masses 1, 2.
• The posterior neck region between the neck and shoulder is a common site of collar-related pressure injury because the rigid collar edge creates focal mechanical stress 1.
• However, the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) guidelines mandate that any neck mass in an adult must be risk-stratified regardless of presumed etiology, because missing a malignancy has catastrophic consequences for morbidity and mortality 3, 4.

Immediate Risk Stratification Required

You must assess the following high-risk features to determine whether urgent imaging and specialist referral are needed 3, 4:

High-Risk Physical Examination Features

• Size > 1.5 cm in longest diameter 3, 4
• Firm or hard consistency (suggests malignancy rather than soft edema) 3, 4
• Fixation to adjacent tissues (indicates possible capsular invasion) 3, 4
• Ulceration of overlying skin (suggests capsular breach or cutaneous extension) 3, 4
• Duration ≥ 2 weeks without significant fluctuation 3, 4

High-Risk Patient Demographics

• Age > 40 years markedly increases the probability of head-and-neck squamous cell carcinoma 3, 4, 5
• Tobacco and alcohol use act synergistically to raise malignancy risk 3, 4

Associated Symptoms Suggesting Occult Primary Malignancy

• Throat pain, dysphagia, ipsilateral otalgia with normal ear exam, voice changes, unexplained weight loss, ipsilateral hearing loss, nasal obstruction, or epistaxis 3, 4

Management Algorithm

If ANY High-Risk Feature Is Present:

1. Order contrast-enhanced CT of the neck immediately (or MRI with contrast if CT is contraindicated) 3, 4, 5. This is a strong recommendation from AAO-HNS 3.

2. Refer urgently to otolaryngology concurrently with imaging—do not wait for imaging results before referral 4, 5.

3. Do NOT prescribe empiric antibiotics unless there are clear signs of bacterial infection (localized warmth, erythema, marked tenderness, fever > 101°F) 4, 5. Most adult neck masses are neoplastic, and unnecessary antibiotics delay cancer diagnosis, worsen outcomes, and promote antimicrobial resistance 4, 5.

4. Fine-needle aspiration (FNA) is the initial tissue diagnostic procedure if imaging does not provide a definitive diagnosis; FNA must be performed before any open biopsy 3, 4, 5.

5. Targeted endoscopic examination of the larynx, base of tongue, and pharyngeal mucosa should be performed by the otolaryngology specialist to search for an occult primary tumor 4, 5.

If NO High-Risk Features Are Present:

1. Document the exact size (in centimeters), consistency (soft vs. firm), mobility (mobile vs. fixed), presence or absence of tenderness, and overlying skin appearance 4.

2. Educate the patient on warning signs that would trigger immediate re-evaluation: enlargement of the mass, new dysphagia, voice change, ipsilateral ear pain, unexplained weight loss, or fever 4.

3. Arrange structured follow-up in 2–3 weeks to assess for resolution or progression 3, 4. If the mass persists unchanged, enlarges, or recurs, transition to the high-risk pathway with imaging and specialist referral 4.

4. Consider removing or adjusting the cervical collar if the fracture is stable and the immobilization period is complete, as this may allow a pressure-related mass to resolve 1, 2.

Critical Pitfalls to Avoid

• Do not assume the mass is benign simply because it appeared during collar use. Metastatic squamous cell carcinoma, lymphoma, and other malignancies can present as posterior neck masses and may coincidentally appear during collar immobilization 4, 6.

• Do not assume a cystic appearance on imaging or FNA excludes malignancy. Metastatic squamous cell carcinoma frequently presents as a cystic neck mass 3, 4, 5.

• Do not delay imaging or specialist referral by trialing antibiotics when infection is not clinically evident 4, 5.

• Do not perform an open biopsy before completing FNA, imaging, and endoscopic evaluation, as premature open biopsy can compromise oncologic management if the mass represents a metastatic node 3, 4, 5.

Differential Diagnosis in This Context

Most Likely Benign Etiologies (if low-risk features):

• Lipoma (most common benign soft tissue mass; soft, mobile, non-tender) 7
• Epidermoid cyst (firm, mobile, may have central punctum) 7
• Localized subcutaneous edema or fibrosis from chronic collar pressure 1, 2

Malignant Etiologies That Must Be Excluded (if high-risk features):

• Metastatic squamous cell carcinoma from head-and-neck primary sites (most common malignant cause in adults > 40 years) 3, 4, 5
• Lymphoma (requires core needle biopsy rather than FNA for diagnosis) 5
• Cutaneous malignancy (melanoma or squamous cell carcinoma) with nodal metastasis 3, 4

Rare Considerations:

• Unrecognized C1 lateral mass fracture can cause posterior neck pain and may be missed on plain radiographs, but typically does not present as a palpable mass 8
• Cervical chordoma (rare; presents with lytic-sclerotic bone destruction on CT and heterogeneous signal on MRI) 9

Summary of Evidence Quality

The AAO-HNS clinical practice guideline 3 is the highest-quality evidence for this scenario and provides a strong recommendation for contrast-enhanced imaging in high-risk neck masses. The ACR Appropriateness Criteria 7 support CT as the preferred modality for deep or complex soft tissue masses. The Praxis Medical Insights summaries 4, 5 synthesize these guidelines and emphasize antibiotic stewardship and the importance of not delaying cancer diagnosis.