Management of Newborn Neck Mass Resolving Within One Week
A neck mass in a newborn that spontaneously resolves within one week is most consistent with sternomastoid tumor of infancy (fibromatosis colli) and requires only clinical observation without imaging or biopsy.
Most Likely Diagnosis
The clinical presentation strongly suggests sternomastoid tumor of infancy (SMTI), which is the most common cause of neck mass in the perinatal period 1. This benign condition typically:
- Presents between 1-4 weeks of age 1
- Resolves spontaneously with conservative management 1
- Is associated with birth trauma in the majority of cases 1, 2
- Represents benign fibroblastic proliferation within the sternocleidomastoid muscle 2
Recommended Management Approach
Initial Assessment (No Imaging Required)
For a neck mass that resolves within one week in a newborn, no diagnostic workup is necessary since the rapid resolution confirms the benign nature 1. However, if the mass were still present, you should assess for:
- Birth history: Difficult delivery, breech presentation, or forceps use strongly support SMTI 1, 2
- Location: Mass within the sternocleidomastoid muscle 1
- Associated findings: Torticollis or facial asymmetry may be present 1
- Age at presentation: Typically 1-6 weeks of age 1, 2
Conservative Management Protocol
When SMTI is suspected clinically (before spontaneous resolution):
- Massage and controlled stretching of the neck is the primary treatment 1
- No biopsy is needed when clinical assessment is consistent with SMTI 1
- Complete resolution of the mass, torticollis, and facial asymmetry occurs with conservative management 1
Alternative Diagnoses to Consider
While SMTI is most likely given the rapid resolution, other congenital neck masses in newborns include 3:
- Thyroglossal duct cysts (most common overall congenital neck mass in children) 3
- Branchial cleft anomalies 3
- Dermoid cysts 3
- Vascular lesions such as hemangiomas 3
However, these typically do not resolve spontaneously within one week, making them unlikely in this scenario.
When to Pursue Further Workup
Ultrasound is the preferred initial imaging modality for pediatric neck masses when workup is indicated 4. Indications for imaging would include:
- Mass persisting beyond 2-4 weeks without decrease in size 5
- Rapid enlargement or development of respiratory distress 6
- Hard, fixed, or supraclavicular location 5
- Size >2 cm 5
- Accompanying systemic symptoms 5
CT or MRI with contrast should be reserved for suspected malignancy or deep neck infection requiring surgical intervention 4.
Critical Pitfalls to Avoid
- Do not perform open biopsy without imaging and specialist evaluation, as this can worsen outcomes if malignancy is present 7
- Do not prescribe empiric antibiotics without clear signs of infection, as this delays diagnosis and provides false reassurance 7, 5, 8
- Do not assume all cystic masses are benign without definitive diagnosis, as up to 80% of cystic neck masses in adults >40 years are malignant (though this is rare in newborns) 7
Follow-Up Recommendations
Since the mass resolved within one week:
- No further follow-up is required for this specific episode 1
- Parents should be educated to monitor for recurrence 4
- If the mass recurs or a new mass develops, reassessment is warranted 4
The spontaneous resolution within one week provides strong reassurance that this was a benign, self-limited process consistent with SMTI rather than a concerning pathology requiring intervention 1.