Likely Diagnosis: Congenital Dermal Sinus Tract with Secondary Infection
This is most likely an infected congenital dermal sinus tract (DST) on the occipital scalp, and this child needs urgent neurosurgical evaluation and imaging to rule out intracranial extension before the infection spreads to the central nervous system.
Clinical Reasoning
The presentation is highly characteristic of a dermal sinus tract:
- Chronic draining lesion present since infancy (over 1 year duration)
- Occipital location (classic site for cranial DSTs)
- Expressible material progressing from white (keratin debris) to yellow (purulent, indicating infection)
- Regional lymphadenopathy (posterior cervical node responding to chronic infection)
Cranial DSTs are congenital malformations where a tract extends from the skin surface toward deeper structures, potentially reaching the skull base or even penetrating intracranially 1. Parieto-occipital DSTs frequently have intracranial extension through a midline occipital skull defect and can end in relation to the occipital lobes or posterior fossa 1.
Critical Danger: Intracranial Infection Risk
The progression from white to yellow discharge signals bacterial superinfection, which is the most dangerous complication of DSTs. These tracts serve as a direct portal for skin bacteria to cause meningitis, subdural empyema, or brain abscess 1, 2, 3. The swollen lymph node confirms active infection is present.
Common pitfall: Dismissing this as a simple scalp infection or cyst. Unlike superficial lesions, DSTs can communicate directly with the CNS, making seemingly minor infections potentially life-threatening 2, 3.
Immediate Diagnostic Workup Required
MRI with and without contrast is the primary imaging modality to:
CT scan provides complementary information:
Do NOT attempt incisional biopsy or aspiration - this frequently leads to persistent clinical disease, sinus tract formation, and chronic drainage 4. Fine needle aspiration for diagnosis is acceptable if needed, but incisional biopsy should be avoided.
Definitive Treatment
Complete surgical excision is the only curative treatment 4, 1, 3. The procedure must include:
- Excision of the entire tract from skin to its deepest extent
- Removal of any associated dermoid cyst
- Excision of the skull defect if present
- Careful inspection to ensure no intracranial communication remains
Systemic antibiotics are essential given the current infection:
- Start empiric broad-spectrum coverage (typically targeting Staphylococcus aureus and other skin flora)
- Adjust based on intraoperative cultures
- Continue for 2-4 weeks depending on extent of infection 3, 5
Differential Considerations (Less Likely)
While the presentation strongly suggests DST, other possibilities include:
- Pilonidal sinus of scalp (extremely rare, usually post-traumatic) 6
- Actinomycosis (chronic infection with sulfur granules, but typically in adults) 7
- Infected dermoid cyst without tract (less likely given chronic drainage pattern) 5
Urgency of Referral
This requires urgent (within 24-48 hours) neurosurgical consultation, not routine referral. The combination of chronic drainage, purulent discharge, and occipital location in an 18-month-old creates significant risk for CNS infection. Delaying diagnosis and treatment increases the risk of meningitis, brain abscess, or other intracranial complications that carry substantial morbidity and mortality 2, 3.
Do not wait for the infection to "improve" with antibiotics alone - the underlying structural abnormality requires surgical correction to prevent recurrent infections and potential catastrophic complications.