Differential Diagnosis for Diploic Space Mass in an Infant
The most common diploic space lesions in infants are epidermoid/dermoid cysts and Langerhans cell histiocytosis, followed by vascular lesions and fibrous dysplasia. 1
Primary Differential Diagnoses
Most Common Entities
- Epidermoid/Dermoid Cysts: The most frequently encountered skull lesion in the pediatric population, typically presenting as a painless mass, most commonly in the occipital or frontal bones 1
- Langerhans Cell Histiocytosis (Eosinophilic Granuloma): Second most common, appearing as lytic lesions that can be locally aggressive and mimic malignancy on imaging 1, 2
Vascular Lesions
- Intraosseous Hemangioma: Benign vascular lesion within the diploic space that may require preoperative embolization if excision is planned 1, 3
- Sinus Pericranii: Rare congenital vascular malformation connecting intracranial and extracranial venous systems, typically seen at earlier ages 2
Developmental/Congenital Lesions
- Fibrous Dysplasia: Can present as early as 4 months of age with expansile lesions and dense calcification in the diploic space, appearing as painless progressively expanding bone swellings 4
- Aplasia Cutis Congenita: Rare congenital malformation affecting the skull, usually benign 2
Traumatic Sequelae
- Cephalohematoma: Post-traumatic collection that can calcify and mimic a mass 2
- Growing Skull Fracture: Post-traumatic lytic lesion that expands over time 2
Neoplastic Lesions (Less Common in Infants)
- Infantile Myofibroma: Rare benign fibrous lesion that can involve the skull 1
- Aneurysmal Bone Cyst: Expansile lytic lesion with fluid-fluid levels on MRI 2
Critical Diagnostic Approach
Imaging Strategy
- MRI with gadolinium contrast is the initial imaging modality of choice to characterize soft tissue components, intracranial extension, and relationship to adjacent structures 5, 6
- CT with contrast provides complementary information about bone involvement, cortical erosion, and calcification patterns 5, 2
- Look specifically for: cortical bone erosion, soft tissue components, intracranial extension, and multiplicity of lesions 3, 5
Age-Specific Considerations
- Patient age is the single most important demographic factor influencing the differential diagnosis of skull masses 3
- In infants specifically, congenital lesions (dermoid/epidermoid cysts, vascular malformations) and developmental disorders (fibrous dysplasia) are more likely than neoplastic processes 2, 4
Key Distinguishing Features
- Assess depth of involvement: Determine if the mass is superficial (scalp) versus deep (involving skull/diploic space), as deep masses require neurosurgical evaluation 3
- Evaluate for multiplicity: Multiple lesions suggest systemic conditions like Langerhans cell histiocytosis or metastatic disease 3, 5
- Clinical presentation matters: Most benign skull lesions present as painless masses, while infectious processes (osteomyelitis) tend to be locally aggressive with systemic symptoms 1, 2
Critical Pitfalls to Avoid
- Never perform biopsy or surgical intervention without adequate imaging (both MRI and CT) to characterize the lesion and exclude intracranial extension 5, 1
- Do not rely on conventional X-rays alone, as lytic lesions only become visible after more than 50% of trabecular bone loss 5
- Always assess for intracranial extension, which occurs rarely but changes surgical planning dramatically and was identified in only 1 of 19 cases in one pediatric series 1
- Consider infectious etiologies (osteomyelitis) in the appropriate clinical context, as these can mimic malignancy and require different management 2