Case of the Week: January 15-January 22, 2009

Infant with lump on head

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Case Details

What is the most likely diagnosis?

Study demonstrates a fluid filled cyst in the scalp resulting in erosion of the calvarial vault on the external surface. The erosion of the external surface of the bone indicates that the epicenter of the mass is in the scalp, not inside the calvarial vault. No extension into the calvarial vault is seen. There is no definite fat or calcium on MR or CT within the mass

Answer

Diagnosis: Dermoid Cyst

     Dermoids/Epidermoids are a result of congenital dermal or epidural rests or focal expansion of a dural sinus or can be acquired from implantation by prior puncture or surgery.

 Dermoids can contain sebum, blood, fat, bone or soft tissue.  Epidermoids can look very similar and are the two entities are grouped together. 

 Epidermoids do not contain the skin appendages.

 Both lesions are commonly CSF cystic structures.

They occur near the midline and may arise in the sutures of the calvarial vault. 

 They may extend to the skin and internally to the brain or venous sinuses. 

 Osteolytic, scalloped or eroded lesions of the skull occur with these lesions.

 The lesions are low in attenuation on CT with no internal enhancement. 

 Thin rims are present and lesions can look cystic. These lesions may be hard to distinguish from CSF.

Epidermoids have restricted diffusion on diffusion imaging. The lesions are hyperintense on T2 and PD sequences on MR imaging. Thin stalks connecting to brain or venous sinuses can be seen with high resolution MR imaging.   

  Differential diagnosis includes Langerhans’ histiocytosis and sinus pericranii. 

 An encephalocele extends as a cyst from within the calvarial vault.

A cephalohematoma is external to the vault but bounded by the bone.

A sebaceous cyst is in the differential diagnosis, but the midline position overwhelmingly favors dermoid/epidermoid.

Correct answers by users

VCU Resident
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    VCU Department of Pediatric Radiology Virginia Commonwealth University VCU Medical Center