= venous anomaly (? subperiosteal venous angioma)

= collection of abnormal nonmuscular scalp veins adherent to skull (= dilated subperiosteal epicranial venous structure) connected to intracranial venous system (sinus / cortical vein) by anomalous diploic veins through a well-defined calvarial defect

Etiology: congenital; ? traumatic

Age: childhood; M = F

• focal soft painless scalp mass that reduces under compression
• headache, scalp pressure, pain (rare)

Location: frontal + parietal bone

• calvarial thinning + defect
• mild ↓ / mild ↑ / no change in size over time

CT:

• sessile sharply marginated homogeneous densely enhancing mass adjacent to outer table of skull
• transcalvarial perforating channels
• connection to adjacent dural venous sinus
• possible drainage into extracranial scalp veins

Angio:

• extracalvarial sinus may not opacify ← slow flow

Rx: ligation of communicating veins + removal of sinus; endovascular embolization

DDx: cephalocele, hemangioma, dermoid cyst, calvarial metastasis