Purpose or Case Report: An 8-week-old male, born without complication at 33 weeks gestation age, presented with an undifferentiated posterior-midline scalp mass that had been present since birth. According to the mother, the mass has progressively increased in size with subjective tenderness to palpation. The mother reported possibly relevant two seizure-like episodes around 5 weeks of age consisting of jerking leg movements and staring spells with rapid blinking. Otherwise, the infant was healthy without any documented past medical or surgical history. Based on the presentation, a dedicated sonogram of the head was ordered with the goal of visualizing the mass and underlying cranial anatomy. The mass was demonstrated to be extracranial with avid vascularity. A few images raised suspicion for a trans-osseous vascular connection between the mass to the sub-adjacent dural venous sinuses. Subsequent contrast enhanced MRI and MRV imaging was ordered to distinguish the leading differential of Sinus Pericranii and Atretic Parietal Cephalocele. On MRI, the highly vascular extracranial mass demonstrated enhancement pattern similar to the dural venous sinuses. A trans-ossoeus vascular channel was seen arising from the mass coursing intracranially and communicating with the superior sagittal sinus. No arterial channel was visualized. No evidence of a persistent falcine venous sinus, primitive falcine vein or CSF tract was visualized. Subsequently, the diagnosis of Sinus Pericranii was established.

Sinus Pericranii and Atretic Parietal Cephalocele are extracranial subscapular masses that present similarly on physical examination and overall presentation. Sinus Pericranii is a low flow vascular malformation with an abnormal connection to the dural sinuses. Atretic parietal cephaloceles are small subscapular lesions with dura, dysplastic brain and fibrous tissue associated with variant intracranial anatomy including a persistent falcine venous sinus/primitive vein and/or abnormal CSF tract. Subsequently imaging findings are essential in distinguishing between the two entities and arriving at a definitive diagnosis. The presented case demonstrates this scenario.
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