This 19 year-old G₂P₁ patient was seen for a routine anatomy survey examination at 17 weeks. Selected images of her examination are provided below and in a 2.6 MB MPEG video-clip as well as a 4.7 MB video-clip. Some users have problems playing MPEG clips. If this is your case select the second (larger) clip. The content of both clips is identical.

This was a case for which the finding was simple to recognize, but the identification caused some problems.

Findings

• The obvious finding is that there is a small cystic structure in the anterior-superior aspect of the skull.
• Less obvious, but well demonstrated on the video-clip was that the cyst is not communicating with the ventricles or even with the subarachnoid space.
• Further neither the ventricles nor the subarachnoid space is abnormal.
• No particular vessel was seen in proximity to the cyst.

Diagnosis

The most tempting diagnosis when finding a cystic structure around the skull and in particular in this position is a frontal cephalocele. However, with normal ventricles and mostly with a complete separation between the cyst and the brain, the diagnosis is quite unlikely. I had tried to alert to the fact that this was not the obvious diagnosis by reminding to “not shoot from the hip”.

Other diagnoses that were submit included:

• extracranial arachnoid cysts (no such condition in Medline)
• leptomeningeal cyst (usually post birth trauma)
• cephalhematoma or subgaleal hemorrhage (also usually post birth trauma)
• intra- and extracranial arteriovenous communications (rare and no visible Doppler signal)
• hemangioma (not the correct texture, see the other cases posted of hemangioma)

Several cysts have also been suggested, but of those the most typical is an epidermal scalp cyst.

This was confirmed postnatally:

Sagittal view over the cyst

Transverse views (note the interhemispheric fissure). Also in the energy and velocity Doppler image note flow in the superior sagittal sinus.

And the cute little girl:

Epidermal scalp cyst.