PMC4898078_01
22-year-old man with complicated arachnoid cyst. A, Initial non-contrast axial head CT at the level of the atria of the lateral ventricles. There is a left sided subdural hematoma (yellow arrow) that is of the same attenuation as the adjacent brain parenchyma. Both mass effect and midline shift are demonstrated. B, Inferiorly, a hemorrhagic, round, extra-axial mass (green arrow) is seen in the anterior aspect of the left middle cranial fossa on non-contrast axial head CT. C, CT bone window image at the same level as Fig. 1A demonstrates scalloping of the inner table of the calvarium (green arrow).
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Initial non-contrast head CT (Fig. 1A) showed a left sided isoattenuating extra-axial collection consistent with an early subacute subdural hematoma. A lobulated mass-like appearance of extra-axial hemorrhage within the anterior aspect of the left middle cranial fossa was also noted (Fig. 1B). There was focal thinning with periosteal scalloping of both the squamous portion of the left temporal bone and of the adjacent left parietal bone (Fig. 1C).
22-year-old man with complicated arachnoid cyst. A, Axial T2-weighted MR image. The lesion is transected in the middle by the arachnoid membrane (blue arrow). Both segments (green and yellow arrows) demonstrate signal that is isointense to the adjacent brain parenchyma. B, Axial T1-weighted MR imaging better demonstrates the lesion's complex nature. The lesion represents an arachnoid cyst (green arrow) which shows evidence of hemorrhage as demonstrated by the presence of T1 shortening. The surrounding subdural hematoma (yellow arrow) shows well demarcated prominent T1 shortening indicative of hemorrhage. C, Contrast enhanced axial T1-weighted MR imaging shows enhancement of the dural membrane but does not show enhancement within the arachnoid cyst (green arrow). The arachnoid membrane (blue arrow) separates hemorrhage in the subdural compartment (yellow arrow) from hemorrhage inside the arachnoid cyst (green arrow). D, Coronal contrast enhanced T1-weighted MR imaging shows the arachnoid cyst (green arrow), arachnoid membrane (blue arrow), and subdural hematoma (yellow arrows).
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T2-weighted MR imaging (Fig. 2A) the collection had a nearly isointense signal to adjacent brain parenchyma while on T1-weighted MR imaging (Fig. 2B) the collection demonstrated increased signal intensity. These findings were consistent with early subacute hemorrhage. After contrast administration, enhancement of only the outer dural membrane but not the internal cyst structure was found on MRI (Fig. 2C). A fine linear septation, representing the arachnoid membrane, divided hemorrhage in the subdural space from hemorrhage in what was thought to be an arachnoid cyst in the middle cranial fossa (Fig. 2D).
22-year-old man with complicated arachnoid cyst. Intraoperative visualization of the subarachnoid space, arachnoid membrane, and sylvian fissure after evacuation of the subdural hematoma.
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After evacuation of the hematoma the arachnoid cyst was visualized and fenestrated (Fig. 3).
22-year-old man with complicated arachnoid cyst. Postoperative non-contrast axial head CT. The hypoattenuation in the anterior aspect of the left middle cranial fossa represents the fenestrated arachnoid cyst (green arrow). Air within the cyst reflects communication between the structure and the drained subdural hematoma.
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A decrease in extra-axial fluid and a reduction in mass effect were seen on postoperative CT (Fig. 4).