Arachnoid granulations (Pacchionian granulation) are present in the superior sagittal sinus, transverse sinus, cavernous sinus, superior petrosal sinus, and straight sinus in decreasing order of frequency 1.
Arachnoid granulations produce well-deﬁned focal ﬁlling defects within the dural venous sinuses and measure 2–9 mm in diameter 1. Occasionally arachnoid granulations can exceed 1 cm in diameter. It is important to distinguish these benign “giant” arachnoid granulations from more serious dural venous sinus pathology such as thrombosis and neoplasia to avoid unnecessary invasive procedures 2.
Arachnoid granulations produce well-deﬁned focal ﬁlling defects within the dural venous sinuses. They are isoattenuating (one-third) or hypoattenuating (two-thirds) relative to brain parenchyma on unenhanced CT 1.
Dural sinus thrombosis usually involves an entire segment of a sinus or multiple sinuses and can extend to cortical veins and show homogenous hyperdensity on unenhanced CT whereas arachnoid granulations produce focal, well-defined nodular defects in the sinuses and are never hyperdense on CT or hyperdense on T1WI 3.
The typical MRI findings of dural sinus thrombosis are an iso- to hyperintense blood clot in the sinus on T1WI which is hyperintense on T2WI 3.
The key MRI features of giant arachnoid granulations are non-enhancing granules with central linear enhancement and surrounding enhancing flowing blood on contrast-enhanced MR venography 3.