Unusual sigmoid sinus lesion

A 10 yo male with right retro mastoid pain.  

Here are his MRI Brain images with non contrast 3 D TOF MR Angiogram, non contrast 2 D TOF  MR Venogram as well as axial CT sections with bone window images. 

Findings:
A well demarcated round to ovoid lesion in right sigmoid sulcus in the region of sigmoid sinus.
On MRI, a thin low signal intensity rim at the periphery on all pulse sequences, faintly getting hyperintense at the center on T2 and FLAIR images. Signals are low on T2*GRE. Lesion show intense homogeneous enhancement on post contrast T1.
Mild indentation over adjacent right cerebellum. No parenchymal invasion or perilesional odema.
No flow related signals in the region of right lateral sinus on MR Venogram.
MR Angiogram normal.
On CT, lesion is uniformly isodense with a thin hyperdense rim of uniform thickness at periphery. Bone window show no abnormal bone destruction or scalloping of adjacent bony sigmoid sulcus. Right mastoid air cells show normal pneumatisation.

Imaging wise i feel its a sigmoid sinus varix with thrombus in it.

Explanation:
Lesion is seen in sigmod sulcus in the region of sinus, no separate sigmoid sinus seen adjacent to this lesion, in consecutive sections lesion appears to be in continuity with transverse sinus so it seems to be the lesion related to sigmoid sinus itself. On CT uniform thickness hyperdense rim seem to be the normal dural outline around the abnormal focal aneurismal dilatation of right sigmoid sinus. Thrombus / blood clot in this aneurysmally dilated portion of sinus show low signal intensity on T2 and FLAIR with isointense signal on T1, lesion is isodense on CT. Enhancing thrombus on post contrast T1w images. Right lateral sinus non visualised on MR Venogram being thrombosed.