Central neurocytoma

There is a large mass in the left ventricle comprising soft tissue, cystic foci of CSF density, and coarse linear/serpentine calcifications. The soft tissue component barely enhances post-contrast. The mass extends a soft tissue tendril though the foramen of Monro into the third ventricle. There is marked obstructive hydrocephalus, with leftward bowing of the septum pellucidum. Pronounced mass effect, manifesting as diffuse effacement of the sulci and basal cisterns, and bilateral tonsillar herniation.

The differential diagnosis is mainly of central neurocytoma or ependymoma (less likely, given the location).

VP shunt via right frontal approach, its tip in the right ventricle, with small amount of intraventricular air. Marked dilatation of the lateral and third ventricles, small amount of blood in the occipital horns. Merely mild transependymal edema around the occipital horns, more on the right. The fourth ventricle is narrowed more than expected.

Large cystic-solid mass centered in the body of the left ventricle, passes through the foramen of Monro, involves the third ventricle and extends to the opening of the Sylvian aqueduct.

The mass has a broad base on the septum pellucidum and on the lateral border of the ventricle and bulges toward the right ventricle. The dimensions of its central portion are 45 x 32 x 60 mm. 

The mass exhibits a very heterogeneous signal on the T1W and T2W sequences, with flow voids, calcifications and foci of intratumoral hemorrhage. There are solid components, e.g. in its superior part, that show diffusion restriction. It contains well-developed blood vessels. There is minimal post-contrast enhancement. Calcific stripe along the lateral border of the left ventricle.

At MRS at TE=135, there is a low NAA peak, high choline peak, inversion of the choline:creatine ratio, and a lactate peak.

At perfusion, there is hyperperfusion.

The mass and the resultant hydrocephalus elicit a substantial mass effect, with diffuse sulcal narrowing, slightly less than on the pre-shunt CT study. The septum pellucidum now deviates slightly to the right and the corpus callosum is displaced and narrowed. There is a mass effect in the posterior fossa as well, manifesting as narrowing of the basal cisterns, mild narrowing of the fourth ventricle, and marked bilateral tonsillar herniation.

Bilateral distended optic nerve sheath complex with papilledema.

No evidence of peritumoral edema. No evidence of additional masses. No evidence of cranial nerve enhancement. No abnormal focal parenchymal findings. No evidence of infarction or acute intracranial parenchymal hemorrhage.

Smooth, diffuse sulcal hyperintensity on post-contrast FLAIR, possibly due to sulcal effacement and vascular enhancement.

Normal flow signal in the venous sinuses. Bilateral focal circular filling defects at the transition between the transverse and sigmoid sinuses, most probably arachnoid granulations. Normal flow signal from the large cerebral arteries. 

Mucosal thickening and enhancement in the paranasal sinuses, with a small amount of fluid in the left maxillary sinus, compatible with sinusitis. The mastoid air cells are well aerated.

In summary:

Large mass in the left ventricle, extending into the third ventricle, with a broad base on the septum pellucidum and a heterogeneous pattern, including multiple cystic areas, solid foci, calcifications, flow voids, and foci of hemorrhage. Central neurocytoma is first on the differential list, while other intraventricular masses are possible but less likely.
Marked hydrocephalus, with substantial supratentorial and infratentorial mass effect, despite the presence of a VP shunt.