Findings:
Large mass measuring 125 x 75 x 81 mm located at the left anterior and middle cranial fossae with extensive mass effect on the adjacent brain parenchyma, basal ganglia and the midbrain. Consequential compression of the left lateral ventricle and enlargement of the right lateral ventricle and the posterior horn of the left lateral ventricle. Mild transependymal and periventricular edema on the right. There is marked midline shift to the right (up to 1.5 cm).
The mass extends to the right frontal region. Anteriorly the lesion extends to the left frontal sinus through a bony defect at the posterior wall of the left frontal sinus, measuring approximately 7 mm.
The lesion appears to extend into the temporal horn of the left lateral ventricle, which shows a downward glide across the tentorial incisura compressing the brainstem in the ambient cistern on the left.
The lesion demonstrates heterogeneous low T1 and high T2 signal intensities, with diffusion restriction. On the postcontrast study minimal peripheral linear enhancement is seen, which likely reflects displaced adjacent vessels. Mild surrounding perifocal oedema is seen adjacent to the posterior border of the tumour.
The orbits are unremarkable. Mild mucosal thickening is noted in the paranasal sinuses bilaterally. Partial obliteration of the mastoid air cells is seen on both sides.
Previous left frontal cranioplasty is noted.
Conclusion:
Large intracranial, extra-axial mass lesion in the left anterior and middle cranial fossae, extending into the right frontal region, into the left temporal horn and into the left frontal sinus. The features are characteristic of an intracranial epidermoid tumour.
Associated, extensive mass effect with isolated right ventricular hydrocephalus and left uncal herniation.