Cerebellar metastasis - adenocarcinoma lung

There is a mass in the periphery of the left cerebellar hemisphere. This has a hyperdense rim the non-contrast images. The entire mass enhances however there is more vivid enhancement peripherally. There is extensive surrounding vasogenic edema with mass effect resulting in partial effacement of the 4th ventricle. There is hydrocephalus with dilatation of the temporal horns. No tonsillar herniation. The adjacent left transverse sinuses opacities normally. The mastoid air cells and paranasal sinuses are clear.

Chest: There is a large right upper paratracheal mass that is heterogeneously enhancing with hypodense regions medially. The enhancing component has spiculated margins extending to the pleural surfaces. No destruction of the adjacent ribs or vertebrae. Hypodense right hilar lymph node. No other mediastinal, hilar or axillary lymphadenopathy.

Biapical paraseptal and centrilobular emphysema. Mild left sided pleural thickening predominately posteriorly and basally with some nodular regions. High-density pleural thickening at the left apex with thin linear calcifications. 

Conclusion: Enhancing right paratracheal mass with regions of low attenuation. This may either represent a conglomerate of lymph nodes or alternatively a primary lung mass with adjacent lymphadenopathy. Given the central low-density tuberculosis needs to be considered. Note is made of emphysematous changes suggestive of a smoking history. 

A ring enhancing left cerebellar hemisphere lesion, which is favored to be intra-axial is T1 hypointense, and T2 hypointense to grey matter. In addition to the rim of contrast enhancement, it contains 2 central enhancing nodules. Faint susceptibility artefact is present in its rim, but there is no diffuse susceptibility blooming to suggest internal hemorrhage. The lesion demonstrates diffusion restriction (ADC = 600 x 10^-6 mm2/s), corresponding to the non-enhancing central content rather than enhancing rim and nodules. MR spectroscopy demonstrates an elevated lactate peak, with reversal of the choline:creatine ratio. 

It causes significant adjacent T2/FLAIR hyperintensity, consistent with vasogenic edema. There is mass effect with compression of the fourth ventricle/cerebellar vermis and rightward deviation of the superior medullary velum. The lateral and third ventricles are slightly larger than expected for age, suggesting mild obstructive hydrocephalus.

Conclusion: Ring-enhancing 2cm left cerebellar mass with posterior fossa mass effect resulting in mild obstructive hydrocephalus, in the context of a right upper lobe and paratracheal nodal complex conglomerate mass. The presence of diffusion restriction in the non-enhancing or poorly enhancing internal portion of the mass raises suspicion for cerebral abscess (including tuberculous), the morphologic appearance is not entirely classic and occasionally the contents of a metastasis can demonstrate restricted diffusion.