Cerebral metastases mimicking abscesses
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Two lesions are present both with peripheral ring enhancement and marked diffusion restriction (ADC -500 x 10-6 cm2/s).
The frontal lesion, on T1 sequence the lesion is isointense centrally with an intrinsically T1 hyperintense rim that enhances. There is central T2 hyperintensity, with extensive surrounding T2/ FLAIR hyperintensity in keeping with vasogenic oedema. Punctate susceptibility blooming around the periphery of the lesion. Some local mass effect is observed, with effacement of the adjacent left frontal sulci.
The second lesion is seen in the cerebellar vermis is T1 isointense and T2 hyperintense, with an enhancing rim. There is surrounding T2/FLAIR hyperintensity extending into both cerebellar hemispheres. The lesion exerts local mass- effect with distortion of the fourth ventricle, however no evidence of hydrocephalus is seen.
No further enhancing lesion is seen. There are multiple punctate foci of T2/FLAIR hyperintensity in both cerebral hemispheres, more than expected for patient age. The remainder of the brain is unremarkable.
Conclusion: Ring-enhancing lesions in the left frontal lobe and cerebellar vermis should be considered cerebral abscesses until proven otherwise. Occasionally haemorrhagic metastases can have similar appearances (e.g. melanoma, or haemorrhagic breast / lung) but in the absence of known malignancy / metastatic disease, this is considered unlikely.
The patient went on to have surgery which revealed that the lesion was a cerebral metastasis.
MICROSCOPIC DESCRIPTION: Sections of brain tissue show a cohesive tumour forming solid sheets with cells containing abundant amphophilic cytoplasm, vesicular nuclei and prominent nucleoli. Focally tumour cells form papillary structures and glands. Frequent mitoses and focal necrosis are present.
Immunohistochemical results show tumour cells stain:
CK7+, CK20-, ER- and PR-, TTF1+, NapsinA+, GATA3-, GCDFP-; HER2-, CDX2-, p63- and PAX8 focal+; consistent with primary lung adenocarcinoma.
FINAL DIAGNOSIS: Poorly differentiated adenocarcinoma presumably from lung.
Having difficulty in distinguishing metastases from cerebral metastases is frustrating, however it is better (in the setting of prominent central restricted diffusion) to err on the side of favouring abscesses.
Possibly the best clue in this case is the presence of incomplete T2 signal loss on SWI in the superior lesion (abscesses usually have a smooth complete ring) and the fact that the cerebellar lesion does not have prominent restricted diffusion. There is also a central area of more facilitated diffusion in the frontal lesion.