This video is the sixth video in an overview about the emergent approach to brain tumor imaging. This video talks about some of the common mimics for things that look like tumors. The most common diagnoses you need to be aware of are infection, abscess, and demyelination.
This case shows a CT in a patient that has hypodensity in the left medial temporal lobe. It is ill-defined and not well marginated. On CT, the differential is an acute encephalitis and tumor. Stroke is less likely given that it isn’t in a vascular distribution and doesn’t have the right clinical onset. The MRI shows really apparent swelling and edema/hyperintensity on T2 and FLAIR. Diffusion is also hyperintense. On post-contrast imaging, there is avid and solid nodular and ill-defined enhancement.
Herpes encephalitis is a dreaded intracranial infection that requires urgent recognition and treatment. It can be unilateral or bilateral, and is often asymmetric. Red flags include temporal involvement, acute clinical signs of illness, and not following a vascular distribution. These patients may have rapid progression. If no cause is found via clinical workup or lumbar puncture, these patients should get a follow-up in 6-12 weeks to ensure that it is improve and is not a tumor.
This case has a CT which shows marked edema in the left frontal lobe with a mass in the left frontal lobe adjacent to the frontal horn. It looks like the mass is peripherally hyperdense but hypodense centrally. It is not following a vascular distribution. Your differential diagnosis includes tumors, both primary tumors and metastatic disease. An MRI and systemic work-up for malignancy are justified. The MRI shows a mass with peripheral T2 hyperintensity and small areas of susceptibility which are probably blood products. On post-contrast imaging, the periphery is avidly enhancing with blurry margins. The DWI images are key and show pretty marked central diffusion hyperintensity which is dark on ADC.
This is a case of intracranial abscess. Brain abscesses are areas of pus and infection within the brain which have central diffusion restriction. Sometimes there are thinner along the ventricular margin. In many ways they can mimic tumors, but the central DWI hyperintensity which is “light-bulb” bright is a huge clue that you should suspect abscess. Red flags that should make you suspect infection are immune compromised patient, systemic signs of infection, rapid onset, and severe symptoms.
This patient has a CT which looks somewhat similar to the previous patient. There is a marked area of edema with sparing of the cortex in the left parietal lobe. There is no clear central mass that you see there, but given that it is vasogenic edema and there is mass effect you should be pretty suspicious. Your initial differential includes primary tumor and metastatic disease, but you want to see the MRI. The MRI shows a marked area of FLAIR and T2 hyperintensity. The area is markedly T1 hypointense but has heterogeneous and incomplete enhancement around the rim.
Tumefactive demyelination is associated with patients who have other demyelinating disease. In many cases, it’s going to be indistinguishable from tumor, but clues are sudden onset of symptoms and young age of the patient. Imaging features to look for are that incomplete rim of enhancement around the margin and the leading edge of abnormal diffusion.
When approaching a case that seems like a tumor, you have to remember that there are lesions that can mimic tumors. Systemic signs or clinical features can help you, but it can be particularly hard on CT alone. The next step is to get an MRI and work the patients up for their systemic features.