20 February 2017

Herpes Simplex Encephalitis

6 months old child diagnosed with Herpes Simplex Encephalitis (HSE). CT showing low density areas in both temporal lobes. This finding is difficult on CT due to artefacts often present in middle cerebral fossa. Clue here is the coronal reconstruction showing low density in the lower parts of the basal ganglia.

MR in acute phase confirms diffusion restriction bilateral in the lower parts of the basal ganglia as well as oedema seen on T2.

T2 and FLAIR show diffuse oedema in the lower parts of basal ganglia on both sides. 

Follow up MR about 3 months later showing on FLAIR and T1 extensive atrophy and gliosis in the temporal lobes. 

Axial SWI showing extensive hemorrhagic changes (hemosiderin) in the HSE damaged regions. Note extensive encephalomalacia involving temporal lobes and lower parts of basal ganglia.

Teaching point here is to have an extra careful look at CT images that are mostly performed as first line of examination, especially look for oedema and low density in both temporal lobes, lower parts of basal ganglia and the limbic system. It is recommended to perform MR study for further diagnosis. In older patients infarction is the main differential diagnosis. HSE is mostly bilateral and often asymmetric.  

05 August 2016

Epidermoid Cyst in CPA

Another classic case of epidermoid cyst in the typical location: Cerebello-Pontine-Angle (CPA). Above images show DWI restriction. Signal is lower on T2 than CSF. There is no enhancement.

Here are some other examples:
Epidermoid Cyst DWI
Epidermoid Cyst

30 March 2015

Smiling Perivascular Space

Note this enlarged perivascular space in a typical location in the lower parts of the basal ganglia. The "smiling face" represents small vessels. 

Contrast enhanced T1 shows the small vessels even better.

You can also check my other examples of Perivascular Spaces and Dilated Perivascular Spaces.

15 December 2014

Active MS plaques on DWI b1000

MS plaques showing highest signal on b1000 are most suspect for activity - in my opinion. Therefore look at DWI (b1000) when reporting brain MRI of MS patients. 

Note the largest MS plaque (FLAIR left image) that shows typical peripheral enhancement (T1 C+ right image). You can also see other smaller plaques that do not enhance. 

Now observe that this plaque, unlike other, has high signal on b1000 (left image), without restriction on ADC (right image). Other plaques do not show such high signal on b1000. 

My point is that b1000 gives a clue to active plaques

06 April 2013

Orbital Cavernous Hemangioma MRI

Note well defined strongly enhancing mass located medially in the right orbit. This extraconal mass has high signal on T2. It has not changed over time. This is Orbital Cavernous Hemangioma. If we would perform dynamic contrast scan it would show graduate enhancement. Here is the mass nicely depicted on T2, T1 FS with contrast and on CT. Case is complementary to my previous case.