Acute Cerebellitis-is it infectious or post infectious?

12 yr old boy had febrile episode of 5 days before developing seizures, and ataxia with altered sensorium and shows  on MRI,  an ill defined possibly” C “shaped , subtly enhancing  fluid signal intensity on all pulse sequences , of predominantly white matter regions  of posterior fossa, with more of vasogenic  rather than cytotoxic oedema ,  mass effect on 4^th ventricle, leading to  proximal hydrocephalus  and no bleed- picture suggestive of post infectious BRPINDs (Benign  Regressive  Post   Infectious Neurological  Disorders)

Teaching points by Dr MGK Murthy.  Contributors- Mr Hamid and  Mr Gupta

1.      Infectious edema  can be diagnosed by (a) short duration ,(b) gray matter as site of involvement,(c) decreased mental status  and (d) abnormal CSF, with post infectious exhibiting  opposites of these characteristics

2.      “C” shape is apparently on account of myelinating axons separating the areas of edema

3.      Post infectious demyelinating oedema is possible

4.      BRPINDs  usually exhibit good prognosis with no residual  disabilities

5.      These can be of ADEM variety where brain and cord are involved, or neuromyelitis optica where only optic nerves and cord are involved or only cerebellar variety (as in this case)

6.      MRI  is usually diagnostic  with CSF playing complementary role

7.      BRPINDs could be caused by bacterial/viral/vaccination (MMR)/drugs(arsenic, gold and sulfas etc)/Miscellaneous(herbal extracts etc)

Acute cerebellitis-MRI

Acute cerebellitis is one of the main causes of cerebellar dysfunction in children, and may be infectious, post-infectious or post-vaccination. Its aetiology is usually viral and a large number of viruses have been implicated (varicella-zoster, measles, mumps, coxsackie, Epstein-Barr, rubeola, pertussis and diphtheria, among others), although in most cases a definite aetiology remains undetermined . The cerebrospinal fluid examination may be normal or reveal pleocytosis, and the diagnosis is based mainly on clinical criteria . The disease is usually benign and self-limiting, its prognosis is habitually good, and recovery with a few or no sequelae is the usual outcome


IMAGING- It is usually bilateral,symetrical and MRI is the investigation of choice It displays predominantly graymatter and cortical signal abnormality with white matter involvement, which when it occurs is patchy and variable ,compressing the 4 th ventricle leading to obstructive proximal hydrocehalus. It is usually is low on T1 and bright on T2 and FLAIR with NO restricted diffusion(diff from acute infarction). Restricted diffusion is more common in bacterial and anerobic cerebellitis , though it can be seen in viral eiology Contrast enhancement is typically pial and along the sulcal spaces. MRS shows necrosis ,as lactate/ lipid in occassional cases

Differential diagnosis-- include acute intoxication by drugs, alcohol, tumours and demyelination (predominantly white matter involved). Lead poisoning could simulate this and so does Lhermitte-duclos (LDD)which could be differentiated by the presence of contrast enhancement and full recovery in cases of viral cerebellitis . If any surgical intervention is planned, in any caae resembling this disease ,it is worth repeating MRI after few weeks to see progress as viral cerebellitis will invariably improve.

Case by Dr MGK Murthy, Sr Consultant Radiologist.