Typical Versus Atypical- What does that mean?

At one time all gliomas of the brainstem were thought to have an equally poor outcome.   Over the years (especially with better imaging), we have come to find not all brainstem gliomas are the same.—  and actually some brainstem gliomas (tectal gliomas, cervicomedullary gliomas, focal gliomas) were found to have a favorable prognosis.  However, the vast majority of brainstem gliomas- perhaps 85%- were diffuse and intrinsic and pontine.   These DIPGs, diffuse intrinsic pontine gliomas were all though to the same terrible life expectancy.

Now it has been found that not all DIPGs are the same.   Some children initially diagnosed with diffuse intrinsic pontine gliomas unexpectedly had prolonged survival.   There seems to be increasing understanding that some of these tumors are typical with the predicted short survival; then there are others that are atypical and might have longer time.

So what makes a DIPG atypical versus typical?  

 Well, there have been developing imaging appearance and clinical presentation criteria that may put a child on one side or the other. 

Typical Imaging-

1)   The tumor is diffuse without exophytic components or focality,   The tumor is mixed in through normal tissue like “sand in grass” or “pepper in jello”.

2)   The epicenter is located in the pons.  

3)   A majority of the base of the pons is affected.    Some trials require 50% while others require infiltration of 2/3 of the basis pons.

Typical Clinical Features-

1)   Age- So far seems to be written as more than 3 years of age to 18 or 21.  Younger and older patients with diffuse intrinsic pontine tumors are more likely to have prolonged survival.

2)   Clinical Symptoms Triad- Children at the time of presentation tend to have 2 out of 3 typical symptoms.   The typical triad includes a) ataxia/unbalanced gait, b) cranial nerve signs, and c) “long tract signs”- often weakness on one side.

3)   Symptom progression-Symptoms progress rapidly within one to two months from onset to diagnosis.

So, what difference does typical versus atypical make?   

Those with atypical radiographic appearance or clinical  features a may have increased survival.   This may be because these tumors are not high grade gliomas.  Thus, many DIPG trials are requiring biopsy for those children that are atypical.  If one is atypical a difference treatment course might be recommended.

It is likely better to know if a child is atypical before choosing a treatment course.   To get another opinion one can contact the DIPG Registry (http://dipgregistry.org/patients-families/second-opinion/)
or potentially contact a primary investigator of a DIPG trial (www.clinicaltrials.gov).

Note:  As we gain more understanding of diffuse intrinsic pontine tumors the categorization and definitions will probably change just as we have seen over the last couple decades.