Diffuse Intrinsic Pontine Glioma

Location


The pons is an approximately 2cm long "knob-like" process located deep in the middle of the brain.

One can visualize the pons as a box...
Top - midbrain
Bottom - medulla
Front - pontine cistern and the clivus (the slanted bony bottom part of the skull)
Back - 4th ventricle.
Sides - Cerebellar Penduncles


Contents


The pons itself is divided into a back (medically called dorsal) part and a front (medically called ventral) part. The back part is often called the pontine tegmentum whereas the front part is called the ventral or basal pons. There are 4 paired cranial nerves (one on the left and one on the right) that start in the pons.


Cranial Nerves


The cranial nerves are nerves that control the special senses and the movement/sensation of the head and neck. Four sets of cranial nerves come from the pons.

5th - Trigeminal nerve
6th - Abducens nerve
7th - Facial nerve
8th - Vestibulocochlear nerve


Pontine Tegmentum


The pontine tegmentum is against the 4th ventricle and contains an origin of 4 cranial nerve (5th, 6th, 7th and 8th nerve), the reticular activating system, ascending/descending nerve tracts as well as other nuclei.



Ventral Pons


The ventral pons consists of nerve fibers tracts going up and down as well as across the area.  It acts as a massive relay station connecting the cerebral cortex to the cerebellum on the other side through a structure called the cerebellar peduncles.



Cerebellar Peduncles


The cerebellar peducles (also called brachium pontis) are the nerve superhighway from the pons to the cerebellum.  It is interesting to note that both the cerebellum and the pons share the same developmental seed as the embryonic metencephalon.



Microscopic Cross Section of the Pons


The area above the blue is the tegementum.
The area below the blue is the ventral pons.
The crossing fibers in the vental pons continue to the sides to form the cerebellar peduncles.



Blood Supply


The blood to the pons is supplied by the pontine arteries. These are small arties that branch off the basilar artery.



Used with permission from Just One More Day

Different Brainstem Glioma Locations


A- tectal glioma
B- focal midbrain tumor
C- focal intrinsic pontine glioma
D- doral/exophytic glioma
E- Diffuse Intrinsic Pontine Glioma
F- focal medullary glioma
G- cervicomedullary glioma

From Dr Ken Cohen's slides from the April 2009 FDA meeting.
www.fda.gov

This slide is from the top of page 7. MRIs and pathologic specimens of DIPGs (letter E) are on the prior pages.

Minutes of the Meeting- www.fda.gov
The above slide discussion is on page 34 line 20 to page 35 18.



---------excerpted from transcript---------

"so again, just to make the point here, that what we are talking about is this lesion, here, is this lesion that's describe as E. So none of the other lesions that we are thinking about, here, really have anything to do with the lesion that is I specifically related to the morbidity, mortality that I described previously.

Almost all these other lesions, if they are biopsied, many of them will be pilocytic astrocytomas. Occassionally, you'll see a fibrillary astrocytoma, but the natural history is quite different. So, it's really this diffusely infiltrating lesion of the pons.

There are times when the imaging isn't quite so clear and in those circumstances where it is not quite certain whether this really represents E versus maybe an extension of D-type lesion. In those cases, I would say, in general, biopsy is recommended, and it is really in those – that case-- that we use this for diagnostic purposes."