This Japanese article electronically published in Childs Nervous System makes the case that although MRIs have been the basis for diagnosis for DIPGs since the 1990s, "the accuracy of MR imaging baded diagnosis has not been fully confirmed". This article goes on to say that there have been several reports indicating that some of these diffuse intrinsic brainstem lesions have been found to be other tumors rather than gliomas. These have included PNETs, ependymomas, gagliogliomas, rhabdoid tumors and pilocytic astroctyomas. These other pathologies have been particularly found in those tumors that have an atypical appearance.
The authors decided to perform biopsy for pediatric intrinsic pontine lesions with atypical for DIPG findings on MRI. Atypical MRI findings were defined as:
a) extended beyond the pons
b) had a well-defined, localized enhancing part with in a high intensity lesion on T2-weighted images.
Seven patients underwent open biopsy because of diffuse lesions in the pons that were not typical for DIPG. Four patients had a focal enhancing lesion, five had extension beyond the pons and two had both.
The biopsy revealed:
5- diffuse brainstem glioma
1- PNET
1-pilocytic astrocytoma
There were no biopsy related deaths or intra-operative complications. One child has transient worsening of hemiparesis.
The 12 year-old child harboring a PNET presented with double vision, unsteady gait and a facial palsy. His tumor had focal enhancement but no extension beyond the pons. The child received craniospinal radiation with tumor boost and chemotherapy as would be done for a supratentorial PNET with marked shrinkage. At 13 months the tumor recurred near the genu of the corpus collosum. This lesion had radiosurgery.
The 7 year old female with a pilocytic astrocytoma presented with difficulty speaking. Her tumor did not enhance but extended beyond the pons into the right cerebellar peduncle and pons. She did not have radiation but rather carboplatin and vincristine. At the time of article submission the tumor had been stable for 9 month.
So, of the 5 children found to have high grade gliomas three of these had areas of focal enhancement and four had extension outside the pons. The presenting symptoms included only right hemiparesis in one, only a facial palsy in one and lethargy in one. Only two children had 2 symptoms of the typical triad. One child had gait disturbance and facial palsy and the other had gait disturbance and hemiparesis. Of these 5 high-grade glioma children, four of the tumors regrew within 7months( range 3-7 months). Two of these children had died at the time of publication.
From this very small sample it seems there is no way to predict by MRI pathology without biopsy in atypical diffuse pontine tumors. The article concluded that "an open biopsy of intrinsic brainstem lesions is considered safe and effective for selecting appropriate course of therapy".
References:
The efficacy of biopsy of intrinsic brainstem lesions for decision making of treatment.Childs Nerv Syst. 2013 Feb 3. [Epub ahead of print]
http://www.ncbi.nlm.nih.gov/pubmed/23377758
