Diagnosis under the microscope (Histological Diagnosis)
Traditionally, brain tumours have been diagnosed under the microscope. This means that a pathologist would study the tissue and classify the tumour based on how the cells appeared and behaved under the microscope. This is referred to as the histology of the tumour and refers to the histological diagnosis.
The challenge in diagnosing PNETs this way
The challenge in trying to diagnose PNETs this way is that under a microscope PNET tumours all appear to the same.
For a long time, doctors were unable to differentiate PNETs under the microscope and therefore believed that PNETs were a homogenous group of tumours (i.e.the same). This resulted in all PNETs being treated similarly.
With the development of more sophisticated ways of studying tumours through molecular profiling, doctors have discovered that PNETs are in fact a very diverse group of tumours requiring different treatment protocols.
However, if the diagnosis is based only on what is seen under the microscope, only a broad diagnosis of ‘PNET brain tumour’ can be given. Based on the new terminology adopted by the World Health Organisation, the diagnosis would officially be named ‘CNS Embryonal Tumour, Not Otherwise Specified.’