Classification of pituitary adenoma

The classification is based on the three following characteristics:

1: tumour diameter into micro (<10 mm), macro (≥10 mm) and giant (>40 mm) by MRI

2: tumour type into GH, PRL, ACTH, FSH/LH and TSH by immunocytochemistry

3: tumour grade based on the following criteria:

 Invasion defined as histological and/or radiological (MRI) signs of cavernous or sphenoid sinus invasion

 Proliferation considered on the presence of at least two of the three criteria:

  Ki-67: >1 % (Bouin-Hollande fixative) or ≥3 % (formalin fixative)

  Mitoses: n >2/10 HPF

  P53: positive (>10 strongly positive nuclei/10 HPF)

The five grades are the following:

 Grade 1a: non-invasive tumour

 Grade 1b: non-invasive and proliferative tumour

 Grade 2a: invasive tumour

 Grade 2b: invasive and proliferative tumour

 Grade 3: metastatic tumour (cerebrospinal or systemic metastases)¹