The sixth digit of the ICD-O-3
morphology code describes the histologic grade or differentiation
of the tumor. The ICD-O-3 grade or differentiation is not
always described by pathologists for CNS tumors. When it is
not described, assign code 9 (not determined, not stated,
or not applicable). The ICD-O-3 grade or differentiation code
for non-malignant CNS tumors is always assigned code 9. This
is documented in ICD-O-3, page 30, Rule G, paragraph 1.
Other grading systems used to describe CNS tumors
are WHO grade, Kernohan grade, and St. Anne/Mayo grade.
- Kernohan's original description of a four grade system
for astrocytomas was published in 1949. It formed the basis
for the atypia,
necrosis,
vascularity,
and other factors now used in the WHO classification, although
Kernohan grades I and II became WHO grade II.
- The Ringertz classification first published in 1950 is
a three grade system where grade I is the same as the WHO
classification, but WHO grades II, III and IV are split
between Ringertz grades II and III.
- The St Anne/Mayo system from 1988 is also known by the
names of its authors, Daumas and Duport. This system is
based on four criteria--atypia, necrosis, mitosis and endothelial
proliferation.
There is a potential score of 0 - 4 in this system.
- The WHO grading system was initially published in 1979,
but was modified in 1993 and again most recently in 2000.
The WHO system includes all types of central nervous system
tumors. It is not criteria based.
WHO grades are not the same as the ICD-O-3 grade
or differentiation and are not recorded in the sixth digit
histology code data field for grade. The grade is used by
the clinician to plan treatment and predict prognosis.
The most important thing for a registrar to
understand about the WHO grade for central nervous system
tumors is that it does not parallel the ICD-O-3 grade code
in the 6th digit of the morphology code. As this graphic shows,
Grade I in the WHO system is roughly equivalent to a behavior
code of benign in ICD-O-3.
The following tables shows both WHO histologic
typing and ICD-O 6th digit Grade.
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