User:DerekvG/sandbox/braintumor/astrocytoma

Grading
Of numerous grading systems in use for the classification of tumor of the central nervous system, the World Health Organization (WHO) grading system is commonly used for astrocytoma. Established in 1993 in an effort to eliminate confusion regarding diagnoses, the WHO system established a four-tiered histologic grading guideline for astrocytomas that assigns a grade from 1 to 4, with 1 being the least aggressive and 4 being the most aggressive.

The WHO-grading scheme is based on the appearance of certain characteristics: atypia, mitosis, endothelial proliferation, and necrosis. These features reflect the malignant potential of the tumor in terms of invasion and growth rate. Tumors without any of these features are grade I, and those with one of these features (usually atypia) are grade II. Tumors with 2 criteria and tumors with 3 or 4 criteria are WHO grades III and IV, respectively. Thus, the low-grade group of astrocytomas are grades I and II.

Various types of astrocytomas are given these WHO grades:

According to the WHO data the lowest grade astrocytomas (grade I) make up only 2% of recorded astrocytomas, grade II 8%, the higher grade anaplastic astrocytomas (grade III) make up 20% of recorded astrocytomas. Finaly the highest graded astrocytoma gradeIV GBM is the most common primary Cancer of the Nervous System and second most frequent brain tumor. Despite the low incidence of astrocytomas compared to other human cancers, mortality is significant, as the higher grades (III & IV) present high mortality rates (mainly due to late detection of the neoplasm).

== Infiltrating low-grade astrocytomas grow slowly compared to their malignant counterparts. Doubling time for low-grade astrocytomas is estimated at 4 times that of anaplastic astrocytomas. Several years often intervene between the initial symptoms and the establishment of a diagnosis of low-grade astrocytoma. One recent series estimated the interval to be approximately 3.5 years. The clinical course is marked by a gradual deterioration in half of cases, a stepwise decline in one third of cases, and a sudden deterioration in 15% of cases. Seizures, often generalized, are the initial presenting symptom in about half of patients with low-grade astrocytoma.

For patients with anaplastic astrocytomas,3 the growth rate and interval between onset of symptoms and diagnosis is intermediate between low-grade astrocytomas and glioblastomas. Although highly variable, a mean interval of approximately 1.5-2 years between onset of symptoms and diagnosis is frequently reported. Compared to low-grade lesions, seizures are less common among patients with anaplastic astrocytomas. Initial presenting symptoms most commonly are headache, depressed mental status, and focal neurological deficits. ===