Pathophysiology of Astrocytoma
1) primary brain tumor dervied from astrocytes
2) wide variation in differentiation – grade 1 (astrocytoma), grade 2 (anaplastic astrocytoma), grade 3 (glioblastoma multiforme)
Signs and Symptoms
1) headaches (especially on waking)
2) vomiting
3) confusion leading to obtundation and coma
4) seizures
5) transtentorial (with fixed and dilated pupils due to CN III damage) or foramen magnum herniation
Characteristic Test Findings
Radiology –
1) poorly demarcated mass on MRI and CT scan
2) grade 3 – often crosses the midline and assumes “butterfly shpae”
3) grade 3 often with hemorrhage and frequent necrosis
Histology/Gross Pathology
Grade 1 –
1) well-differentiated astrocytes with a matrix of thin glial processes; but, grossly, tumor is poorly demarcated
2) occurs in cerebellum and midbrain in children (pilocytic subtype is cystic) and cerebrum in adults) some subtypes have Rosenthal’s fivers (thick eosinophilic fibers)
Grade 2 –
4) increasing cellular pleomorphism
Grade 3 –
5) endothelial cell proliferation in “glomeruloid” pattern
6) marked cellularity
7) serpentine areas of necrosis surrounded by “palisading” cells
8) areas of hemorrhage with red and yellow butterfly tumor
Biochemistry
1) if grade 3 tumors arise de novo, they are associated with a gene defect of amplification of epidermal growth factor receptors
2) if grade 3 tumor arises from a pre-existing grade 1 or 2, it is associated with the p53 or INK4a gene alterations
Inheritance/Epidemiology
1) life expectancy – 5 years for grade 1, 3 years for grade 2, and 9-12 months for grade 3
2) occasionally, the pilocytic subtype of grade 1 tumors can be resected for cure
3) grade 1 tumors mostly occur in children
4) grade 3 tumors are the most common intracranial primary tumor
Treatment
1) surgery for resection for cure (unlikely) or debulking
2) focused external beam radiation
3) sterotactic radiation with gamma knife
4) glucocorticoids
5) chemotherapy with nitrosureas (carmustine, lomustine)
6) many experimental therapy trials are underway with catheter based therapies
7) anecdotal reports of successful treatment with herbal and integrative medicine modalities
Tips for USMLE
1) astrocytomas almost never metastasize outside the CNS
2) if a 76 year old man with no medical problems has been having headaches every morning for the past month, now wakes up acutely confused, and has an MRI that shows a lesion in his frontal lobes in the shape of a butterfly, think glioblastoma multiforme.
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