Monday 19 September 2011

Anaplastic Astrocytoma MRI

MRI Brain 
Sequences planned FLAIR, T2 , DWI, T2*GRE, T1W PC.
Single voxel MRS at short TE of 35ms.  
This MRI study of Brain shows:
An ill defined right insular focal parenchymal swelling, hyper intense on T2 and FLAIR with low signal on T1, a patchy enhancement on post contrast T1.
No dense dystrophic calcification or hemosiderin staining on T2*GRE.
Mild compression over right lateral ventricle.
No significant mass effect or mid line shift.
On MR Spectroscopy, markedly reduced NAA and Creatinine, raised choline.

Imaging findings are typical of Anplastic astrocytoma.

Anaplastic Astrocytoma

Syn: WHO Grade III astrocytoma - intermediate between low grade (diffuse) astrocytoma (WHO grade II) and GBM (grade IV),  Malignant astrocytoma, High grade astrocytoma.
Definition: A diffusely infiltrating astrocytoma, focal or diffuse anaplasia and marked proliferative potential.

AA contributes ~ 1/3 of all astrocytomas and ~ 25% of Gliomas.

Imaging wise diagnostic clues is an ill defined hemispheric white matter mass. May appear well circumscribed. Variable enhancement, typically none; may be focal or patchy. Commonly involve hemispheric WM, frontal and temporal lobes. In children, may involve Pons, thalamus and less commonly involves brain stern, spinal cord.

On CT, low density ill defined mass. Calcification and hemorrhage rare. Majority do not enhance. Enhancement may be focal, patchy and heterogeneous. If peripheral enhancement, consider malignant progression to GBM.
TlWI : Mixed isointense to hypointense WM mass. Areas of hemorrhage rare may appear bright on T1.
T2WI and FLAIR : Heterogeneously hyperintense, infiltrates adjacent brain. Involve and expand overlying cortex.
DWI: No diffusion restriction is typical.
T1 PC : Usually no enhancement. Less commonly focal patchy enhancement. Peripheral enhancement suggest GBM.
MRS: Elevated Cho/Cr ratio, decreased NAA

AA has histologic and imaging characteristics along spectrum between low grade astrocytoma and GBM.

Histopathological findings
Gross features are an infiltrating mass with poorly delineated margins, often expands invaded structures. May appear discrete but tumor always infiltrates adjacent brain.
Microscopic Features characterized by increased cellularity, marked mitotic activity, distinct nuclear atypia, High nuclear/cytoplasmic ratio, Nuclear/cytoplasmic pleomorphism, Coarse nuclear chromatin, No necrosis or microvascular proliferation. Immunohistochemistry: GFAP+ common, MIB-1: 5-10% (proliferation index)

Differential diagnosis
- Low grade glioma
Focal or diffuse white matter mass.
Typically non enhancing hemispheric mass
Indistinguishable without biopsy
- Glioblastoma multiforme (GBM)
Characterized by areas of necrosis and hemorrhages, enhancing rim.
Extensive surrounding T2/FLAIR signal
- Cerebritis
T2 hyper intensity and patchy enhancement
Diffusion restriction typical.
- Ischemia
Often wedge-shaped, involves GM & WM, area of involvement corresponds to vascular territory.
Restricted diffusion if acute/subacute stage of infarction.
Gyriform enhancement in sub acute ischemia.
- Oligodendroglioma
A focal cortical mass with variable enhancement.
Dense calcification common.
May be indistinguishable.

Clinical Presentation
Occurs at all ages, most common 40-50 years, M:F = 1.8:1
Signs and symptoms varies with location.
Seizures, focal neurologic deficit common. May have headache, drowsiness, vomiting.
Increased intracranial pressure.
Personality or behavioral changes.

Resection and radiation therapy, +/- chemotherapy.

Reference: Anne G Osborn, Diagnostic imaging I-6.

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