IS Case 143: Glioblastoma Multiforme
Imaging Sciences URMC 2008
Publication Date: 2009-05-21
A 51-year old male presented with right facial droop and right upper extremity weakness in the setting of history of laryngeal cancer and HIV. A mass lesion was detected on CT. MRI demonstrated a heterogeneously enhancing mass lesion in the left frontal lobe and basal ganglia with cystic areas and significantly increased choline with minimal or mild perilesional edema. The diagnostic considerations included laryngeal cancer metastasis, lymphoma, or toxoplasma. Thallium SPECT was requested.
SPECT images after 4 mCi of Tl-201 thallous chloride demonstrate an area of increased radiotracer uptake with slightly more than twice count rate of the contralateral side. It corresponds to the left frontal lesion seen on the MRI. Similar, but slightly less intense uptake is seen in the left basal ganglia region, corresponding to the lesion seen on the MRI in that area. The radiotracer uptake is suggestive of disruption of the blood brain barrier. This is consistent with neoplastic etiology of the lesions.
Thallium-201 can be used for evaluation of the CNS lesions. In our institution the most common use is to differentiate lesions due to lymphoma versus toxoplasmosis in AIDS patients. The reported incidence is 30% versus 60% respectively. The remaining 10% are comprised by atypical infections and other etiologies. The importance of this examination is explained by ability to avoid 2-3 weeks of empiric anti-toxoplasma therapy prior to treatment of CNS lymphoma. The study is based on the fact that CNS tumors disrupt blood brain barrier and demonstrate uptake of thallium, while toxoplasmosis does not. Similar uptake is seen with F18-FDG and Tc-99m sestamibi.
In case of glioblastoma, literature suggests that degree of uptake is proportional to the malignant grade of tumor, a very important prognostic factor. Thallium can also be used to distinguish residual or recurrent tumor from post radiation necrosis and fibrosis.
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