Case Author(s): Dennis Hsueh, M.D. and Barry A. Siegel, M.D. , 04/05/04 . Rating: #D2, #Q3

Diagnosis: Recurrent right frontotemporal anaplastic astrocytoma

Brief history:

40-year-old man with a history of a right frontal lobe anaplastic astrocytoma treated with a partial resection followed by radiation therapy. He underwent a second surgical resection of residual tumor, with concomitant chemotherapy, 6 months later.

Images:

Axial and coronal FDG-PET brain images

View main image(pt) in a separate image viewer

View second image(mr). Selected T1-weighted pre -and post-gadolinum axial MR images of the brain.

View third image(pt). Selected T1-weighted post-gadolinum axial MR images with corresponding fused and PET axial images

View fourth image(pt). Selected T1-weighted post-gadolinum coronal MR images with corresponding fused and PET coronal images

Full history/Diagnosis is available below

Diagnosis: Recurrent right frontotemporal anaplastic astrocytoma

Full history:

40-year-old man with a history of a right frontal lobe anaplastic astrocytoma treated with a partial resection followed by radiation therapy. He underwent a second surgical resection of residual tumor, with concomitant chemotherapy, 6 months later.

Radiopharmaceutical:

F-18 Fluorodeoxyglucose(FDG) i.v.

Findings:

MRI: Selected images demonstrate an enhancing mass in the right inferior frontal lobe and anterior right temporal lobectomy site.

PET: There is generalized mild decrease in FDG uptake in the right cerebral hemisphere suggesting edema and/or post-radiation effect. There is decreased FDG uptake in the contralateral left cerebellar hemisphere, consistent with crossed cerebellar diaschisis. There is increased FDG uptake corresponding to the abnormal enhancing masses in the right anterior and inferior frontal lobe, anterior to the frontal horn of the lateral ventricle and anterior to the right temporal lobectomy surgical bed. There is enlargement of the lateral and third ventricle consistent with hydrocephalus.

Discussion:

FDG-PET imaging of the brain can be challenging because of the high "background" activity in normal gray matter. High-grade malignant brain tumors typically have increased FDG uptake. Thus, FDG-PET may be helpful in determining the extent of these lesions and in assessing prognosis (which is generally worst with the most hypermetabolic tumors).

FDG-PET can also assist in defining the most metabolically active sites for stereotactic biopsy. Coregistration of the MRI and FDG-PET images is essential for accurate evaluation and localization of brain tumors.

FDG PET has also been demonstrated to be useful in distinguishing between recurrent high-grade tumor and radiation necrosis. In this case, there is relatively low background cortical activity in the right frontotemporal region, as a result of edema or post-radiation effect. This facilitates detection of recurrent high grade tumor.

With low-grade brain tumors, FDG-PET has limited value in defining extent of tumor involvement and recurrence.

Positron-emitting amino acids, such as C-11 methionine, have demonstrated accumulation in brain tumors and have the advantage of low background cortical activity. The relationship between degree of C-11 methionine uptake and tumor grade is not established.

REFERENCES

Benard F, Romsa J, Hustinx R. Imaging gliomas with positron emission tomography and single-photon emission computed tomography. Semin Nucl Med. 2003; 33:148-62.

Wong TZ, van der Westhuizen GJ, Coleman RE. Positron emission tomography imaging of brain tumors. Neuroimaging Clin N Am. 2002; 12:615-26

Followup:

Follow-up MR images 2 months after PET: There is enlargement of the enhancing mass in the anterior temporal lobe surgical bed consistent with tumor recurrence. Also, there are enhancing masses in the anterior corpus callosum, left uncus and left inferior frontal lobe consistent with metastastic foci. Since the corpus callosal tumor does not cross midline, the left-sided lesions are presumed to represent subarachnoid seeding of tumor. There is increased subependymal enhancement around the right lateral ventricle consistent with subependymal tumor spread.

View followup image(mr). Selected T1-weighted post-gadolinum axial MR images. Top 8 images: Obtained concominantly as the above PET examination. Bottom 8 images: Obtained 2 months after the PET examination.

Major teaching point(s):

1. FDG-PET is useful in distinguishing between recurrent high-grade tumor and radiation necrosis.

2. Coregistration of MR and FDG-PET images is essential for accurate evaluation and localization of brain tumors.

Differential Diagnosis List

See discussion.

ACR Codes and Keywords:

References and General Discussion of PET Tumor Imaging Studies (Anatomic field:Skull and Contents, Category:Neoplasm, Neoplastic-like condition)

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Case number: pt103

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