Case Author(s): Jeff Chesnut, D.O. and Farrokh Dedashti, M.D. , 5/22/99 . Rating: #D2, #Q3

Diagnosis: Adenoid cystic carcinoma metastatic to the left temporal lobe.

Brief history:

72 year old female with history of adenoid cystic carcinoma of the cavernous sinus resected and treated with radiation therapy with multiple recurrances.


Coronal slices of the brain are shown.

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View second image(pt). An isolated coronal view of the brain is shown

View third image(pt). Three contiguous transaxial slices through the temporal lobes are shown.

View fourth image(mr). A single slice from a T1 weighted gadolinium enhanced MRI is shown.

Full history/Diagnosis is available below

Diagnosis: Adenoid cystic carcinoma metastatic to the left temporal lobe.

Full history:

72 year old woman with a history of adenoid cystic carcinoma of the cavernous sinus resected and treated with radiation therapy in 1989. She had a recurrance in 1993 for which she underwent a left maxillary sinus dissection and left orbital evisceration. In 1995, she had another recurrence which was treated with sterotactic surgery and another small course of radiation therapy. MRI now demonstrates a new enhancing lesion of the anteromedial left temporal lobe and thickening of the left fifth nerve in its cranial portion. The patient describes new pain and numbness in the left face and head. The clinical question is recurrent malignancy vs. radiation necrosis.


F-18 flouro-deoxyglucose (FDG)


There is an intense focus of activity (with greater activity that the adjacent cortex) correlating with the small enhancing lesion of the anteromedial temporal lobe that is seen on MRI. This is consistent recurrent tumor. In addition, there is moderately increased activity in the region of the surgical bed in the inferior nasa cavity/sphenoid sinus and in the region of Meckel's cave (along the course of the fifth cranial nerve.) This also is suspicious for tumor recurrence in the surgical bed.


FDG-PET is very sensitive for the differentiation recurrent tumor from radiation necrosis in most cranial and extracranial malignancies. In an area of previous radiation therapy, presence of activity is suspicious for tumor recurrence. False negative findings can occur in low-grade neoplasms and false-positive findings may occur in infection such as abscess (though this should be easily differentiated by the clinical exam.

Sometimes, color scales may be helpful in examining a PET study of the brain. Care must be taken, however, not to overinterpret subtle changes that are accentuated by color. Most gray scales used in medical imaging possess 264 shades of gray. Color scales, on the other hand, invariably consist of many less gradations. Because of this, smaller differences in the intensity of a lesion may produces dramatic differences in color. If color is used in interpretation of PET studies, therefore, it is wise to use color to draw attention to an area, then evaluate that area in gray scale.

References: 1. Radiology 1993; 189:807-12. 2. Cancer 1994; 73:3074-58.


Patient received radiation and underwent tumor resection following radiotherapy.

View followup image(pt). A single transaxial view of the brain in rainbow color scale is shown.

Major teaching point(s):

FDG-PET is a reliable in differentiating recurrent/residual tumor from radiation necrosis.

Differential Diagnosis List

Recurrent tumor vs. inflammation

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: pt022

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