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PERINEURAL SPREAD OF PAROTID SQUAMOUS CELL CARCINOMA ON 18F-FDG PET/CT
Authored By: Keith Fischer and Chad Wright.
Patient: 66 year old male
History: 66-year-old man with right parotid gland squamous cell carcinoma status post radiation who presents with double vision. Recent MRI suggested perineural spread of tumor along the right V3 nerve.
Image Size:[small][as-submitted]

Fig. 1
Contrast-enhanced MRI - T2 weighted axial image (left) and multiple serial post-contrast T1 weighted axial images (right)

Fig. 2
18F-FDG PET/CT - Axial CT (left), PET (middle), and fused PET/CT (right) images at the level of the skull base.

Fig. 3
18F-FDG PET/CT - Axial, sagittal and coronal fused PET/CT images demonstrating abnormally increased FDG uptake along the course of the right V3 nerve.

Fig. 4
18F-FDG PET fused with prior constrast-enhanced MRI - Axial PET (top), axial post-contrast T1 weighted MRI (middle), and fused PET/MRI (bottom) images at the level of the skull base.
Image Size:[small][as-submitted]

Findings:

Contrast-enhanced MRI:

 

Postsurgical changes consistent with a right parotidectomy are noted without evidence of enhancing tissue within the resection bed.  There is enhancement along the entire course of the right V3 nerve extending from the right pons, right trigeminal ganglion, right Meckel's cave, extending through the right foramen ovale, and into the right muscles of mastication. 

 

18F-FDG PET/CT:

 

There is increased radiotracer uptake in the medial aspect of the right temporal lobe in the region of Meckel's cave and foramen ovale which extends to the anterior and right-sided pons.  There is also prominence of the right foramen ovale when compared with the left.  Incidentally, there is diffuse moderately increased radiotracer uptake in the thyroid gland, which can be seen in Hashimoto's thyroiditis. 

 

The PET images were also fused with the patient's prior contrast-enhanced MRI for further anatomic correlation and assessment.

Diagnosis: Perineural spread of recurrent right parotid squamous cell carcinoma along the right V3 nerve.
General Discussion: This particular case highlights perineural spread which was very FDG-avid and demonstrates expansion of the foramen ovale.  However, perineural spread may be underestimated on FDG-PET due to small tumor volume as well as partial volume averaging with adjacent normal tissues.  As a consequence, semiquantitative assessment of FDG uptake associated with perineural spread may fall within the benign FDG uptake range.  Therefore careful visual examination of the skull base is necessary in such cases in order to detect subtle FDG uptake associated with malignant perineural spread. 
References: Fukui MB, Blodgett TM, Snyderman CH, Johnson JJ, Myers EN, Townsend DW and Meltzer CC.  Combined PET-CT in the Head and Neck.  Part 2.  Diagnostic Uses and Pitfalls of Oncologic Imaging.  Radiographics.  2005.  Volume 25.  Pages 913-930.
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Additional Details:

Case Number: 387927Owner(s): Keith Fischer and Chad WrightLast Updated: 02-07-2013
Anatomy: Cranium and Contents   Pathology: Neoplasm
Modality: CT, MR, PETAccess Level: Readable and writable by Nuclear Medicine only

Case has been viewed 12 times.
Certified by Keith Fischer on 01-23-2013

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