Fluciclovine F-18 PET-CT imaging findings of sacral and sciatic nerve perineural invasion in prostate cancer

1194 Objectives: Review of recently proposed mechanisms and pathophysiology of perineural invasion from prostatic malignancy.-Describe MRI and PET-CT imaging findings of perineural invasion in prostate cancer.-Present an unreported case to this date of Fluciclovine F-18 PET-CT imaging findings of tumoral perineural invasion as recurrence of treated prostate adenocarcinoma (biopsy-proven).-Discuss possible advantages of using prostate-specific PET radio-tracers in cases with suspicion of perineural invasion from prostate cancer. Methods: Perineural invasion, defined as the growth of cancer cells into any of the nerve sheath layers in the tumor microenvironment, has been reported in up to 43% of prostate biopsies with evidence of adenocarcinoma and nearly present in all of the specimens with positive extracapsular spread. Although histologically and clinically is a recognized phenomenon, its pathophysiology understanding remains limited and prevalence underappreciated. Overtime it is an entity that is still considered rare but it is being increasingly recognized due to abnormal radiographic findings with biopsy-proven correlate.Recently proposed mechanisms for perineural invasion include the role of Schwann cells in promotion of cancer cells migration and invasion as well as the blood nerve barrier as a microenvironment providing the tumor immunological and chemical protection. It is thought that malignant cells in prostate cancer invade the inferior hypogastric plexus surrounding the prostate and spread through the pelvic and sacral splanchnic nerves reaching the lumbosacral plexus. A process presumed to progress slowly with emerging symptoms even years after prostatectomy. In this review, we discuss the scientific literature regarding perineural invasion mechanisms in prostate cancer. We also present a biopsy-proven case of perineural invasion demonstrated on prostate-specific radiotracer Fluciclovine F-18 PET-CT imaging, which to our knowledge is the first to be reported to this date. Results: MRI with contrast may demonstrate radiographic abnormalities of perineural spread such as nerve enlargement, nodular pattern of nerve enhancement, muscle atrophy due to denervation and in some cases thickening of the ipsilateral rectal fascia. However differentiation of neoplastic plexopathy between other etiologies for example radiation or chemotherapy induced neuritis and primary malignancies is challenging. Combining imaging modalities, MRI with PET-CT can be very useful in elucidating a neoplastic etiology. Although there is no conclusive evidence, it has been recommended to favor prostate-specific PET radio-tracers over FDG-PET given the intrinsic decreased glucose uptake seen in prostate adenocarcinoma compared to other malignant tumors. There are still no standardized values for abnormal peripheral nerve radiotracer uptake and studies with comparison between radiotracers are still yet to be done. Ultimately biopsy remains the gold standard for tumor invasion confirmation. Conclusions: Tumoral perineural invasion in prostatic cancer is an under recognized and incompletely elucidated phenomenon that is increasingly being reported due to positive radiographic findings.-Combining MRI and PET-CT imaging modalities has been suggested to improve radiographic accuracy during evaluation of lumbosacral plexopathies in patients with prostatic adenocarcinoma.-Imaging with prostate-specific PET radio-tracers in cases with suspicion of lumbosacral plexopathy and history of prostate cancer, may prove useful to narrow the differential diagnosis by potentially excluding inflammatory or non-prostatic malignancy etiologies.