[¹⁸F]PSMA-1007 PET/CT in the detection of neoplastic lumbosacral plexopathy as an emerging and underestimated spread of prostate cancer

Excerpt

An 83-year-old patient  with a prostate adenocarcinoma in the left lobe (cT2N0M0, Gleason 8, iPSA 7.6 ng/ml) was initially treated with radiotherapy and hormone therapy. He underwent an [ ¹⁸F]PSMA-1007 PET/CT in the context of biochemical recurrence (PSA 4.5 ng/ml) and continuous low back pain, with a negative abdominal CT and bone scintigraphy. PET/CT revealed an intense sacral intradural [ ¹⁸F]PSMA-1007 uptake (Fig. 1A, C, G; red arrow), extending through the sacral foramina distally towards the S2/S3 nerves (Fig. 1B, D, G; green arrow), the sciatic nerve (Fig. 1B, D, G; yellow arrow), and the autonomic nerves innervating the prostate (Fig. 1B, D, G; blue arrow), as well as proximally towards the hypogastric plexus (Fig. 1A, C, G; black arrow). Perineural involvement (PNI) of prostate cancer is thought to be the earliest route of extraprostatic spread via the rich autonomic innervation of the prostate posterior aspect, and is an emerging cause of neoplastic lumbosacral plexopathy (nLSP) as an underestimated source of patient morbidity and mortality [ 1‐ 3]. The most common initial symptom of nLSP is pain followed by weakness and sensory disturbances, often misdiagnosed as radiculopathy or radiation-induced nerve injury. PNI is difficult to recognize on MRI, especially after pelvic radiation, as was the case in our patient, with hard-to-delineate abnormalities on the T1-weighted TSE MRI 5 days later (Fig. 1E. F; white circles) [ 3, 4]. To our knowledge, this is the first case in which nLSP is extensively visible on [ ¹⁸F]PSMA-1007 PET/CT, stressing the importance of the knowledge of the neuroanatomy to detect this common though often more subtle spread of prostate cancer.

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