PSMA PET/CT scan reveals incidental meningioma in a prostate cancer patient

Abstract

As PSMA-PET/CT is routinely used for prostate cancer diagnosis due to its improved accuracy over traditional imaging techniques, an increasing number of non-prostate lesions are also being identified. Here, we report a patient with prostate adenocarcinoma, who was diagnosed with a synchronous atypical meningioma during PSMA PET/CT staging. Although PSMA PET/CT is a valuable tool in prostate cancer management, its limitations must be considered when assessing non-prostate lesions to minimize the risk of diagnostic errors.

1 Introduction

Prostate Specific Membrane Antigen (PSMA) -directed positron emission tomography/computed tomography (PET/CT) has been proven to detect prostate cancer lesions with high sensitivity and specificity compared to conventional imaging techniques. As a result, it has gained significant importance in staging prostate cancer patients, particularly those with biochemical recurrence or those requiring evaluation of lymph node involvement or metastatic lesions. Despite the increased accuracy of PSMA-PET/CT, it is known that non-prostatic lesions can also exhibit increased avidity, occasionally leading to the diagnosis of previously unknown pathologies outside prostate. However, this non-specific uptake can sometimes complicate the differential diagnosis between benign and malignant conditions. Here, we report the incidental discovery of an atypical meningioma in a prostate cancer patient who was suspected of having disseminated disease.

2 Case presentation

A 46-year-old male patient with a past medical history of hypercholesteremia and hypertension on lisinopril, was diagnosed with pT2cN0M0R1 prostate adenocarcinoma in 2023. His initial PSA was 20.7 ng/ml and a post-biopsy 18F -DCFPyL PSMA PET/CT scan revealed a 1.5 × 1.8 cm prostatic focus of intense tracer activity, consistent with a primary prostate adenocarcinoma. In addition, a focus of mildly increased tracer activity in the right frontotemporal lobe was identified as atypical for metastatic prostate cancer and categorized as a PSMA-RADS-3D lesion. Further imaging with brain MRI confirmed the presence of an enhancing extra-axial dural mass measuring 2.9 × 3.3 cm, compatible with meningioma ( Fig. 1 ). The patient then underwent a robotic-assisted radical prostatectomy. The pathology was significant for Gleason 3 + 4 = 7 disease with positive margins. Nine months after prostate removal, PSA levels rose to 0.067 ng/ml and were managed with PSA surveillance for 3 months.

A follow-up brain MRI one year after the detection of the right frontotemporal mass demonstrated slightly increased dimensions, now measuring 2.9 × 3.6 cm. Due to the increasing growth of the brain mass, surgical removal was scheduled. At the same time, repeat PSA testing showed an increase to 0.13 ng/ml and the Decipher score indicated an intermediate risk for metastatic disease. Given the PSA rise, a pelvic MRI and PSMA PET/CT for staging were requested before the brain surgery. Pelvic MRI revealed enhancing lesions in the left iliac and right pubic bones. However, the subsequent PSMA PET/CT showed no discrete uptake in these lesions but detected some new focal areas of mild PSMA uptake in the sacrum and in bilateral ribs, while confirming an unchanged mild uptake in the right parietotemporal region (SUV max: 1.5) ( Fig. 1 ). Imaging was reviewed by the tumor board, concluding that the bony lesions were unlikely due to metastatic disease and that the biochemical recurrence was likely due to a prostate bed recurrence.

The patient underwent his scheduled right supine craniotomy, without intraoperative complications, after which he initiated androgen deprivation therapy (ADT) treatment for his prostate cancer. The pathology from the brain surgery returned consistent with atypical meningioma, WHO grade 2. Additional PSMA and ERG staining was negative in tumor cells and highlighted only the blood vessels, as expected ( Fig. 2 ). The patient was referred to radiation oncology to discuss postoperative radiotherapy. Due to the complete resection of the brain tumor and the need to treat prostate cancer, patient will be monitored for recurrence. The patient is planned for prostate bed and pelvic nodal irradiation with 6 months of ADT.