To present the imaging characteristics of mpMRI and PET/CT, as well as their correlation with histopathological findings, in the diagnosis, staging, treatment response monitoring, and detection of recurrence, in a rare case of primary prostatic lymphoma.
A 59-year-old male patient with complaints of fever, chills and night sweats was referred to urology after dysuria and hematuria emerged. Multiparametric prostate MRI examination was performed when the serum PSA value was 5.26 ng/ml with a PSA density of 0.26 ng/ml2. mpMRI revealed non-circumscribed moderate hypointense areas on axial T2-weighted images (T2WI) in the bilateral peripheral zone, with restricted diffusion on diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) map images, as well as diffuse enhancement on dynamic contrast-enhanced (DCE) images (Image 1, 2). The mpMRI findings, together with the clinical presentation, primarily suggested prostatitis, and a treatment including antibiotherapy initiated. However, as there was no clinical response to the treatment, it was decided to perform a transrectal ultrasound guided prostate biopsy. Histopathological examination of the prostate biopsy revealed Diffuse Large B-cell Lymphoma (Image 3). 18F-FDG PET/CT revealed no extraprostatic involvement in the body. In the prostate gland, an increased FDG-uptake was observed with a SUVmax value of 5.40 (Image 4). Therefore, the diagnosis of the patient was considered as primary prostatic lymphoma. The patient underwent chemotherapy and subsequent radiotherapy for prostatic lymphoma. The hypermetabolic lesion in the prostate gland completely disappeared on a follow-up PET/CT scan after therapy, indicating a treatment response (Image 5). However in the second year, when the serum PSA value was 0.33 ng/ml, a newly emerged focal hypermetabolic focus with a SUVmax value of 4.93 was observed in the right lobe of the prostate gland on PET/CT images (Image 6). Recurrent active lymphoma infiltration was considered. Multiparametric MRI of the prostate was performed to detect the recurrence of lymphoma. In the mpMRI, no findings consistent with active lymphoma infiltration were detected (Image 7). Nevertheless, a cognitive targeted biopsy was performed based on the PET/CT findings. Histopathologic examination revealed benign prostatic tissues and prostatitis findings, and no neoplastic lymphoid cell infiltration (Image 8).
In the bilateral peripheral zone, non-circumscribed moderate hypointense areas on axial T2-weighted image (T2WI) is seen. T2 hypointense areas in the peripheral zone show restricted diffusion with high signal on diffusion-weighted imaging (DWI) and low signal on the apparent diffusion coefficient (ADC) map (ADC value; 700 µm²/sec).
Dynamic contrast-enhanced (DCE) MRI image shows increased signal intensity with a type 1 curve in the peripheral zone.
A- Numerous large neoplastic lymphoid cell infiltrations between the stroma of prostate glands with a natural appearance (H&E). B- In the p63-AMACR dual immunohistochemical examination, p63 has stained the basal cell layer of the prostate glands with a natural appearance in brown color, and AMACR (-) has been detected in secretory cells. C- Diffuse CD20 expression in neoplastic lymphoid cells. D- Diffuse BCL-2 expression in neoplastic lymphoid cells. E- Neoplastic lymphoid cells have tested negative for CD10. F- Neoplastic lymphoid cells have tested negative for BCL-6. G- Less than 30% expression of MUM-1 in neoplastic lymphoid cells. H- Less than 40% expression of C-MYC in neoplastic lymphoid cells.
More than 90% of prostate malignant neoplasms are adenocarcinomas, and other subtypes are extremely rare. Primary prostatic lymphomas <1% of these neoplasms. The most common histological type of prostatic non-Hodgkin lymphoma is Diffuse Large B-cell Lymphoma [Taleb et al], as in our case. Primary prostatic lymphoma is observed in elderly male populations, with an average age of diagnosis at 62 [Wang et al] PSA levels show an increase in approximately 20% of cases and often rise to levels around 4 ng/mL [Hu et al]. In our case, PSA level at diagnosis was 5.26 ng/mL, which decreased to 0.33 ng/mL after the treatment. Treatment approaches for primary prostatic lymphoma include radiation therapy, chemotherapy, and chemoradiotherapy, similar to other lymphoma types [Wang et al]. Due to the rarity of the disease, prognosis evaluation is not well-defined. In a retrospective study by Bostwick involving 62 patients, the 5-year survival rate was only 33%, and the rate of developing metastasis within 59 months was 73% [Bostwick et al] FDG-PET/CT stands as the main imaging modality in lymphoma [Al Tabaa et al]. In modern approaches to managing Hodgkin lymphoma and aggressive non-Hodgkin lymphoma, 18F-FDG PET/CT has become essential for staging processes. It holds a significant position in staging, restaging, predicting outcomes, devising suitable treatment approaches, overseeing therapy progress, and identifying instances of recurrence [D'souza et al]. The diagnostic and staging utility of FDG-PET/CT might have limitations when dealing with diseases confined within organs, potentially leading to false negatives due to the overlap of tumor uptake with normal tissue, BPH, and scar tissue. Conversely, false positives can occur in the presence of inflammatory conditions [Jadvar et al]. In mpMRI, prostate lymphoma exhibits imaging characteristics similar to prostatitis, as in our case. Typically, prostatic lymphoma exhibit a uniform isointense signal on T1WI/T2WI, and they manifest as uniformly restricted diffusion on DWI and ADC maps. Moderate enhancement of the lesion can potentially be visualized on DCE imaging [Han et al].
18F-FDG PET/CT revealed no extraprostatic involvement in the body. In the prostate gland, an increased FDG-uptake was observed with a SUVmax value of 5.40.
The patient underwent chemotherapy and subsequent radiotherapy for prostatic lymphoma. The hypermetabolic lesion in the prostate gland completely disappeared on a follow-up PET/CT scan after therapy, indicating a treatment response.
However in the second year, when the serum PSA value was 0.33 ng/ml, a newly emerged focal hypermetabolic focus with a SUVmax value of 4.93 was observed in the right lobe of the prostate gland on PET/CT images.
To our knowledge, this is the best documented case of primary lymphoma of the prostate, encompassing pre-treatment and follow-up imaging findings along with histopathological correlation. Although primary prostate lymphoma is exceedingly uncommon, lymphoma should always be considered in the differential diagnosis in cases with a prostatitis-like appearance on mpMRI. In our case, 18F-FDG PET/CT showed a false positive result, likely due to prostatitis, in the posttreatment follow-up for recurrence. On the other hand, mpMRI findings seem to be more compatible with histopathological results at diagnosis and monitoring of local recurrence.
Multiparametric MRI of the prostate was performed to detect the recurrence of lymphoma. Axial T2W image shows diffuse hypointensity in the prostate due to the treatment. High b value DWI and ADC map images show no lesion with diffusion restriction. DCE image shows no enhancing lesion.
In sections of the biopsy materials taken 2 years after the treatment, benign prostatic tissues and prostatitis findings have been observed, and no neoplastic lymphoid cell infiltration has been detected (H&E).
