Prostatitis: imaging appearances and diagnostic considerations

[madman]

Acute and chronic inflammation of the prostate gland can be attributed to several underlying aetiologies, including but not limited to, bacterial prostatitis, granulomatous prostatitis, and Immunoglobulin G4-related prostatitis. In this review, we provide an overview of the general imaging appearances of the different types of prostatitis, their distinguishing features, and characteristic appearances at cross-sectional imaging. Common imaging pitfalls are presented and illustrated with examples.




Introduction

Prostatitis is an inflammatory condition of the prostate with a prevalence of 8.7%,1 which encompasses several conditions including acute and chronic bacterial prostatitis, granulomatous prostatitis, and Immunoglobulin G4 (IgG4)-related prostatitis.2,3 Although recent advances in multiparametric prostate magnetic resonance imaging (MRI) have improved significantly, the diagnostic accuracy of prostatitis and its mimics is limited by the many overlapping radiological features, which can make the differentiation from clinically significant prostate carcinoma challenging. The purpose of this review is to illustrate the multimodality imaging appearances of the various subtypes of prostatitis and when to consider this diagnosis. We also aim to emphasize the key imaging features that can help make a distinction of prostatitis from other conditions, namely prostate carcinoma.




Bacterial prostatitis
*Imaging features
*Management

Granulomatous prostatitis
*Imaging features

IgG4-related prostatitis
*Imaging features




Conclusion

Prostatitis encompasses several entities, which have overlapping clinical and radiological features. Accurate diagnosis of the specific type of prostatitis is important so the correct therapy can be initiated, and unnecessary surgical intervention avoided. The main MRI findings include focal or diffuse prostate enlargement, T2 signal hypointensity, diffusion restriction, and corresponding low signal intensity on ADC maps. A previous history of BCG immunotherapy confirmed TB infection, or TURP should prompt consideration of a diagnosis of granulomatous prostatitis. In patients with metachronous organ involvement outside of the prostate gland, IgG4-related disease should be considered. The synchronous disease should also be sought, as IgG4-related disease responds well to corticosteroid therapy and immunomodulators.

The radiological features of prostatitis often overlap with prostate carcinoma, which is the most important differential diagnosis to consider. On T2WI, the hypointense T2 signal areas in prostatitis are usually geographic and ill-defined and generally do not exert mass effect on the adjacent normal prostate tissue in contrast with prostate carcinoma. Although both diseases demonstrate diffusion restriction, in prostatitis it is usually to a lesser degree than seen in prostate carcinoma.52,53 Similarly the ADC values tend to be higher in prostatitis patients compared with prostate carcinoma patients11, 12. Although prostatitis can mimic prostate carcinoma radiologically, it is important to bear in mind the two may coexist.54

 

[madman]

Figure 1 (a) Axial and (b) coronal mpMRI images of a 65-year-old man demonstrated a well-demarcated T2 hypointense lesion in the left peripheral zone (arrow) with the corresponding signal loss on the ADC maps (c, arrow). The band-like shaped morphology and absence of a mass effect are most consistent with bacterial prostatitis.

 

[madman]

Figure 2 (a) Axial and (b) coronal mpMRI images of a 57-year-old man demonstrated a T2 hypointense lesion (white arrows) in the left peripheral zone with corresponding restricted diffusion (c, arrow) and signal loss on the ADC maps (d, arrow). The wedge-shaped morphology, together with the lack of contour deformity of the adjacent prostate tissue and the capsule is most consistent with bacterial prostatitis.

 

[madman]

Figure 3 A 65-year-old man with a history of metastatic colorectal adenocarcinoma. MRI pelvis as part of surveillance imaging demonstrated prostatomegaly with a new 1.5 cm T2 hypointense focus in the left posterolateral peripheral zone (a, arrow) with abnormal enhancement (b, arrow), restricted diffusion (c, arrow), and signal loss on ADC maps (d, arrow). This patient was treated for prostatitis and follow-up imaging confirmed interval resolution of signal abnormalities in the prostate gland.

 

[madman]

Figure 4 A 60-year-old man with acute bacterial prostatitis and sepsis. Follow-up mpMRI 2 months after treatment with antibiotics, demonstrated asymmetric enlargement of the right prostate gland with interval development of a 2 cm T2 hyperintense (a, arrows) rim-enhancing (b, arrows) fluid collection in the right mid-peripheral zone with restricted diffusion (c, arrows) and loss of signal on the ADC maps (d, arrows). These findings are likely in keeping with post-infectious/inflammatory focal fluid collections.

 

[madman]

Figure 5 A 59-year-old man with fever, urinary tract infection, and pyuria. (a) The contrast-enhanced CT demonstrated a heterogeneous prostate gland (arrow). (b) The follow-up mpMRI demonstrated a 3.2 cm T2 hypointense lesion (arrows) involving the majority of the right prostate lobe, which demonstrated abnormal enhancement (arrow, (c) and restricted diffusion (d, arrows) with a corresponding signal loss on ADC (e, arrows). Prostate biopsy revealed benign prostate tissue with dense granulomatous and lymphoplasmacytic inflammation with scattered microabscesses in the right gland in keeping with non-specific granulomatous prostatitis.

 

[madman]

Figure 6 (a) A 65-year-old man with a history of bladder transitional cell carcinoma and BCG treatment underwent mpMRI, which demonstrated background T2 hypointensity involving the majority of the bilateral peripheral zones. There are superimposed nodules in the mid and right posterior peripheral zone that demonstrate more pronounced T2 hypointensity (a, arrows), smooth rim enhancement (b, arrows), and restricted diffusion (c, arrows) with a signal loss on the ADC maps (d, arrows). Prostate biopsy demonstrated prostatic tissue with atrophic changes and chronic inflammation with granulomatous inflammation in keeping with BCG granulomatous prostatitis. The smooth rim enhancement of nodules represents the pseudo-capsule with granulation tissue.

 

[madman]

Figure 7 A 71-year-old man with a history of bladder transitional cell carcinoma receiving BCG therapy presented for mpMRI that demonstrated a 2 cm T2 hypointense lesion (a, arrows) in the right peripheral zone with abnormal enhancement (b, black arrow) with a focal area of hypoenhancement medially (b, white arrow), restricted diffusion with increased signal intensity medially (c, arrow) and corresponding signal loss on the ADC maps (d, arrow) representing focal necrosis. Prostate biopsy demonstrated necrotizing granulomas in keeping with BCG treatment effect.

 

[madman]

Figure 8 A 32-year-old man with flu-like myalgias and headache in the setting of VGKC autoantibodies. PET-CT was performed to assess for paraneoplastic syndrome and demonstrated asymmetric intense FDG uptake in the left prostate gland (a, arrow). mpMRI, 9 months later, demonstrated diffuse abnormal T2 hypointensity (b, arrows) involving nearly the entirety of the bilateral peripheral zones with associated abnormal enhancement (c, arrows), restricted diffusion (d, arrows), and signal loss on ADC maps (e, arrows). These findings were most compatible with IgG4 related prostatitis (prostate-specific antigen 0.8 ng/ml).

 

[madman]

Figure 9 A 78-year-old man with IgG4 disease. PET-CT demonstrated peri-aortic enhancing soft tissue (a,b, arrows) with corresponding increased FDG activity (c,d, arrows) in keeping with IgG4-related aortic vascular disease. The same PET-CT also demonstrated increased FDG activity within the prostate gland, in keeping with IgG4 prostatitis (e, arrow).