Prostate Cancer and Its Mimics-A Pictorial Review

Abstract

Background: Multiparametric prostate MRI (mpMRI) is gaining wider recommendations for diagnosing and following up on prostate cancer. However, despite the high accuracy of mpMRI, false positive and false negative results are reported. Some of these may be related to normal anatomic structures, benign lesions that may mimic cancer, or poor-quality images that hamper interpretation. The aim of this review is to discuss common potential pitfalls in the interpretation of mpMRI.

Methods: mpMRI of the prostates was performed on 3T MRI scanners (Philips Achieva or Siemens Magnetom Vida) according to European Society of Urogenital Radiology (ESUR) guidelines and technical requirements.

Results: This pictorial review discusses normal anatomical structures such as the anterior fibromuscular stroma, periprostatic venous plexus, central zone, and benign conditions such as benign prostate hyperplasia (BPH), post-biopsy hemorrhage, prostatitis, and abscess that may imitate prostate cancer, as well as the appearance of prostate cancer occurring in these locations. Furthermore, suggestions on how to avoid these pitfalls are provided, and the impact of image quality is also discussed.

Conclusions: In an era of accelerating prostate mpMRI and high demand for high-quality interpretation of the scans, radiologists should be aware of these potential pitfalls to improve their diagnostic accuracy.

Keywords: differential diagnosis; magnetic resonance imaging (MRI); mpMRI; pitfalls; prostate cancer.

Figure 1

Hypertrophied anterior fibromuscular stroma (normal anatomic structure—PI-RADS 1): axial (a) T2-w image presents hypertrophied AFMS with low signal intensity (arrows); with no diffusion restriction (b) DWI b 2000 image does not show increased signal intensity (arrows); (c) on ADC map it presents as low signal intensity due to T2-dark through effect (arrows); (d) and no enhancement on DCE (arrows); (e) whole mount histopathology after radical prostatectomy confirms the diagnosis depicting anterior fibromuscular stroma in the anterior part of the prostate (arrows).

Figure 1

Hypertrophied anterior fibromuscular stroma (normal anatomic structure—PI-RADS 1): axial (a) T2-w image presents hypertrophied AFMS with low signal intensity (arrows); with no diffusion restriction (b) DWI b 2000 image does not show increased signal intensity (arrows); (c) on ADC map it presents as low signal intensity due to T2-dark through effect (arrows); (d) and no enhancement on DCE (arrows); (e) whole mount histopathology after radical prostatectomy confirms the diagnosis depicting anterior fibromuscular stroma in the anterior part of the prostate (arrows).

Figure 2

Anterior prostate cancer invading AFMS (PI-RADS 5): axial (a) T2-w image presents a lenticular lesion in place of AFMS with low intensity signal of “erased charcoal” appearance (arrows); with diffusion restriction (b) high signal on DWI b 2000 image (arrows); (c) and low signal on ADC map (arrows); (d) early enhancement on DCE (arrows); (e) whole mount histopathology after radical prostatectomy reveals prostate cancer GS 4 + 3 in the anterior part of the prostate invading AFMS (outlined with a black continuous line).

Figure 2

Anterior prostate cancer invading AFMS (PI-RADS 5): axial (a) T2-w image presents a lenticular lesion in place of AFMS with low intensity signal of “erased charcoal” appearance (arrows); with diffusion restriction (b) high signal on DWI b 2000 image (arrows); (c) and low signal on ADC map (arrows); (d) early enhancement on DCE (arrows); (e) whole mount histopathology after radical prostatectomy reveals prostate cancer GS 4 + 3 in the anterior part of the prostate invading AFMS (outlined with a black continuous line).

Figure 3

Periprostatic venous plexus in the left postero-lateral side of the prostate, presenting on axial images as an oval structure with: (a) intermediate to low signal intensity on T2-w image on the left postero-lateral side of prostate, due to turbulent flow (arrow); moderate diffusion restriction; (b) increased signal on DWI b 2000 image (arrow); (c) decreased signal on ADC map (arrow); (d) but with no early focal enhancement (arrow).

Figure 3

Periprostatic venous plexus in the left postero-lateral side of the prostate, presenting on axial images as an oval structure with: (a) intermediate to low signal intensity on T2-w image on the left postero-lateral side of prostate, due to turbulent flow (arrow); moderate diffusion restriction; (b) increased signal on DWI b 2000 image (arrow); (c) decreased signal on ADC map (arrow); (d) but with no early focal enhancement (arrow).

Figure 4

(A) Normal central zone: (a) axial T2-w image shows homogenously hypointense, symmetric area at the base of the prostate (yellow arrows), surrounding ejaculatory ducts (white arrows); (b) coronal T2-w image shows homogenously hypointense, symmetric area in conical shape extending from the base of the prostate (yellow arrows) to verumontanum (white arrowhead); (c) with mildly increased signal on DWI b 2000 image (yellow arrows); (d) and mildly decrease on ADC map (yellow arrows); (e) and diffuse little enhancement of progressive type (yellow arrows). (B) Patient with enlarged TZ due to BPH. The central zone in this patient is compressed between enlarged TZ and normal PZ and displaced towards the base of the prostate—the so-called “moustache sign”: (a) axial and (b) coronal T2-w images show homogenously hypointense, symmetric area at the base of the prostate (arrows); (c) with mildly decreased signal on ADC map (arrows).

Figure 4

(A) Normal central zone: (a) axial T2-w image shows homogenously hypointense, symmetric area at the base of the prostate (yellow arrows), surrounding ejaculatory ducts (white arrows); (b) coronal T2-w image shows homogenously hypointense, symmetric area in conical shape extending from the base of the prostate (yellow arrows) to verumontanum (white arrowhead); (c) with mildly increased signal on DWI b 2000 image (yellow arrows); (d) and mildly decrease on ADC map (yellow arrows); (e) and diffuse little enhancement of progressive type (yellow arrows). (B) Patient with enlarged TZ due to BPH. The central zone in this patient is compressed between enlarged TZ and normal PZ and displaced towards the base of the prostate—the so-called “moustache sign”: (a) axial and (b) coronal T2-w images show homogenously hypointense, symmetric area at the base of the prostate (arrows); (c) with mildly decreased signal on ADC map (arrows).

Figure 5

Prostate cancer in central zone: T2-weighted images show the focal asymmetric area of low signal intensity adjacent to the left central zone in axial (a) and coronal (b) planes (arrow), with diffusion restriction on (c) DWI b 2000 image (arrow) and (d) ADC map (arrow), and early focal enhancement (f). The lesion was assessed as PI-RADS 4; (e) native T1-w fat-saturated images showing postbiopsy hemorrhage in the PZ (white arrows); (f) focal enhancement of the lesion adjacent to the left CZ (yellow arrow); (g) whole mount histopathology after radical prostatectomy revealing prostate cancer GS 4 + 3 in this area (outlined with continuous line). Additionally, on the images, the hypertrophied AFMS is visible in the anterior part of the prostate with low signal intensity on axial T2-w image (a), no diffusion restriction (c,d), and no enhancement (f), confirmed at whole mount histopathology after radical prostatectomy (red arrows) (g).

Figure 5

Prostate cancer in central zone: T2-weighted images show the focal asymmetric area of low signal intensity adjacent to the left central zone in axial (a) and coronal (b) planes (arrow), with diffusion restriction on (c) DWI b 2000 image (arrow) and (d) ADC map (arrow), and early focal enhancement (f). The lesion was assessed as PI-RADS 4; (e) native T1-w fat-saturated images showing postbiopsy hemorrhage in the PZ (white arrows); (f) focal enhancement of the lesion adjacent to the left CZ (yellow arrow); (g) whole mount histopathology after radical prostatectomy revealing prostate cancer GS 4 + 3 in this area (outlined with continuous line). Additionally, on the images, the hypertrophied AFMS is visible in the anterior part of the prostate with low signal intensity on axial T2-w image (a), no diffusion restriction (c,d), and no enhancement (f), confirmed at whole mount histopathology after radical prostatectomy (red arrows) (g).

Figure 6

Prostate cancer in the median posterior gland in a patient with PSA 21.36 ng/mL (a) axial and (b) coronal T2-weighted images showing a focal, ill-defined area of low signal intensity located in the median posterior area at the apex and middle third of the prostate (arrows), with marked diffusion restriction on (c) DWI b 2000 image (arrows) and (d) ADC map (arrows); and (e) early enhancement (arrows). The lesion was assessed as PI-RADS 5. (f) After radical prostatectomy, PCa GS 5 + 4 was diagnosed in this location (area outlined with black continuous line).

Figure 6

Prostate cancer in the median posterior gland in a patient with PSA 21.36 ng/mL (a) axial and (b) coronal T2-weighted images showing a focal, ill-defined area of low signal intensity located in the median posterior area at the apex and middle third of the prostate (arrows), with marked diffusion restriction on (c) DWI b 2000 image (arrows) and (d) ADC map (arrows); and (e) early enhancement (arrows). The lesion was assessed as PI-RADS 5. (f) After radical prostatectomy, PCa GS 5 + 4 was diagnosed in this location (area outlined with black continuous line).

Figure 7

Prostate cancer in the median posterior gland in a 48-year-old patient with PSA 9.75 ng/mL (a) axial and coronal (b) T2-weighted images show the focal, ill-defined area of low signal intensity (arrows), with marked diffusion restriction on (c) DWI b 2000 image (arrows) and (d) ADC map (arrows); and early enhancement (arrows) (e). The lesion was assessed as PI-RADS 4. (f) After radical prostatectomy, PCa GS 4 + 3 was diagnosed in this location (area outlined with black continuous line).

Figure 7

Prostate cancer in the median posterior gland in a 48-year-old patient with PSA 9.75 ng/mL (a) axial and coronal (b) T2-weighted images show the focal, ill-defined area of low signal intensity (arrows), with marked diffusion restriction on (c) DWI b 2000 image (arrows) and (d) ADC map (arrows); and early enhancement (arrows) (e). The lesion was assessed as PI-RADS 4. (f) After radical prostatectomy, PCa GS 4 + 3 was diagnosed in this location (area outlined with black continuous line).

Figure 8

(A) BPH nodules on T2W images: (a) typical, completely encapsulated BPH nodule (PI-RADS 1) (arrow); (b) hypointense, circumscribed stromal nodule within a larger encapsulated nodule (PI-RADS 1) (arrow); (c) typical, completely and partially encapsulated BPH nodules (PI-RADS 1 and PI-RADS 2) (arrows). (B) A 65-year-old patient with PSA 9.8 ng/mL: (a) T2W axial image and (b) whole mount histopathology specimen after prostatectomy show the acinar prostate adenocarcinoma in the PZ and TZ of the left lobe of the prostate (white arrow on T2W image (a) and outlined and marked area on histopathology specimen after prostatectomy (b)) and large completely encapsulated BPH nodule in the right lobe of prostate (yellow arrow on T2W image (a) and red arrow on histopathology specimen (b)).

Figure 9

Atypical BPH nodule in the transition zone: axial (a), sagittal (b), and coronal (c) T2-weighted images show homogenous, hypointense, partially encapsulated nodules (arrows), with marked diffusion restriction on (d) DWI b 2000 image (arrow) and (e) ADC map (arrow); and (f) enhancement on DCE (arrow). Overall PI-RADS score for this nodule: PI-RADS 3. (g) Histopathologically, it proved to be a stromal BPH nodule (arrow).

Figure 9

Atypical BPH nodule in the transition zone: axial (a), sagittal (b), and coronal (c) T2-weighted images show homogenous, hypointense, partially encapsulated nodules (arrows), with marked diffusion restriction on (d) DWI b 2000 image (arrow) and (e) ADC map (arrow); and (f) enhancement on DCE (arrow). Overall PI-RADS score for this nodule: PI-RADS 3. (g) Histopathologically, it proved to be a stromal BPH nodule (arrow).

Figure 10

Prostate cancer in the right lobe of prostate, mostly in the transition zone, invading anterior horn of PZ in 74-year-old patient with PSA level 6.84 ng/mL: (a) axial T2-w image shows a lenticular, hypointense lesion with “erased charcoal” appearance in the right TZ and anterior horn of PZ (arrow); with marked diffusion restriction (b) high signal on DWI b 2000 image (arrow); (c) and low signal on ADC map (arrow); (d) early enhancement on DCE (arrow); the lesion was assessed as PI-RADS 5; (e) whole-mount histopathology after radical prostatectomy revealed prostate cancer GS 3 + 4 in this area (area outlined with black continuous line).

Figure 10

Prostate cancer in the right lobe of prostate, mostly in the transition zone, invading anterior horn of PZ in 74-year-old patient with PSA level 6.84 ng/mL: (a) axial T2-w image shows a lenticular, hypointense lesion with “erased charcoal” appearance in the right TZ and anterior horn of PZ (arrow); with marked diffusion restriction (b) high signal on DWI b 2000 image (arrow); (c) and low signal on ADC map (arrow); (d) early enhancement on DCE (arrow); the lesion was assessed as PI-RADS 5; (e) whole-mount histopathology after radical prostatectomy revealed prostate cancer GS 3 + 4 in this area (area outlined with black continuous line).

Figure 11

Ectopic BPH nodule in the left peripheral zone: focal lesion with marked diffusion restriction with (a) high signal on DWI b 2000 image (arrow); (b) low signal on ADC map (arrow); (c) early and strong enhancement on DCE; (d) ROI for calculation of enhancement curve placed in the lesion on DCE; (e) enhancement curve in the lesion shows strong, early enhancement with washout—only in these sequences the lesion appear suspicious for malignancy. However, T2-weighted image (f) revealed completely encapsulated BPH nodule, which should be scored as benign—PI-RADS 1.

Figure 11

Ectopic BPH nodule in the left peripheral zone: focal lesion with marked diffusion restriction with (a) high signal on DWI b 2000 image (arrow); (b) low signal on ADC map (arrow); (c) early and strong enhancement on DCE; (d) ROI for calculation of enhancement curve placed in the lesion on DCE; (e) enhancement curve in the lesion shows strong, early enhancement with washout—only in these sequences the lesion appear suspicious for malignancy. However, T2-weighted image (f) revealed completely encapsulated BPH nodule, which should be scored as benign—PI-RADS 1.

Figure 12

Postbiopsy hemorrhage: (a) axial T2-w image shows the area of decreased signal in the right peripheral zone (arrow), with mild diffusion restriction (arrows) (b,c). However, the native T1-w fat-saturated image reveals the hyperintense signal in this location (arrow), which corresponds to methemoglobin (the product of hemoglobin degradation) after biopsy (d). After contrast administration, “pseudo enhancement” is noted (arrow) (e). The combination of images is in favor of PI-RADS 2 lesion. The final histopathology did not reveal cancer in this region.

Figure 13

T1 hemorrhage exclusion sign: (a) on T1-weighted image, almost the entire PZ demonstrates diffuse hyperintense signal due to hemorrhage, except for a hypointense focus in the left PZ, mid gland (arrow). This hypointense focal lesion in the otherwise hyperintense PZ in T1W images shows: (b) hypointense signal on T2W images (arrow) and marked diffusion restriction with (c) high signal on DWI b 2000 image (arrow); (d) and low signal on ADC map (arrow); (e,f) and early enhancement after contrast on DCE (arrows). The lesion was reported as PI-RADS 4. (g) PCa GS 5 + 4 was diagnosed after radical prostatectomy in the left PZ in this area (area outlined with black continuous line on whole mount histopathology specimen).

Figure 13

T1 hemorrhage exclusion sign: (a) on T1-weighted image, almost the entire PZ demonstrates diffuse hyperintense signal due to hemorrhage, except for a hypointense focus in the left PZ, mid gland (arrow). This hypointense focal lesion in the otherwise hyperintense PZ in T1W images shows: (b) hypointense signal on T2W images (arrow) and marked diffusion restriction with (c) high signal on DWI b 2000 image (arrow); (d) and low signal on ADC map (arrow); (e,f) and early enhancement after contrast on DCE (arrows). The lesion was reported as PI-RADS 4. (g) PCa GS 5 + 4 was diagnosed after radical prostatectomy in the left PZ in this area (area outlined with black continuous line on whole mount histopathology specimen).

Figure 14

Prostatitis in a 48-year-old patient with elevated PSA 5 ng/mL: (a) axial T2-w image shows diffuse, decreased signal in the peripheral zone (arrows), with moderate diffusion restriction; (b) diffuse, moderately increased signal on DWI b 2000 image (arrows); (c) diffuse, moderately decreased signal on ADC map (arrows); (d) mild, diffuse enhancement of PZ (arrows). Findings reported as PI-RADS 2.

Figure 15

Patient 82 years old, with PSA 7.49 ng/mL: (a) axial T2-w image shows diffuse, moderately decreased signal in the peripheral zone with two foci of lower signal intensity (arrows), which demonstrate focal, marked diffusion restriction (arrows) (b,c) and early enhancement on DCE (arrows) (d). The lesions were classified as PI-RADS 4 and biopsied. A histopathological examination did not reveal any cancer. Follow-up MRI at five months showed significant resolution of the lesions (arrow) (e) and, after one year, complete disappearance of the lesions (arrows) (f). PSA decreased to 0.3 ng/mL. Images demonstrate lesions in the course of prostatitis.

Figure 15

Patient 82 years old, with PSA 7.49 ng/mL: (a) axial T2-w image shows diffuse, moderately decreased signal in the peripheral zone with two foci of lower signal intensity (arrows), which demonstrate focal, marked diffusion restriction (arrows) (b,c) and early enhancement on DCE (arrows) (d). The lesions were classified as PI-RADS 4 and biopsied. A histopathological examination did not reveal any cancer. Follow-up MRI at five months showed significant resolution of the lesions (arrow) (e) and, after one year, complete disappearance of the lesions (arrows) (f). PSA decreased to 0.3 ng/mL. Images demonstrate lesions in the course of prostatitis.

Figure 16

Patient 76 years old, with PSA 10 ng/mL: (a,b) axial T2-w images show diffusely decreased signal in the entire prostate, with large, diffuse areas of lower “erased charcoal” signal intensity, which include both peripheral and transition zones in the apex and mid gland, more pronounced on the left, with bulging of the capsule in the apex on the left (arrows), marked diffusion restriction (arrows) (c–f), and strong, early enhancement on DCE (arrows) (g,h). The lesions were classified as PI-RADS 5 and biopsied. A histopathological examination revealed confluent foci of intensive active and chronic inflammation with glandular destruction and focal granuloma formation. No fungal infection or cancer was revealed. After treatment, PSA decreased to 4.6 ng/mL. The images listed above demonstrate diffuse, active granulomatous prostate inflammation.

Figure 16

Patient 76 years old, with PSA 10 ng/mL: (a,b) axial T2-w images show diffusely decreased signal in the entire prostate, with large, diffuse areas of lower “erased charcoal” signal intensity, which include both peripheral and transition zones in the apex and mid gland, more pronounced on the left, with bulging of the capsule in the apex on the left (arrows), marked diffusion restriction (arrows) (c–f), and strong, early enhancement on DCE (arrows) (g,h). The lesions were classified as PI-RADS 5 and biopsied. A histopathological examination revealed confluent foci of intensive active and chronic inflammation with glandular destruction and focal granuloma formation. No fungal infection or cancer was revealed. After treatment, PSA decreased to 4.6 ng/mL. The images listed above demonstrate diffuse, active granulomatous prostate inflammation.

Figure 17

Patient 61 years old, PSA 5 ng/mL. (a) Axial T2-w image shows a diffuse low intensity signal of “erased charcoal” appearance in almost entire prostate gland, involving peripheral and transition zones (arrows); with marked diffusion restriction (b) high signal on DWI b 2000 image in almost entire prostate (arrows); (c) corresponding to low signal on ADC map (arrows); (d) and early enhancement on DCE (arrows); The lesion was assessed as PI-RADS 5. (e) diffuse prostate cancer GS 5 + 4 was revealed in this area on whole mount histopathology specimen after radical prostatectomy (area outlined with black continuous line).

Figure 18

Abscess in the transition zone of the prostate: (a) axial T2-w image shows hyperintense, oval lesion in the left transition zone at the base of the prostate, with hypointense rim (arrow); (b) axial T1-w image shows isointense oval lesion, with slightly hyperintense rim (arrow); (c) with marked diffusion restriction high signal on DWI b 2000 (arrow); (d) corresponding to very low signal on ADC map (arrows); (e) rim enhancement on DCE (arrow); lesion was reported as PI-RADS 2; (f) after antibiotic treatment, the abscess persisted, but in T2-w images, its signal changed to intermediate intensity (arrow).

Figure 19

DWI sequence affected by artifacts from the gas in the rectum—rendering interpretation of the PZ in posterior gland impossible: (a) DWI b 2000; (b) ADC map. However, in this patient, a focal early enhancement is visible on DCE (arrow) (c), which corresponds to a poorly visible, hypointense focal lesion on T2-weigted image (arrow) (d), on the background of a larger area of reduced signal intensity; the lesion was reported as PI-RADS 4; (e) whole-mount histopathology after radical prostatectomy reveals prostate cancer GS 4 + 3 in this location in the right PZ (area outlined with black continuous line).

Figure 19

DWI sequence affected by artifacts from the gas in the rectum—rendering interpretation of the PZ in posterior gland impossible: (a) DWI b 2000; (b) ADC map. However, in this patient, a focal early enhancement is visible on DCE (arrow) (c), which corresponds to a poorly visible, hypointense focal lesion on T2-weigted image (arrow) (d), on the background of a larger area of reduced signal intensity; the lesion was reported as PI-RADS 4; (e) whole-mount histopathology after radical prostatectomy reveals prostate cancer GS 4 + 3 in this location in the right PZ (area outlined with black continuous line).