Multi-parametric MRI of the Prostate

One in six men will develop prostate cancer in their lifetime [1]. The most consistent risk factors for the development of prostate cancer are advancing age, family history and race [2]. Interestingly, men in South East Asian countries have a lower incidence of prostate cancer that increases rapidly after immigration to the West suggesting that the pathogenesis of prostate cancer reflects both hereditary and environmental components [2]. It has been suggested that chronic inflammation might be important in prostate carcinogenesis. Intraprostatic inflammation might be caused by infections such as sexually transmitted agents; cell injury from exposure to chemical or physical trauma from urine reflux and prostatic calculi formation; hormonal variations or exposures and dietary factors such as charred meats. This may directly injure the prostate epithelium, resulting in histological lesions known as proliferative inflammatory atrophy (PIA). Transitions between areas of PIA and high grade prostatic intraepithelial neoplasia and adenocarcinoma have been observed [2]. Furthermore, PIA lesions may be a manifestation of the 'field effect' caused by environmental exposures [2]. In fact, prostate cancer is histologically heterogeneous and multifocal in as many as 85% of patients [3].


Introduction
One in six men will develop prostate cancer in their lifetime [1].The most consistent risk factors for the development of prostate cancer are advancing age, family history and race [2].Interestingly, men in South East Asian countries have a lower incidence of prostate cancer that increases rapidly after immigration to the West suggesting that the pathogenesis of prostate cancer reflects both hereditary and environmental components [2].It has been suggested that chronic inflammation might be important in prostate carcinogenesis.
Intraprostatic inflammation might be caused by infections such as sexually transmitted agents; cell injury from exposure to chemical or physical trauma from urine reflux and prostatic calculi formation; hormonal variations or exposures and dietary factors such as charred meats.This may directly injure the prostate epithelium, resulting in histological lesions known as proliferative inflammatory atrophy (PIA).
Transitions between areas of PIA and high grade prostatic intraepithelial neoplasia and adenocarcinoma have been observed [2].Furthermore, PIA lesions may be a manifestation of the 'field effect' caused by environmental exposures [2].In fact, prostate cancer is histologically heterogeneous and multifocal in as many as 85% of patients

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The Sri Lanka Journal of Surgery 2014; 32(1): 3-9 Figure 1.76-yr-old man with raised PSA.TRUS biopsy confirmed prostatic acinar adenocarcinoma, Gleason grade 3+4=7.(a) Axial T2WI shows lenticular shaped area with 'erased charcoal sign' in the right anterior central gland invading the FMZ likely representing cancer.A second hypointense lesion is seen in the left PZ with irregularity of the prostate capsule and thickening of the left neurovascular bundle (arrow) in keeping with tumour infiltration.(b) ADC map shows both lesions have restricted diffusion.(c) DCE-MRI with two ROis placed on the central gland lesion.(d) Graph of relative enhancement versus time.The dynamic enhancement curves show rapid contrast enhancement with high peak relative enhancement and contrast washout in keeping with carcinoma.Note that ROi1 has been placed on part of the lesion with lower ADC value and has a higher peak relative enhancement and washout in keeping with a more aggressive focus of cancer.(e) Axial T2WI more inferiorly in the prostate again shows the lesion in the central gland with irregular margins.The second lesion in the left PZ is seen as a rounded mass with bulging of the capsule consistent with capsular infiltration.(f) ADC map shows both lesions have restricted diffusion involving a large volume of the prostate.(g) DCE-MRI with ROi1 placed on the lesion in the left PZ and ROi2 placed on contralateral lobe for comparison.(h) Graph of relative enhancement versus time.ROi1 shows rapid enhancement with high peak relative enhancement and contrast washout in keeping with cancer.In comparison ROi2 in the contralateral lobe has gradual enhancement with low peak relative enhancement and no significant contrast washout in keeping with benign PZ.

Figure 3 .
Figure 3.A 60-yr-old asymptomatic man with raised PSA on health screening.TRUS biopsy confirmed prostatic acinar adenocarcinoma, Gleason grade 3 +4=7 (a) Axial T1WI shows diffuse hyperintensity in the PZ and right central gland consistent with post biopsy haemorrhage.(b) Axial T2WI shows several hypointense foci in the PZ, more on the right, with irregularity of the prostate capsule.This corresponds to areas of haemorrhage seen on T1WI, mimicking carcinoma.However a small focus of relatively lower signal intensity is seen anteriorly in the right PZ (arrow), this was noted to extend inferiorly to the prostate apex suspicious for cancer.(c) ADC map shows mild restricted diffusion of the haemorrhagic foci in the PZ.A small focus of more intense restricted diffusion anteriorly in the PZ (arrow) corresponds to the suspicious lesion seen on T2WI.(d) DCE-MRI, ROi1 has been placed on the suspicious lesion in the right anterior PZ, while ROi2-4 have been placed in the remaining PZ for comparison.(e) Graph of relative enhancement versus time.ROi1 enhancement curve shows rapid contrast enhancement with high peak relative enhancement and contrast washout in keeping with cancer.ROi2-4 show gradual contrast enhancement with low peak relative enhancement and no contrast washout in keeping with benign process.The patient had a radical prostatectomy and histology confirmed tumour involvement of both lobes with a tumour volume of 15%.The remnant sites of tumour are probably obscured by post biopsy haemorrhage on MRI.

Figure 4 .
Figure 4. 57-yr-old man with gross haematuria and lower urinary tract symptoms.Cystoscopy and biopsy confirmed prostatic adenocarcinoma, Gleason grade 4+4=8.(a)Axial T2WI shows large prostate cancer of the left lobe with extracapsular tumour infiltration.Posteriorly there is loss of fat plane with the rectum with soft tissue stranding of the mesorectum (arrow) in keeping with rectal serosal infiltration.Anteriorly tumour infiltration of the venous plexus on the left is seen.(b) Axial T2WI shows large tumour mass invading the left neurovascular bundle, note normal neurovascular bundle on the right (arrow).(c)Axial T2WI shows tumour invasion of both seminal vesicles, more on the left, with nodular tumour infiltration of the mesorectal fascia (arrow).(d) Sagittal T2WI shows thickening and abnormal signal of the bladder neck in keeping with tumour invasion (arrow).(e) Coronal T2WI shows tumour indenting the left levator ani which is thickened with abnormal hyperintenisty in keeping with tumour infiltration (arrow).(f)Axial T2WI of the pelvic inlet shows bilateral hydroureters (arrows) secondary to tumour involvement of both vesicoureteric junctions.