Key words
multiparametric MRI - prostate carcinoma - prostatitis - prostatic artery embolization
- prostate enlargement - prostatic anomalies
Introduction
In recent years, multiparametric MRI of the prostate (mpMRI) has successively been
implemented in the process of clinically significant prostate cancer detection [1], active surveillance [2], and relapse diagnosis [3]. National and international guidelines recommend mpMRI in combination with consecutive
MRI-guided targeted and systematic biopsy in order to minimize false-negative results
in biopsy-naïve patients [4]. There is also consensus for the indication of mpMRI prior to targeted biopsy after
previous negative systematic biopsy and prior to placing a patient under active surveillance
[4]
[5]
[6]. Further indications for mpMRI are the evaluation of local tumor expansion and extraprostatic
infiltration, staging of high-risk tumors prior to therapy [5], evaluation of tumor extent prior to focal therapy [5] and image-guided radiotherapy [IGRT] [7]. The diagnostic accuracy of mpMRI for the detection of clinically significant cancer
has been extensively studied. A recent meta-analysis reports a pooled sensitivity
of 87 % and a pooled specificity of 74 % for the standardized reporting lexicon for
mpMRI [8], PI-RADS (prostate imaging reporting and data system), with version 2.1 being the
most recent edition [9].
Despite this major field of application, prostate MRI can be employed as a diagnostic
modality for various other, benign conditions. In this review, we provide an overview
of the use of prostate MRI for enlarged prostate imaging, prostate artery embolization
imaging, prostatitis imaging, and imaging of congenital anomalies. If applicable,
we refer to recommendations of (German) national guidelines and international guidelines
(EAU and AUA). We do not review the imaging of malignancies other than adenocarcinoma
as these entities have been discussed in detail before [10].
Imaging the enlarged prostate
Imaging the enlarged prostate
Definitions and guidelines for imaging
In this manuscript, we follow the terminology used in the German S2e guideline “Diagnostic
and differential diagnosis of benign prostate syndrome (BPS)”. An update of the guideline
is currently in progress. The term benign prostate syndrome (BPS) refers to the triad
of lower urinary tract symptoms (LUTS), benign prostatic enlargement (BPE), and bladder
outlet obstruction (BOO) [11]. BPE is defined as an increase in prostate volume (> 25 ml, although different cut-off
values have been proposed) due to benign prostatic hyperplasia (BPH). BPH is a histopathological
diagnosis and is commonly used incorrectly synonymously with BPS, although only 25–50 %
of patients with BPH will eventually develop LUTS over time. Additionally, BPH is
often used incorrectly for an enlarged prostate diagnosed with imaging alone. BOO
is defined as a reduced rate of urine flow and an increase in detrusor pressure, irrespective
of cause [12]. Benign prostatic obstruction (BPO) represents BOO due to BPE [13].
LUTS comprise both irritative symptoms such as high frequency of urination or urge
incontinence and obstructive symptoms like decreased peak urine velocity or terminal
dribbling. LUTS can be caused by pathologies other than BPE/BOO, e. g. by infection,
structural anatomical aberrations or neurogenic disorders. For a comprehensive review
of LUTS, refer to the guidelines of the National Institute for Health and Care Excellence
(NICE) [14]. English-speaking countries specify the diagnosis of LUTS due to BOO on the basis
of BPO/BPE by referring to “LUTS suggestive of BPH” [11]
[12]. Only in 50 % of cases will BPH eventually result in BPE [14]. On the other hand, BPE is not a necessary condition for BPO (patients with small
prostates may suffer from symptoms due to musculostromal hyperplasia) [15].
Typical indications for imaging in the assessment of BPS are measurement of prostate
size and examination of the presence of an intravesical prostatic lobe, for which
guidelines suggest transrectal (TRUS) or transabdominal suprapubic ultrasound [13]. It is explicitly stated that cross-sectional imaging can be employed when already
available [12]. However, the acquisition of new cross-sectional images of the prostate is currently
not implemented in the diagnostic algorithm of LUTS/BPS [12].
MRI offers excellent soft tissue contrast and different prostatic zones can be reliably
distinguished and accurately measured [16]. Quantification of the exact prostate volume, exclusion of prostate cancer prior
to therapy of an enlarged prostate and detection of pathologies leading to LUTS are
promising use cases for mpMRI that have not yet been implemented in current guidelines.
It is recommended to estimate prostate volume by measurement of the maximum longitudinal
and anterior-posterior diameter on a mid-sagittal image and measurement of the maximum
transverse diameter on axial images with the ellipsoid formula (D1 × D2 × D3 × 0.52)
[9]. Furthermore, manual and automated segmentation [17] may be employed.
Classification of phenotype
The zonal anatomy of the prostate (differentiating transition zone, peripheral zone,
central zone, periurethral glands, and anterior fibromuscular stroma) has been established
by McNeal [18]. In the case of an enlarged prostate, Wasserman proposed a phenotypical classification,
taking into account in which part (or combination of parts) the enlargement originates
[15]. The MRI classification [15] is based on an ultrasound classification [19]. Subtypes of BPH phenotypes may lead to specific symptoms – the AUA has suggested
additional research in “disease ‘phenotypesʼ and […] better disease definitions (e. g. […] patient phenotypes relative to urologic symptom profiles)” [15]. We provide an overview of proposed phenotypes in [Fig. 1]. The reported distribution of Wasserman types was 63 % type 1 and 31 % type 3 (after
exclusion of type 0 cases) in Wasserman et al. 2015 [15]. According to the authors and to our own clinical experience, Wasserman type 2 occurs
more infrequently. The majority of patients can thus be described with only two phenotypes,
compare to [Fig. 2]. When enlarged, the transition zone is referred to as lateral lobes and the periurethral
glands as the median (retrourethral) lobe [19].
Fig. 1 Wasserman classification of prostate phenotypes. Green: normal prostatic contour,
red: urethra, brown: trigone. a type 0: volume ≤ 25 ml, little/no zonal enlargement. b Type 1: bilateral transition zone enlargement (blue). When large, the urethra is
displaced posteriorly. c Type 2: retrourethral lobe enlargement. When large, the proximal urethra is displaced
anteriorly. The trigone is elevated. d Type 3: combination of type 1 and type 2. e Type 4: pedunculated, hyperplastic tissue that arises from the submucosa of the urethra
and protrudes into the bladder. The trigone is not elevated (Type 5: type 4 + either
type 1 or type 2, not shown). f Type 6: subtrigonal ectopic hyperplasia. All other combinations/patterns are assigned
type 7.
Abb. 1 Phänotypische Klassifikation der Prostata nach Wassermann. Grün: normale Kontur der
Prostata, rot: Urethra, braun: Trigonum. a Typ 0: Volumen ≤ 25 ml, kaum/keine zonale Vergrößerung. b Typ 1: bilaterale Vergrößerung der Transitionszone (blau). Bei höhergradiger Vergrößerung
dorsale Verlagerung der Urethra. c Typ 2: Vergrößerung des retrourethralen Lobus. Bei höhergradiger Vergrößerung anteriore
Verlagerung der Urethra. Anhebung des Trigonums. d Typ 3: Kombination der Typen 1 und 2. e Typ 4: gestieltes, hyperplastisches Gewebe mit Ursprung aus den submukösen Anteilen
der Urethra mit Protrusion in die Harnblase. Keine Anhebung des Trigonums (Typ 5:
Typ 4 + entweder Typ 1 oder Typ 2, nicht abgebildet). f Typ 6: Subtrigonale ektope Hyperplasie. Alle anderen Kombinationen werden als Typ
7 subsummiert.
Fig. 2 a Wasserman prostate type 1, enlargement of the transition zone only. b Wasserman prostate type 2, enlargement of the retrourethral lobe only. c Wasserman prostate type 3, enlargement of the transition zone and the retrourethral
lobe. The majority of patients will either have a type 1 or type 3 phenotype.
Abb. 2 a Typ 1 nach Wassermann, ausschließlich Vergrößerung der Transitionszone. b Typ 2 nach Wassermann, ausschließlich Vergrößerung des retrourethralen Lobus. c Typ 3 nach Wassermann, Vergrößerung der Transitionszone und des retrourethralen Lobus.
Typ 1 und Typ 3 stellen die am häufigsten vorkommenden Ausprägungstypen dar.
Two different tissues contribute to hyperplasia of the prostate and therefore to symptoms
of BOO on the basis of BPH: glandular/epithelial tissue and stromal tissue [19]. Predominant hyperplasia of glandular tissue leads to mechanical compression of
the urethra and the bladder neck, referred to as the static effect. Hyperplasia of
stromal tissue leads to an increase in muscle tone, referred to as the dynamic effect
[19]. There is evidence that MRI can distinguish between these forms of hyperplasia,
with epithelial hyperplastic changes having a high signal in T2-weighted images and
stromal hyperplastic changes having a low signal [20], refer to [Fig. 3]. Although this knowledge could hypothetically influence treatment options (e. g.,
better response to α1-receptor antagonists in cases with predominantly stromal hyperplasia),
this approach has not been sufficiently investigated.
Fig. 3 a Axial T2w. b Coronal T2w. Glandular hyperplastic changes of the transition zone have high signal
intensity (solid arrows), stromal hyperplastic changes have low signal intensity (dashed
arrows).
Abb. 3 a Axiale T2w. b Koronare T2w. Glanduläre hyperplastische Veränderungen der Transitionszone zeigen
eine hohe Signalintensität (durchgezogene Pfeile), stromale hyperplastische Veränderungen
zeigen eine niedrige Signalintensität (gestrichelte Pfeile).
Over the past two decades, an intravesical protrusion of enlarged prostatic tissue
has been proven to be a clinically relevant morphological feature [21]. For example, a trial without a catheter in the case of acute urinary retention
related to BPE is more likely to fail when intravesical protrusion is > 10 mm [22]. The extent of intravesical protrusion (> 10 mm versus ≤ 10 mm) is correlated with
the severity of BOO in cases with BPE [23], compare to [Fig. 4a]. A protrusion > 10 mm also predicts poorer response to treatment with tamsulosin
in patients with LUTS due to BPO compared to patients with a protrusion ≤ 10 mm [24]. Measurement of intravesical prostatic protrusion (IPP) is mentioned in the current
EAU guideline [13] as a potentially “feasible option to infer BPO in men with LUTS”, and “the role of IPP as a noninvasive alternative to pressure flow studies (PFS) in the
assessment of male LUTS remains under evaluation”
[13]. AUA guidelines refer to ultrasound-based evaluation of IPP as optional during the
clinical workup [12].
Fig. 4 a Intravesical prostatic protrusion (IPP, dashed line) is measured perpendicular from
the assumed normal bladder floor (white line) on a mid-sagittal image. b The prostatic urethral angle (PUA) is the angle between the proximal and distal part
of the prostatic urethra (white lines) measured on a mid-sagittal image.
Abb. 4 a Intravesikale Protrusion der Prostata (IPP, gestrichelte Linie) wird rechtwinklig
zur erwarteten physiologischen Ebene des Harnblasenbodens (durchgezogene Linie) gemessen.
b Der intraprostatische Winkel der Urethra (PUA) beschreibt den Winkel zwischen proximalem
und distalem Abschnitt der prostatischen Urethra (durchgezogene Linie) in der paramedianen
Sagittalebene.
Several studies investigated the correlation of the prostatic urethral angle (PUA)
with symptoms due to BOO/LUTS in cases with BPE. PUA is defined as the angle between
the proximal and distal part of the prostatic urethra measured on a mid-sagittal image,
compare to [Fig. 4b]. The angulation point is the proximal part of the verumontanum [25]. A common quantification tool for the severity of symptoms in BPS is the international
prostatic symptoms score (IPSS). Two studies that assessed PUA in MRI (mid-sagittal
T2-weighted images) did not demonstrate a significant correlation of PUA with the
IPSS score [26] – with one study acknowledging the usage of an endorectal coil as a possible source
of bias due to deformation of the prostate and the prostatic urethra [27]. Other studies using ultrasound as imaging modality reported significant associations
of PUA with IPSS, BOO severity, and peak urine flow rate [25]
[28]
[29]. A commonly reported cut-off value for an increased PUA is ≥ 35° [25]. PUA measurement is mentioned in the EAU guidelines as an experimental diagnostic
tool for noninvasive pressure-flow testing [13]. However, there is also a strong recommendation not to offer noninvasive testing
as an alternative to PFS for the diagnosis of BOO.
MRI of the prostate before and after prostatic artery embolization
MRI of the prostate before and after prostatic artery embolization
Performing multiparametric MRI of the prostate before a planned prostatic artery embolization
(PAE) serves to detect clinically significant prostate cancer, to determine the size
of the prostate, and to visualize the zonal anatomy. Preprocedural imaging of the
prostatic arteries helps interventional radiologists to reduce procedure time and
the risk of embolization of surrounding organs [30]. Vessel imaging can be performed with DSA combined with cone-beam CT, CT angiography,
or MR angiography [30]
[31]
[32].
If there are PI-RADS 3–5 findings in the patient's prostate, these have to be clarified
before PAE by biopsy. The size of the prostate and certain characteristics of the
zonal anatomy are prognostic factors for the clinical success of PAE, which should
be addressed in the pre-procedure informed consent discussion. The larger the total
prostate and the transition zone, the better the clinical success [33]. With an ROC analysis, a threshold value of 39 mL for the total prostate volume
was calculated as a guide for a minimum size of the prostate to be treated [33]. Patients with a dominant transition zone and large BPH nodes benefit more from
PAE than patients without a dominant transition zone and large BPH nodes [34]. The calculation of the quotient of transition zone volume/total prostate volume
showed better clinical success for values > 0.45 with a sensitivity of 85 % and a
specificity of 75 % [35]. It was also shown that the size of the median lobe is positively correlated with
the clinical success of PAE [36]. IPP is significantly reduced by PAE [37]. Measurement of IPP and PUA is mentioned in the current position paper of the German
Society of Interventional Radiology (DeGIR) on PAE in the pre-procedure evaluation.
Measurement in follow-up exams is possible in the case of special interest [38].
One day after PAE the anatomy in the transition zone can be delineated more poorly
on T2w images than before PAE [39]. In addition, T1w hyperintensities are found as surrogate markers for hemorrhagic
necrosis in almost half of cases [39]. Furthermore, the diffusion-weighted and the DCE-MRI images show further signs of
ischemia with diffusion restriction and severely reduced vascularization [39], compare to [Fig. 5]. 6 months after PAE, the changes seen in the diffusion-weighted and DCE-MRI images
are less distinct and signs of fibrotic remodeling, especially of the transition zone,
can be found on T2w images [39]. Parameters that enable an inference from the initial MRI changes 1 day after PAE
to the clinical outcome could not be identified [39]. However, another study showed that 87 % of patients with clinical success of PAE
had ischemic areas on DCI-MRI images [40]. Furthermore, when evaluating an MRI examination of the prostate after PAE, the
continually decreasing volume of the prostate after successful embolization should
be taken into account and seems to have reached the nadir after 6 months [41]. After 12 months, morphological stability is reached [38]. The DeGIR position paper states useful clinical control intervals of 1–3 months,
6 months, and 12 months after PAE. In the post-procedural setting, MRI is an option
to control treatment success [38].
Fig. 5 mpMRI of the prostate before PAE (top row) and 1 day after PAE (second row): On the
morphological T2w images (column 1), the anatomy of the transition zone 1 day after
PAE is more poorly delineated compared to the pre-PAE images. On the diffusion-weighted
images (columns 2 and 3), diffusion restriction after PAE is visible as a surrogate
marker for cytotoxic edema. On the pharmacokinetic parameter map (kep; calculated
from the signal intensities of DCE-MRI; column 4), the surrogate parameter kep decreases
significantly as a sign of reduced vascularization 1 day after PAE.
Abb. 5 Multiparametrische MRT der Prostata vor PAE (obere Reihe) und einen Tag nach PAE
(untere Reihe): Die anatomischen T2w-Sequenzen (erste Spalte) zeigen posttherapeutisch
eine unschärfere Demarkierung und Berandung der Transitionszone. Deutlich progrediente
Diffusionsrestriktion in den diffusionsgewichteten Sequenzen (zweite und dritte Spalte)
als Surrogatparameter für ein zytotoxisches Ödem. Das pharmacokinetic parameter mapping
(kep; errechnet aus den Signalintensitäten der dynamischen Kontrastmittelsequenzen;
vierte Spalte) als Surrogatparameter für Vaskularisation ist einen Tag posttherapeutisch
deutlich regredient.
Imaging in prostatitis
Prostatitis can be divided into three subgroups according to symptoms and etiology.
Patients with acute bacterial prostatitis (ABP) usually suffer from abruptly-onsetting
voiding symptoms, diffuse perineal pain (which may be associated with defecation)
and fever. Chronic bacterial prostatitis (CBP) is defined by pain in the perineal
region for a period of three months or more. Lastly, chronic pelvic pain syndrome
(CPPS) describes a non-bacterial form of chronic prostatitis with similar symptoms
[42].
European guidelines recommend distinguishing bacterial prostatitis from CPPS according
to the National Institute of Diabetes, Digestive and Kidney diseases (NIDDK) and National
Institutes of Health (NIH) classification [43]. Although it is a very common diagnosis, bacterial infection is only proven in around
10 % of prostatitis cases [44]. E. coli are the predominant pathogens in patients with acute bacterial prostatitis
[45]. Chronic bacterial prostatitis is caused by a wider spectrum of pathogens, including
atypical bacteria. One study found that in 74.2 % of patients with symptoms of chronic
prostatitis there was an underlying infectious etiology. Although E. coli is often
regarded as the most common pathogen, the authors found infections with C. trachomatis
in 37.2 %, T. vaginalis in 10.5 % and U. urealyticum in 5 % of the cases, whereas
E. coli accounted for only 6.6 % [46]. CPPS per definition is an abacterical condition with a mostly unknown etiology
with immunological dysfunction, neuropathic pain, and difficult to detect infections
such as interstitial cystitis, as well as other possibilities being discussed.
There are no recommendations on a standardized diagnostic algorithm, but the diagnostic
basis consists of urine dipstick testing (U-Stix), mid-stream urine culture, and DRE
[47]. Dipstick testing for nitrite and leukocytes has a positive predictive value of
95 % and a negative predictive value of 70 % in patients with ABP [48]. On DRE, the prostate may appear swollen and tender. Additionally, blood cultures
in the case of fever and prostate-specific antigen levels can be taken into consideration.
When testing for CBP, the four-glass Meares and Stamey test is established as the
diagnostic tool of choice [49]. It is furthermore suggested to take urethral samples in order to rule out atypical
pathogens such as C. trachomatis and others [46].
Transrectal ultrasound (TRUS) can be helpful to detect complications such as endoprostatic
abscesses but is not recommended as a first-line diagnostic tool for prostatitis due
to its limited sensitivity [50]. PSA levels are only increased in 60 % of ABP and 20 % of CBP and therefore offer
“no practical diagnostic information in prostatitis” [51]. In MR imaging, prostatitis can occur as a focal or diffuse pattern of low T2 signal
intensity with low to moderate diffusion restriction and corresponding early avid
contrast enhancement [52]. [Fig. 6] provides an example case of ABP. First-line therapy consists of oral application
of culture-guided antibiotic treatment. In cases of ABP an empirical regiment until
pathogen identification or parenteral antibiotic treatment of systemically-ill patients
can be considered [53].
Fig. 6 28-year-old patient with acute bacterial prostatitis. The patient suffers from perineal
pain and tenderness in the digital rectal examination. PSA level is 12.2 ng/ml. MRI
is performed to exclude complications. The peripheral zone shows diffuse decreased
signal intensity on T2w (a), diffuse avid contrast agent uptake (b), and diffusely restricted diffusion on diffusion-weighted images (c, d). No focal lesion is observed, an abscess is excluded. Three weeks after treatment
with antibiotics, clinical symptoms improved and PSA was 6 ng/ml.
Abb. 6 28-jähriger Patient mit akut bakterieller Prostatitis. Er wurde mit perinealen Schmerzen
und schmerzempfindlicher Prostata in der digital rektalen Untersuchung vorstellig.
Der PSA-Wert betrug 12.2 ng/ml. Es erfolgte eine MRT zum Ausschluss von Komplikationen.
Es zeigte sich eine diffuse Signalabsenkung der peripheren Zone in T2w (a) sowie diffuse Kontrastmittelaufnahme (b) und diffuse Diffusionsrestriktion in den diffusionsgewichteten Sequenzen (c, d). Kein Nachweis von fokalen Läsionen oder intraprostatischen Abszessen. Befundverbesserung
und PSA-Abfall nach dreiwöchiger Antibiotikatherapie.
Prostatic abscesses are severe complications in prostatitis and, according to EAU
guidelines, can be detected by TRUS or “imaging studies”, thus including MRI. Vice versa, prostatic microabscesses can indicate prostatitis
when other imaging criteria are missing. Similar to manifestations in other locations,
endoprostatic abscesses appear as mostly circumscribed lesions with a T2w-hyperintense
signal, peripheral contrast enhancement, and diffusion restriction [54], compare to [Fig. 7]. Treatment can either be conservative when abscesses remain under 1 cm in diameter
or interventional (e. g. aspiration, drainage) in the case of greater abscesses [55].
Fig. 7 50-year-old patient with Klebsiella pneumonia sepsis. The patient suffers from pelvic
pain, MRI is performed to evaluate possible foci of inflammation. In the prostate,
large fluid collections (T2w, a, arrows) are observed bilaterally. There is rim-like contrast enhancement, consistent
with abscesses (b).
Abb. 7 50-jähriger Patient mit Klebsiella pneumonia-Sepsis. Der Patient wurde vorstellig
mit pelviner Schmerzsymptomatik, in diesem Rahmen Durchfühung einer MRT zum Ausschluss
eines Infektfokus. Es imponierten intraprostatische Flüssigkeitskollektionen bilateral
(T2w, a, Pfeile). Zudem randständiges Kontrastmittelenhancement, passend zu Abszessformationen
(b).
Granulomatous prostatitis [GP] is a rare type of prostatic inflammation (1–3 % of
cases of benign prostatic inflammation) due to a variety of causes. While primary
GP is often idiopathic, secondary causes may be urinary tract infections, surgical
interventions, biopsy, and BCG instillation – an established treatment option for
superficial urothelial bladder carcinoma. When dealing with nonspecific GP, which
represents most cases, the disease is mainly self-limiting and requires only symptomatic
treatment [56]
[57]
[58]. GP occurs both in young and old patients, with the greatest prevalence between
50–70 years and a mean age of 62–63 years [59]
[60]. Incidence rates of prostatitis are highest between the third and fifth decades
of life and from the seventh decade onwards [61]. Imaging shows either a diffuse or nodular low T2 signal compared to normal tissue,
sometimes with extracapsular extensions, diffusion restriction, and early, often prolonged
peripheral contrast enhancement [57]
[62], compare to [Fig. 8]. Histopathologically, lesions appear as centrally caseating necrosis corresponding
to low signal intensities in the center of the lesions in post-contrast imaging [62]. Small cystic components within the lesions are described in a few cases. The disease
can be barely distinguishable from malignancies as radiological features are overlapping
[57]. Hence, follow-up examinations and histopathological confirmation through biopsy
in unclear cases to rule out PCa appear to be adequate diagnostic pathways, although
guidelines do not offer specific recommendations.
Fig. 8 59-year-old patient with a proven Gleason 7a tumor is referred to prostate MRI for
local staging. PSA is 6 ng/ml. A lesion with low signal in T2w (a) and restricted diffusion (b) is observed in the posterolateral left peripheral zone (solid arrows in a and b), corresponding to the known adenocarcinoma. Incidentally, an exophytic lesion is
observed in the urinary bladder (solid arrow in c, T2w image), suspicious for transition cell cancer (TCC). This is proven histopathologically,
and the TCC is treated with resection and BCG instillation. In a follow-up MRI eight
months later, there are multiple new lesions visible in the prostate which show markedly
restricted diffusion (e, dashed arrow, ADC map and corresponding T2w, d) with rim-like enhancement (f, dashed arrows). This is consistent with the diagnosis of granulomatous prostatitis.
Abb. 8 MRT eines 59-jährigen Patienten mit gesichertem Gleason-7a-Tumor im Rahmen des Stagings.
Der PSA-Wert betrug 6 ng/ml. Es imponiert eine T2w-hypointense Läsion (a) mit Diffusionsrestriktion (b) in der posterolateralen peripheren Zone links (durchgezogene Pfeile in a und b), entsprechend dem bekannten Karzinomfokus. Zudem inzidenteller Befund einer exophytischen
Läsion der Harnblase (durchgezogene Pfeile in c, T2w) mit Verdacht auf ein Transitionszellkarzinom (TCC). Das Karzinom wurde histopathologisch
bestätigt, hiernach Resektion und BCG-Instillation. Eine Kontrolle mittels MRT 8 Monate
später zeigt mehrere neue intraprostatische Läsionen mit Diffusionsrestriktion (e, gestrichelte Pfeile. f randständige Kontrastmittelaufnahme), passend zu der Diagnose einer granulomatösen
Prostatitis.
Although mpMRI has a high sensitivity for prostate cancer detection, it sometimes
lacks specificity, partly due to the above-mentioned conditions. A recent study found
that quantitative imaging analysis of mpMRI could reliably differentiate prostatitis,
which represents the non-neoplastic condition with imaging features closest to those
of prostate cancer, from prostate cancer [63]. It is stated that the combination of several quantitative imaging parameters, among
other apparent diffusion coefficient (ADC) values, pharmacokinetic parameters, and
time to peak (TTP) enhancement can achieve a total overall diagnostic accuracy of
92.7 %. Also, signal intensity–time curves may help distinguish between the two conditions.
Congenital anomalies of the prostate
Congenital anomalies of the prostate
The prostate gland and the bulbourethral glands develop from the urogenital sinus,
whereas the seminal vesicles (SV) and the ejaculatory duct (ED) arise from the Wolffian
ducts. There are no guidelines (EAU, AUA) for the evaluation of prostatic congenital
anomalies. Imaging in those cases remains a physician’s individual decision.
Congenital anatomic anomalies of the prostate gland such as agenesis, hypoplasia,
cysts and ectopia are rare conditions. Just like anomalies of the seminal vesicles,
they often appear in combination with other anomalies of the urogenital system [64]. For example, agenesis of the prostate gland can be associated with testicular feminization,
ambiguous genitalia, epispadias or hypospadias ([Fig. 9]).
Fig. 9 30-year-old patient with erectile dysfunction and suspected dysplasia of the prostate
gland and the SV. MRI shows aplasia of the prostate gland and hypoplasia of the SV
(not fully depicted). Right testicle was removed after a fulminant epididymis infection
during childhood, left testicle was hypoplastic (8 ml). Additionally, the patient
presented with penile hypospadias. PSA levels were as low as 0.04 ng/ml which suggests
that remnants of the prostate gland, not detectable by MRI, may persist. a T2w sagittal plane. b T2w axial plane.
Abb. 9 30-jähriger Patient mit erektiler Dysfunktion und Verdacht auf Dysplasie der Prostata
und Samenblasen. Die MRT zeigt sowohl eine Prostataaplasie als auch eine Hypoplasie
der Samenblasen (nicht vollständig dargestellt). Entfernung des rechten Hodens nach
fulminanter Epididymidis in der Kindheit, der verbliebene linke Hoden imponierte mit
8 ml Volumen hypoplastisch. Zudem imponierte eine Hypospadie in der klinischen Untersuchung.
Der PSA-Wert war mit 0.04 ng/ml deutlich erniedrigt, möglicherweise im Rahmen residueller,
nicht mittels MRT erfassbarer Drüsenanteile. a T2w sagittale Ebene. b T2w axiale Ebene.
Congenital prostatic cysts originate from either the Müllerian or the Wolffian duct.
Anomalies originating from the Müllerian duct are utricular cysts and Müllerian duct
cysts, usually located in the prostatic midline. ED and SV cysts on the other hand
arise from the Wolffian duct and mostly occur off-midline. ED and SV cysts represent
rather uncommon conditions and shall not be discussed further in this article. Another
pathology associated with the Wolffian duct is Zinner’s syndrome (ipsilateral ejaculatory
duct obstruction, seminal vesicle cysts, and renal agenesis). For further details
on the differential diagnosis (including periprostatic lesions like Cowper’s duct
cysts) of prostatic cystic lesions, refer to [65].
Utricular cysts are focal, often pear-shaped dilatations within the prostatic utricle
(a remnant of the Müllerian duct) and therefore show continuity with the pars prostatica
of the urethra. They are located in a median plane within the prostatic gland, compare
to [Fig. 10]. Müllerian duct cysts (results of failed focal regression of the Müllerian duct)
show no communication with the prostatic urethra, may extend beyond the prostate gland,
can grow to large diameters with consecutive irritative urinary symptoms, and typically
arise behind the Colliculus seminalis. Utricular cysts and Müllerian duct cysts may
be indistinguishable on imaging. Whereas utricular cysts are associated with various
genitourinary abnormalities, Müllerian duct cysts usually appear without such associations
[65]. Rarely, the otherwise incidental findings may become symptomatic due to infection,
urinary retention, bleeding, and impaired fertility [10]. In those cases, MRI of the prostate can be employed for visualization of complex
anatomical variants and offers additional information.
Fig. 10 57-year-old patient with utricular cyst as a secondary finding while evaluation for
prostate cancer. a T2w sagittal plane. b T2w axial plane.
Abb. 10 57-jähriger Patient mit Utriculuszyste als Nebenbefund im Rahmen der Detektion eines
Prostatakarzinoms. a T2w sagittale Ebene, b T2w axiale Ebene.
In contrast to neoplasms and abscesses, benign cystic lesions show a homogeneous T2
hyperintense signal, a simple internal structure, and no restriction in diffusion-weighted
imaging.
Summary
In addition to the detection of clinically significant cancer, prostate MRI can be
utilized to obtain information for a variety of benign disorders. In this review,
we discuss the use of prostate MRI for imaging of the enlarged prostate, imaging related
to prostatic artery embolization, and imaging in prostatitis. We also briefly address
imaging in congenital anomalies. Especially in the workup of an enlarged prostate
and prostatitis, prostate MRI does not play a central role at the moment according
to EAU and AUA guidelines. However, we believe that additional knowledge of clinically
significant findings unrelated to established indications for MRI examinations offers
additional value for patient care.
