Keywords
benign - prostate - seminal vesicles - magnetic resonance imaging - MRI
Introduction
Non-malignant conditions of the prostate and seminal vesicles (SVs) are common in
clinical practice and often detected incidentally while reporting imaging studies.
These include age-related changes such as benign prostatic hyperplasia, congenital
and acquired prostatic and periprostatic cysts, infective and inflammatory changes
in the prostate, and benign neoplasms. In multi-parametric MRI (mpMRI) of the prostate,
many of these entities contribute significantly to pitfalls in image interpretation.
This leads to both false positive and false negative diagnoses of clinically significant
prostate cancer.[1]
[2]
[3]
[4] Knowledge of their clinical presentation and imaging appearances can help accurate
image interpretation and guide clinical referrers to optimal management. In this review,
we present common non-malignant pathologies of the prostate and SVs and discuss the
clinical presentation and their imaging appearances in different imaging modalities.
Benign Prostatic Hyperplasia
Benign Prostatic Hyperplasia
Benign prostatic hyperplasia (BPH) refers to an increase in the number of prostatic
stromal and epithelial cells in the transition zone (TZ) and periurethral glands that
cause the formation of discrete nodules and prostate enlargement.[5] It develops in response to testosterone after it is converted to dihydrotestosterone.[6] Its prevalence increases with age and affects approximately 75% of men older than
70 years.[5] BPH can cause bladder outlet obstruction leading to lower urinary tract symptoms
like urgency, frequency, weak stream, and nocturia.
Imaging modalities in BPH include transabdominal ultrasound, transrectal ultrasound
(TRUS), and MRI. Computed tomography (CT) scan has limited value as it does not accurately
define prostatic zonal anatomy. Transabdominal ultrasound is the standard first-line
investigation for BPH and shows an increase in a prostate volume exceeding 25cc. The
central gland is enlarged with hypoechoic or mixed echogenicity. There may be significant
postvoid residual urine and associated bladder wall hypertrophy and trabeculations
due to chronic bladder outflow obstruction.
On TRUS, BPH appears as a diffuse or nodular enlargement of the TZ, periurethral glandular
tissue, or both.[7] Hyperplastic nodules are usually hypoechoic to peripheral zone (PZ) tissue but may
be isoechoic or hyperechoic depending on the amount of fibrous, muscular, and glandular
hyperplastic elements and are surrounded by fibrous envelopes that appear as hypoechoic
rims ([Fig. 1]).[7] On MRI, BPH appears as band-like areas and/or encapsulated circumscribed round nodules
in the TZ. While predominantly glandular nodules appear T2 hyperintense, stromal nodules
may appear T2 hypointense and contribute to a substantial number of PIRADS 3 lesions
in clinical practice.[6] The heterogeneous appearance of TZ on T2 due to both hyperintense and hypointense
BPH nodules is likened to “organized chaos” ([Fig. 2]). BPH nodules showing complete T2 hypointense rim are categorized as typical BPH
nodules (PIRADS 1), while those showing partial encapsulation are atypical nodules
(PIRADS 2). Diffusion-weighted imaging (DWI) helps in differentiating BPH nodules
from prostate cancer, as they do not show marked restricted diffusion on high b Value
DWI (b≥ 1400) or marked hypointensity on apparent diffusion coefficient (ADC) images.
On dynamic contrast-enhanced MRI (DCE-MRI), BPH nodules may show early enhancement,
hence it is unreliable. Although BPH nodules typically occur in TZ, exophytic or extruded
BPH nodules can be seen in the peripheral zone ([Fig. 3]) or central zone[3] and share a similar MRI appearance. [Table 1] shows the types of BPH based on ultrasound and MRI findings.
Fig. 1 A 73-year-old man with lower urinary tract symptoms. Axial (A) and sagittal (B) transrectal ultrasound images showing enlargement of the bilateral transition zone
with heteroechoic benign prostatic hyperplasia nodules (arrowheads).
Fig. 2 A 66-year-old male with lower urinary tract symptoms. T2 image in the axial plane
(A) showing an enlarged transition zone with few well-encapsulated (arrowhead) and partly
encapsulated (arrow) benign prostatic hyperplasia nodules. These nodules can be hyperintense
if the glandular element predominates or hypointense if the stromal element predominates.
The admixture of these nodules creates an “organized chaos” pattern. Diffusion-weighted
imaging at b1500 (B) and apparent diffusion coefficient map (C) showing parts of this nodule showing restricted diffusion. Postcontrast image (D) showing early enhancement of these nodules.
Fig. 3 Extruded nodules in two different patients. Axial (A) and sagittal (B) T2-weighted magnetic resonance imaging (MRI) of the prostate in a 64-year-old man
with an enlarged prostate and raised prostate-specific antigen (9.65ng/mL) showing
benign prostatic hyperplasia (BPH) changes in the transition zone with retrourethral
protrusion into the bladder. There is an extruded BPH nodule seen in the left posteromedial
peripheral zone of the gland (arrowheads in A and B). Axial (C) and sagittal (D) T2-weighted
MRIs of the prostate in another 75-year-old male who had transurethral resection of
the prostate previously showing a well-encapsulated extruded heterogeneous nodule
in the central zone of the gland (white arrows).
Table 1
Classification of BPH based on ultrasound and MRI findings[8]
[9]
[10]
|
Type 0
|
Normal prostate with volume <25cc
|
|
Type 1
|
Bilateral TZ enlargement
|
|
Type 2
|
Retro urethral enlargement also called median lobe hypertrophy
|
|
Type 3
|
Bilateral TZ and retro urethral enlargement
|
|
Type 4
|
Pedunculated intravesical prostatic protrusion, enlarged single or multiple nodules
arising from intraluminal urethral submucosa
|
|
Type 5
|
Bilateral TZ and/or retro urethral enlargement with pedunculated intravesical protrusion
of prostate
|
|
Type 6
|
Sub trigonal or ectopic enlargement
|
|
Type 7
|
Other combination of enlargements
|
Abbreviations: BPH, benign prostatic hyperplasia; MRI, magnetic resonance imaging;
TZ, transition zone.
Early disease is managed conservatively with alpha-blockers and 5-alpha reductase
inhibitors. Surgical management for symptomatic patients is achieved with transurethral
resection of the prostate (TURP). Laser-based and thermal ablation procedures and
prostatic artery embolization may also reduce periurethral prostatic volume and obstruction.[8] Any procedure that does not completely remove the TZ has the potential for recurrence
and may result in the need for an additional procedure.
Infections and Inflammatory Diseases
Infections and Inflammatory Diseases
Prostatitis is inflammation or infection of the prostate and clinically presents with
symptoms referable to the lower urogenital tract and perineum. Studies suggest the
prevalence of prostatitis is 2 to 16%.[11] The National Institutes of Health classifies prostatitis into four categories—acute
bacterial prostatitis, chronic bacterial prostatitis, chronic prostatitis or pelvic
pain syndrome, and asymptomatic inflammatory prostatitis.[12]
Acute Prostatitis
Acute prostatitis has a bimodal age distribution affecting men of 20 to 40 years and
over 60 years.[13]
[14] The most common pathogen is Escherichia coli (in ∼60%), followed by Pseudomonas
aeruginosa and Enterococcus species.[15]
[16] The infection spreads as ascending urethral infection, direct seeding from prostatic
biopsy, intraprostatic reflux of infected urine, or by hematogenous spread as in sepsis
and tuberculosis. About 6% of acute bacterial prostatitis can progress to prostatic
abscesses in whom imaging is indicated.[17] Patients with acute prostatitis who do not respond to treatment after 48 hours should
be evaluated for a possible prostatic abscess.[18]
Prostatic abscess appears as a hypoechoic area with internal septae and thick well-defined
walls on TRUS ([Fig. 4]); TRUS is also of value in ultrasound-guided drainage of abscess (at least 18G needle
is preferred). Unroofing/transurethral drainage of the prostatic abscess is preferred
in lesions too large to drain percutaneously or lesions that do not respond to percutaneous
drainage.[19] Contrast-enhanced CT shows an edematous appearance of prostate and periprostatic
stranding. Prostatic abscess appears as hypodense focus with peripheral enhancement
and internal septations ([Fig. 5]).[20] Cross-sectional imaging also gives valuable information regarding extraprostatic
spread. MRI offers better soft tissue resolution than CT and is more sensitive than
TRUS in the early stages of abscess formation. Abscess shows a low signal on T1, high
signal on T2-weighted MRI, central diffusion restriction and displays peripheral rim
enhancement with gadolinium.[20]
Fig. 4 Transrectal ultrasound (TRUS) performed for a patient in sepsis shows enlarged prostate
with irregular hypo echoic area (A) representing abscess. There is hyper-vascularity
noted at the periphery of the gland (B) suggestive of prostatitis.
Fig. 5 A 61-year-old male with sepsis. (A, B) Axial computed tomography (CT) image showing irregular branching hypodense collections
in the prostate and seminal vesicles (arrowheads) with periprostatic fat stranding.
There is a contiguous thickening of the bladder base. (C) Selected high-resolution
CT images of the same patient showed multiple septic emboli in the lungs seen as cavitating
nodules (arrowhead).
Prostate must be carefully reviewed in patients with cystitis with persistent fever
in the absence of upper urinary tract infection (UTI), recurrent UTI in the absence
of renal involvement/structural abnormalities of the urinary tract, secondary peritonitis,
immunocompromised, diabetic patients, and those with sepsis ([Figs. 1] and [2]). Prostatic abscess carries high morbidity and mortality and needs a high index
of suspicion, and imaging is critical for timely diagnosis and treatment.
Chronic Prostatitis
It encompasses a spectrum of etiologies from a sequel to acute prostatitis, and recurrent
UTIs to IgG4-related disease and tuberculous prostatitis. Chronic prostatitis appears
as wedge-shaped T2 hypointense lesions with a linear pattern in the peripheral zone
with or without capsular retraction and does not show diffusion restriction ([Fig. 6]). Granulomatous prostatitis (GP) is a nodular form of chronic prostatitis. It can
be idiopathic, tuberculous, iatrogenic due to Bacille Calmette-Guerin (BCG) vaccine,
intravesical BCG for bladder cancer, postradiotherapy or due to autoimmune aetiologies
and systemic conditions like sarcoidosis.[21] GP demonstrates a tumor-like morphology, with nodular or diffuse hypoechogenic lesions
on ultrasound, and has PIRADS 5 appearance on mpMRI.[22] On T2-weighted MRI, GP lesions appear hypointense like prostate cancer. GP and cancer
lesions share high signal intensity on high b-value DWI and low signal intensity on
the ADC map. On DCE-MRI, GP shows moderate persistent enhancement and prostate cancer
shows early enhancement and rapid washout due to increased vascularity.[23] GP is more commonly diffuse when compared to prostate cancer. Unlike the diffuse
forms of prostate cancer, in GP the prostatic capsule is usually intact ([Fig. 7]). Clinical profile combined with declining serial prostate-specific antigen (PSA)
value in some cases may hint the radiologist to a diagnosis of GP over malignancy.
Fig. 6 A 65-year-old male with lower urinary tract symptoms, an enlarged prostate gland,
and a hard right-sided nodule palpable on clinical examination. Prostate-specific
antigen was 0.88 IU/mL. (A, B) High-resolution T2 axial and coronal images showed a wedge-shaped T2 hypointense
lesion with a striated appearance in the anterio–lateral and posterio–lateral peripheral
zone in the right mid-gland. (C, D) Diffusion-weighted imaging (b1500) and apparent diffusion coefficient map showed
no diffusion restriction. Based on these imaging features, magnetic resonance imaging
was reported as PIRADS 2, likely changes of chronic prostatitis.
Fig. 7 A 58-year-old male with prostate-specific antigen (PSA) of 5 IU/mL from elsewhere
and a repeat PSA at our center 8 weeks after the previous PSA of 1.64 IU/mL. Multi-parametric
magnetic resonance imaging (MRI) of the prostate was done. (A) T2-weighted axial image showed diffuse T2 hypointense signal of the prostate gland.
The capsule was smooth and there was no seminal vesicle involvement. (B, C) Diffusion-weighted imaging showed diffusely hyperintense prostate gland on b-1500
image and low signal on apparent diffusion coefficient map suggestive of diffusion
restriction. (D, E) Select images of dynamic contrast-enhanced MRI have shown diffuse intense enhancement
of the prostate gland. (F) Transrectal ultrasound -guided biopsy showed prostatic parenchyma with aggregates
of epithelioid histiocytes forming discrete granulomas (hematoxylin and eosin x 100).
Prostatic and Periprostatic Cysts and Their Mimics
Prostatic and Periprostatic Cysts and Their Mimics
Prostatic and periprostatic cysts are uncommon pathologies often encountered as incidental
findings on imaging.[24] These are mostly asymptomatic but sometimes may present with lower urinary tract
symptoms and infertility.[24] Knowledge of embryology and anatomical localization by high-resolution MRI helps
in characterizing these lesions.
Prostatic Utricle and Müllerian Duct Cysts
The Müllerian duct is an embryonic structure that normally regresses in males, except
for a part at its cephalic end that contributes to remnant structures such as the
prostatic utricle and testicular appendix.[25] A prostatic utricle cyst is a cystic dilatation of the prostatic utricle. Müllerian
duct cysts are cystic dilatations of segments of the Müllerian duct that failed to
regress.
Ultrasonography, CT, and MRI can detect these cysts. The anatomic location, shape
of the cyst, and relationship with the urethra can aid in distinguishing between prostatic
utricle cyst and Müllerian duct cyst as summarized in [Table 2]. MRI has the advantage of superior soft tissue resolution and high-resolution images
can assess relationships with adjacent structures better ([Fig. 8]).[26]
[27]
Table 2
Imaging differences between prostatic utricle cysts and Müllerian duct cysts
|
Prostatic utricle cyst
|
Müllerian duct cyst
|
|
Location
|
Always in midline location
|
Can extend to a slightly para-midline location
|
|
Extension above prostate
|
No
|
Yes
|
|
Communication with the urethra
|
shows communication with the urethra
|
no communication with the urethra
|
|
Configuration
|
Pear shape
|
Tear drop shape
|
|
Contents on aspiration
|
May contain sperms within
|
Sperms are not seen. However, occasionally contain calculi
|
Fig. 8 Prostatic utricle cyst in a 56-year-old man. Axial (A) and sagittal (B) high-resolution T2-weighted (T2W) magnetic resonance imaging (MRI) showing a midline
cystic lesion (arrowhead) at the level of verumontanum (arrowhead). (C, D) Müllerian duct cyst in a 37-year-old patient with recurrent urinary tract infections.
Axial (C) and sagittal (D) high-resolution T2W MRI showing a large, elongated midline hyperintense lesion(arrowhead)
extending above the prostate.
Management decisions are based on the size of the cyst, its location, and the symptoms
of the patient. Cysts larger than 2.5 cm are usually symptomatic and may need urology
referral and further management. These cysts can bleed or get secondary infection
and very rarely can transform into malignancy.[26] Management options for Müllerian duct cysts include surveillance, TRUS-guided aspiration
and injection of sclerosing agents, surgical excision, transurethral resection, and
percutaneous aspiration. Laparoscopic excision has also been tried.[24]
[27]
Ejaculatory duct cysts
Ejaculatory duct cysts usually develop secondary to ejaculatory duct obstruction[25] and can be congenital or acquired.[24] The ejaculatory duct is a short, approximately 2 cm long structure coursing through
the central zone of the prostate gland and formed by the joining of duct from the
SV and ductus deferens. On imaging, these are seen as paramedian cysts ([Fig. 9A, B]) in the central zone along the ejaculatory duct.[25] Larger lesions may extend above the prostate gland and appear as midline lesion.[25]
[26] The obstructed ejaculatory duct causes proximal dilatation of the duct depending
on the level of obstruction and extent of fibrosis. There can also be ipsilateral
prominence of vas deferens, dilatation of SV ducts, and enlargement of SV. High-resolution
MRI is helpful in localizing the level of obstruction.[25] Due to limited availability and cost factors, MRI is reserved for cases with inconclusive
ultrasonography.[25] Aspirate shows spermatozoa, and fructose and may rarely contain calculi.[26] The treatment is usually surveillance and surgery is considered in symptomatic patients
or those with infertility.
Fig. 9 Incidentally detected ejaculatory duct cyst in 48-year-old gentleman for the evaluation
of rectal polyp. Axial (A) and sagittal (B) high-resolution T2-weighted magnetic resonance imagings showing a left paramedian
cyst (arrowhead) in the central zone along the ejaculatory duct above the level of
verumontanum.
Prostatic retention cysts (PRC) and cystic degeneration of BPH
These are usually seen in the region of glandular tissues of the prostate gland, mostly
asymptomatic, and encountered during the 5th to 6th decades of life.[25] The exact etiology of PRC is unknown, but is seen frequently in patients with BPH[25] and could be the result of obstruction of the prostatic parenchymal ductules.[26] On imaging, these are round, smooth unilocular cysts and can occur in any prostatic
zone, usually the peripheral zone with or without background changes of BPH ([Fig. 10A, B]). Cystic degeneration of BPH nodules results in irregularly shaped cysts commonly
seen in the TZ of the prostate gland ([Fig. 10C]).
Fig. 10 (A, B): A 62-year-old gentleman with bladder outlet obstruction symptoms. Trans-abdominal
ultrasound (A) and transrectal ultrasound (B) showing an enlarged prostate with an anechoic lesion in the left transition zone
in the midgland level (arrowhead) likely cystic degeneration of benign prostatic hyperplasia.
(C) Axial high-resolution T2 magnetic resonance imaging showing a well-defined unilocular
cyst in the right posterolateral peripheral zone(arrowhead) at mid-gland level that
was incidentally detected in a patient with left renal agenesis suggestive of a prostate
retention cyst.
Tumoral cysts
Some tumors like multilocular prostatic cystadenoma and adenocarcinoma also show cystic
changes along with soft tissue components.[24]
[28]
Periprostatic cysts include SV cysts, cyst of vas deferens, and Cowper's duct cysts.[24]
Seminal vesicle cysts
These can be congenital or acquired and may be associated with adult polycystic kidney
disease.[26]
[27] These are mostly detected incidentally unless they are large enough to cause obstructive
urinary symptoms.[29] They occur commonly in sexually active males secondary to a malformed or stenosed
duct system.[27] When congenital, they develop due to atresia of ejaculatory ducts and thereby, are
associated with bulky distended SV. Congenital cysts are mostly unilateral and associated
with anomalies like renal agenesis, ectopic ureteric insertion, and vas deferens agenesis.
Zinner syndrome is a triad of unilateral renal agenesis, ipsilateral SV cyst, and
ejaculatory duct obstruction[27] ([Fig. 11]). On imaging, they appear as well-defined round/oval/tubular cysts within the SV,
posterior to the urinary bladder.[26]
[29] In cases of hemorrhage and proteinaceous content, they appear hyperintense on T1-weighted
imaging and hypointense to bladder contents on T2 weighted imaging ([Fig. 11]).[27] On TRUS, they are seen as anechoic cystic lesions within the SV with variable echogenicity
in the presence of hemorrhage or proteinaceous content.[27]
[29] These cysts are usually treated with conservative management. However, TRUS-guided
cyst drainage can be done if symptomatic.[27]
Fig. 11 A 33-year-old gentleman with infertility. Coronal (A) high-resolution T2-weighted (T2W) image of the abdomen showing left renal agenesis
(arrowhead), and axial (B) high-resolution T2W magnetic resonance image of the pelvis showing ipsilateral seminal
vesicle cyst (arrowhead) indenting the left posterior wall of the urinary bladder,
suggestive of Zinner syndrome.
Cysts of the vas deferens
Ductus deferens, formerly called vas deferens, is a muscular tube that transports
sperm from epididymis to ejaculatory ducts. These cysts are seen along the ductus
deferens and cranial to the prostate gland and posterior to the urinary bladder.[27]
[28] On MRI, these are seen as well-defined T1 hypointense, T2 hyperintense fluid signal
thin-walled cysts and are not easily confused with other differentials[26]
[27] due to their location along the course of the ductus deferens.
Cowper's (bulbourethral) duct cysts
Cowper's glands are paired structures located on either side of the urogenital diaphragm
at the level of the membranous urethra.[30] Secretions from each gland drain into individual ducts that join to form a single
duct that empties into the proximal bulbar urethra.[31] The dilatation of the duct called syringocele is very rare and develops due to duct
obstruction. Based on its communication with the urethra, it is divided into open
type and closed type.[30] These can be congenital or acquired, and encountered more often in pediatric population.
The majority of them are asymptomatic. Symptoms if present include recurrent UTIs,
voiding problems, dysuria, and palpable perineal mass.[32] On imaging, these are seen as well-defined midline or paramedian cysts that appear
anechoic on ultrasound and hyperintense on T2-weighted MRI, located posterior to the
posterior urethra and inferior to the prostatic apex[27] ([Fig. 12]). Asymptomatic or mildly symptomatic cases are kept under surveillance and patients
with severe symptoms are managed by endoscopic deroofing of the cyst. Other options
include endoscopic/ open trans-perineal excision or ligation of the cyst[33]
Fig. 12 Incidentally detected Cowper's duct cyst in a 38-year-old gentleman with rectal bleeding.
Axial (A), coronal (B), and sagittal (C) high-resolution T2-weighted images of the prostate showing a small ovoid hyperintense
lesion at the base of the penile urethra, posterior to the posterior urethra and inferior
to the prostate apex.
Ureteroceles, dilatation of the prostatic urethra after TURP, bladder diverticula,
hydroureter and ectopic insertion of the ureter ([Fig. 13]) are mimickers of prostatic and periprostatic cysts and the differentiating features[2]
[4] have been tabulated in [Table 3].
Fig. 13 Mimics of prostatic and periprostatic cysts. (A, B) A 72-year-old with post-transurethral resection of the prostate (TURP) status. Axial
(A) and coronal (B) high-resolution T2-weighted images showing post-TURP defect (arrowhead). Axial computed
tomography (C) images of a 62-year-old gentleman showing a large urinary bladder diverticulum along
left lateral aspect of the bladder (arrowhead), which shows communication (D) with the urinary bladder(arrowhead).
Table 3
Differentiating features of various mimickers of prostatic and periprostatic cysts
|
Mimics
|
Imaging
|
Is it difficult to differentiate?
|
|
Defect from transurethral resection of prostate:
|
Funnel-shaped irregular defect in the mid part of upper end of prostate. It is seen
communicating with the urinary bladder
|
Easily identified as a defect rather than a cystic lesion in the appropriate clinical
setting
|
|
Hydroureter and ectopic insertion of ureter:
|
Hydroureter with tortuous course can look like a periprostatic lesion.
Ectopic insertion of the ureter into the prostatic part of the urethra can also mimic
a periprostatic cyst
|
Evaluation in multiple planes is helpful in the diagnosis
|
|
Urinary bladder diverticulum:
|
These mimic periprostatic cysts when located along the prostate or seminal vesicle
|
Communication of these cysts with the urinary bladder confirms the diagnosis
|
Benign Neoplasms of Prostate and Seminal Vesicles
Benign Neoplasms of Prostate and Seminal Vesicles
A wide variety of neoplasms, both benign and malignant can occur in the prostate and
SV.[34] Malignant neoplasms are much more common than benign neoplasms, with acinar adenocarcinoma
being the most common neoplasm. Benign neoplasms are of mesenchymal origin and constitute
less than 1% of all tumors.[35] They generally are large lesions that cause nonspecific and chronic lower urinary
tract symptoms. PSA levels will usually be normal in these neoplasms because PSA is
produced by epithelial cells of the prostate, which enter the bloodstream when the
blood epithelial barrier is destroyed.
Stromal Tumors of Uncertain Malignant Potential
Prostatic stromal tumors of uncertain malignant potential (STUMPs) are rare stromal
tumors with unpredictable biological behavior. They are reported to occur in adults
of any age, with the highest prevalence in the 6th to 7th decades.[34] Based on the histologic appearance, there are five patterns of STUMPs.[34] The most common pattern is a lesion with hypercellular stroma with scattered atypical
but degenerative-looking cells admixed with benign prostatic glands. A distinctive
pattern of STUMP is the phyllodes subtype, with a leaf-like growth pattern. Stromal
tumors are positive for CD34 and progesterone receptors and uncommonly express estrogen
receptors.
STUMPs commonly arise from the peripheral zone rather than the TZ of the gland and
appear as a solitary, sharply circumscribed, solid or solid-cystic mass with solid
areas showing T1 hypointense and T2 hyperintense signal ([Fig. 14]) on MRI.[36] The cystic component can be clear fluid, mucinous, or blood. A rim-like hypointense
“capsule” is characteristically seen on T2-weighted images ([Fig. 14]). The solid components of the lesion show gradual enhancement on DCE-MRI. Large
tumors may invade adjacent organs such as the rectum and there are case reports of
metastases to the lungs and bones.[37] The differential diagnosis includes BPH nodules, cystadenoma ([Fig. 18]), sarcomas, and other mesenchymal lesions. Treatment of STUMP is complete surgical
resection; however, they frequently recur (up to 65%).[37]
Fig. 14 Stromal tumor of uncertain malignant potential (STUMP) in a 66-year-old male. T2
image in axial (A), sagittal (B), and coronal (C) planes showing a well-circumscribed solid-cystic lesion arising from the posterior
peripheral zone of the prostate gland with a rim-like T2 hypo-intense “capsule” (arrowhead
in B and C). The T1 image in the axial plane (D) showing that the cystic areas are T1 hyperintense suggesting blood products (arrow
in D). Apparent diffusion coefficient map (E) showing no diffusion restriction. Histopathology microphotograph (F) confirms the diagnosis of STUMP showing complex branching glands and increased stromal
cellularity (hematoxylin and eosin x 40).
Fig. 15 A 44-year-old male with a palpable paraumbilical mass on clinical examination. (A–C) Oblique sagittal, oblique coronal, and axial computed tomographic images of a well-marginated,
and pedunculated solid lesion arising from the left seminal vesicle showing heterogeneous
enhancement with no invasion to adjacent structures. (D) High-resolution T2 axial images showed that the lesion is predominantly T2 hypointense.
(E) Histopathology confirmed the diagnosis of leiomyoma of the seminal vesicle with
fascicles of spindle cells with eosinophilic cytoplasm, blunt-ended oval nuclei, and
minimal to no cytological atypia (hematoxylin and eosin x 100).
Fig. 16 A 53-year-old male with acute painless urinary retention and an enlarged firm nontender
prostate gland, on clinical examination. Prostate-specific antigen was 0.88 IU/mL.
Multiparametric magnetic resonance imaging of the prostate. T2-weighted images in
axial (A) and coronal (B) planes showed a well-defined lesion from the prostate with heterogeneously hypointense
signal intensity. Diffusion-weighted imaging with b 1500 (C) and apparent diffusion coefficient (D) images showed areas of restricted diffusion. Delayed postcontrast subtraction image
(E) reveals gradual enhancement. Histopathology microphotograph (F) diagnosed it to be a solitary fibrous tumor with variable cellularity, and dense
hyalinized collagenous stroma (hematoxylin and eosin x 200). The tumor cells stained
positive for STAT6 (Inset image in F).
Fig. 17 Ectopic prostate tissue in a patient who presented with right flank pain. T2 axial
image showing concentric thickening (arrowhead) of the right terminal ureter. This
was diagnosed to be prostate parenchyma on cystoscopy and biopsy. (This case was contributed by Prof. Mukesh Harisinghani, MGH, USA).
Fig. 18 Prostate cystadenoma in a 40-year-old male. T2 image in axial (A) and sagittal (B) planes showing a well-encapsulated multiloculated cystic lesion (arrowheads in A
and B) in the transition zone of the prostate with no solid areas. A small prostatic
utricle cyst is seen in the posterior peripheral zone in the midline (arrow in A).
Benign Nonstromal Mesenchymal Tumors
Benign non-stromal mesenchymal tumors arise from smooth muscle elements in prostatic
stroma or peri glandular tissue. Leiomyoma, schwannoma, solitary fibrous tumor (SFT),
inflammatory myofibroblastic tumor (IMT), and paragangliomas are benign mesenchymal
tumors reported to arise from prostate and are very rare.[36] Generally, they have non-specific imaging features and need a biopsy for a definitive
diagnosis. The differentiation between benign and malignant mesenchymal tumors also
may be difficult unless there is definite evidence of local invasion or metastasis.
Leiomyoma arising within the gland can resemble the stromal nodule of BPH if it is
small, though most of them are very large at presentation.[38] Imaging shows a well-defined, solitary, solid mass with predominantly homogeneous
enhancement. At MRI, T1 and T2-weighted images have low signal intensity and homogeneous
enhancement when small, but large lesion can be heterogeneous on T2 and postcontrast
images due to necrosis ([Fig. 15]). Expression of smooth muscle actin and desmin confirms the diagnosis, while CD34
is negative, distinguishing it from STUMP.[39]
Schwannomas typically arising in the 4th to 6th decades are commonly sporadic. A smaller proportion can be associated with
hereditary syndromes like neurofibromatosis type 2 and schwannomatosis.[40] On CT, sporadic schwannomas are typically well-circumscribed solitary oval masses
with cystic changes, calcifications, and variable enhancement. MRI usually shows low
T1 signal intensity, heterogeneous high T2 signal, and variable post contrast enhancement.[41]
[42]
SFT originating from prostate is rare and have been reported previously among different
age group ranging from 21 to 75 years. They are generally large lesions over 5 cm
and may induce paraneoplastic syndromes like hypoglycemia (Doege-Potter syndrome)
due to tumor-secreted insulin-like growth factor-2.[43]
[44] On MRI, SFT appears hypointense on T1-weighted images and displays mixed heterogeneous
signal intensity on T2-weighted images, dependent on collagen or other components.
Gradual post enhancement is seen owing to fibrous content. Diffusion restriction may
indicate areas of high cellularity ([Fig. 16]).[45] Surgical removal remains the primary treatment; however, recurrence is reported
in 10 to 30% of cases.[46]
Prostate IMT has been reported between ages 21 to 83 years.[38]
[47] They appear hypointense on T1-weighted images and mixed heterogeneous on T2-weighted
images depending on fibrosis and inflammation. Contrast-enhanced CT and MRI can display
avid, homogeneous, or heterogeneous enhancement.[36]
Prostate paragangliomas are rare tumors derived from extra-adrenal chromaffin cells
in sympathetic or parasympathetic paraganglia. They can have sporadic or familial
occurrences (linked to syndromes like MEN 2A/B, von Hippel-Lindau, neurofibromatosis
type 1, Carney complex, and familial paraganglioma syndromes). Functioning types may
exhibit catecholamine-related symptoms.[48]
[49] In contrast to CT and MRI, paraganglioma appears as hyper enhancing lesion reflecting
the richly vascularized nature of these tumors. At MRI, paragangliomas typically show
marked T2 hyperintensity with classic salt-and-pepper appearance due to multifocal
signal voids. They tend to have high signal intensity at high b-value DWI, but the
signal on the ADC map is not reduced or only mildly reduced. PET imaging with 68Ga
DOTATATE will show marked avidity.[49]
Ectopic Prostate Tissue
Ectopic prostatic tissue (EPT) is defined as the presence of prostatic tissue at sites
other than the prostate. It is mostly reported in the urethra and bladder and less
commonly reported in the genital tract involving SV, epididymis, and testis.[50]
[51] There are case reports of EPT described in other locations, including the bowel,[52] pelvis,[53]
[54] and spleen.[55] The origin of this around the lower urinary tract is believed to be vestigial remnants
of developmental migration, while other sites may involve metaplasia or misplacement
of prostate glands during development.[51] Clinical manifestations of EPT in the lower urinary tract include hematuria or urinary
obstruction. EPT in the rest of the sites is either asymptomatic or has non-specific
symptoms.[51] Prostate hyperplasia and neoplasms developing in EPT have been reported.[51]
[52] MRI shows the typical signal intensity of the prostate gland with or without hyperplasia
and [Fig. 17] is an example of EPT in the right distal ureter. The symptomatic patients are managed
surgically.
Cystadenoma of the Prostate and Seminal Vesicle
Cystadenoma of the prostate and SV are rare benign multi-locular cystic tumors. Though
the same nomenclature is used for both prostate and SV lesions, they are classified
separately in the World Health Organization classification with some differences in
pathology.[34] These lesions are reported in patients between 16 and 80 years and are usually large
lesions measuring over 7 cm.[36] They cause obstructive and irritative urinary symptoms due to their large size.
The serum PSA level is often elevated in prostate cystadenoma while always normal
in SV cystadenoma. Histological examination shows cysts lined by cuboidal cells without
atypia in the background hypocellular stroma.[34] Immunohistochemical staining will be positive for PSA and prostate-specific acid
phosphatase in prostate cystadenoma while they are negative in SV cystadenoma. Imaging
helps in determining the epicenter of lesion (prostate or SV). Apart from the difference
in the epicenter of the lesion, the imaging characteristics of both prostatic and
SV cystadenomas are similar and are seen as large well-encapsulated multi-locular
cystic masses that may have minimal solid areas ([Figs. 18] and [19]).[56] The cyst contents can range from simple fluid, to non-simple hemorrhagic or proteinaceous
fluid, and imaging can show fluid-fluid levels. Enhancement of the septa and solid
components may be observed. Surgical resection of the lesion is curative.
Fig. 19 Seminal vesicle cystadenoma in a 57-year-old male. T2 images in the axial (A) and sagittal (B) planes and T1 images in the axial (C) plane showing a large encapsulated multiloculated cystic mass with no solid areas
from the left seminal vesicle. The prostate is seen separately (arrowhead). The loculi
of the tumor showing varying T1 and T2 signal intensities (arrows). Histopathology
microphotograph (D) confirms the diagnosis and shows cyst wall and papillary structures lined by a single
layer of cells (hematoxylin and eosin x 40).
Conclusion
Imaging diagnosis and differential diagnostic considerations for Non-malignant prostatic
and SV lesions are broad. Along with the imaging findings, we must consider the clinical
context, past medical history, treatment history, current symptoms, age of the patient,
clinical examination findings, and serum PSA level to provide an accurate diagnosis
and logical differential diagnosis. Knowledge of these conditions can help us identify
or suspect entities that may mimic clinically significant prostate cancer on mpMRI
in the appropriate clinical setting.
