Modern radiology offers several ways to visualize the internal structures of the penis, and which tool a clinician reaches for depends almost entirely on the clinical question being asked. MRI provides the highest soft-tissue contrast and is considered the gold standard for staging penile cancer, while Doppler ultrasound is the workhorse for evaluating blood flow during erection and diagnosing erectile dysfunction. Retrograde urethrography remains the go-to for mapping urethral strictures, and CT earns its place in emergencies like necrotizing infections and prosthesis complications. Understanding what each modality reveals, and where each falls short, matters for anyone navigating a diagnosis involving penile pathology.
How MRI Reveals Normal Penile Anatomy
MRI excels at showing the soft-tissue layers of the penis because of its superior contrast resolution. The paired corpora cavernosa (the two cylindrical chambers responsible for erection), the corpus spongiosum (the ventral chamber surrounding the urethra), the tunica albuginea (the tough fibrous sheath encasing each chamber), and the surrounding fascial planes can all be distinguished on high-resolution sequences. T2-weighted imaging is particularly useful because fluid-rich tissues appear bright, making the internal architecture stand out clearly. When the penis is imaged during pharmacologically induced tumescence, using an injected agent like alprostadil, the corpora fill with blood and the tunica albuginea becomes even more distinct. This combination of tumescence and high-resolution T2 sequences shows the glans, corpora, and tunica albuginea well.1PubMed Central. MRI of the penis
In practical terms, MRI is not the first imaging test ordered for most penile complaints. It is slower, more expensive, and less widely available than ultrasound. But when the question involves tumor extent, deep tissue involvement, or complex anatomy that ultrasound cannot fully resolve, MRI is the modality that gives surgeons the clearest map of what they are dealing with.
Doppler Ultrasound and the Erection Cycle
Penile Doppler ultrasound is the most commonly used imaging study for evaluating erectile dysfunction. It is noninvasive (or minimally invasive, since a vasoactive agent is typically injected into the corpora cavernosa to trigger an erection), it works in real time, and it gives detailed information about blood flow that no other modality matches at this cost and accessibility level.2PubMed Central. Penile Doppler ultrasonography revisited With the help of intracavernosal injections such as alprostadil, clinicians can produce a detailed picture of the hemodynamics throughout the erection cycle.3PubMed. A Review on Penile Doppler and Ultrasonography for Erectile Dysfunction
The test measures two key velocities. Peak systolic velocity (PSV) reflects how much arterial blood flows into the corpora during erection. End-diastolic velocity (EDV) reflects how well the venous outflow shuts down to trap blood and maintain rigidity. A PSV above 30 cm/sec is generally considered normal, while an EDV below 5 cm/sec suggests that the veno-occlusive mechanism is working properly.4PubMed Central. EFFICIENT USE OF PENILE DOPPLER ULTRASOUND FOR INVESTIGATING MEN WITH ERECTILE DYSFUNCTION The accuracy of the entire test depends on achieving complete smooth muscle relaxation in the corpora. If the smooth muscle does not fully relax, blood flow measurements will be artificially low, potentially leading to a false diagnosis. A redosing protocol, where additional vasoactive agent is administered if the first dose does not produce full rigidity, helps avoid this pitfall.
Sorting Out the Vascular Causes of Erectile Dysfunction
Doppler ultrasound can broadly separate erectile dysfunction into arterial and venous subtypes, and this distinction drives treatment decisions. Arteriogenic ED is diagnosed when arterial inflow is insufficient. PSV values below 25 cm/sec are considered clearly abnormal, values above 35 cm/sec are normal, and the range between 25 and 35 cm/sec is equivocal.5PubMed Central. Diagnostic categorization of erectile dysfunction using duplex color doppler ultrasonography and significance of phentolamine redosing in abolishing false diagnosis of venous leak impotence Men in that gray zone may need repeat testing or additional evaluation.
Venogenic ED, sometimes called venous leak, occurs when arterial inflow is adequate but the veins fail to compress enough to trap blood. On Doppler, this shows up as a PSV above 30 cm/sec (proving the arteries deliver enough blood) combined with a persistently elevated EDV above 5 cm/sec and a low resistive index below 0.9.5PubMed Central. Diagnostic categorization of erectile dysfunction using duplex color doppler ultrasonography and significance of phentolamine redosing in abolishing false diagnosis of venous leak impotence One important limitation is that EDV becomes unreliable when arterial inflow is already poor, because low inflow can mask a coexisting venous leak.
Duplex ultrasonography has strong predictive value for venous leak when performed carefully. In one study, the positive and negative predictive values for detecting corporal venous leakage were 90% and 100%, respectively, confirmed against cavernosography.6Journal of Vascular Surgery. Diagnostic value of duplex ultrasonography in vasculogenic impotence For cases where Doppler results are inconclusive and the clinical suspicion of venous leak is high, CT cavernosography with three-dimensional volume rendering can provide a detailed look at the venous drainage pathways, particularly in younger patients.7British Journal of Radiology. Computed tomography cavernosography combined with volume rendering to observe venous leakage in young patients with erectile dysfunction
Imaging Penile Fracture
A penile fracture is a rupture of the tunica albuginea, usually occurring during vigorous sexual activity. It is a clinical emergency, and while the diagnosis is often made on physical examination alone (a sudden “pop,” rapid detumescence, and eggplant-like swelling are classic signs), imaging plays an important role in surgical planning. The surgeon needs to know exactly where the tear is and whether the urethra is involved.
MRI is the more accurate tool for this job. In a head-to-head comparison, MRI detected the fracture in all patients (100% detection rate) and mapped the tear location precisely in 97% of cases. Ultrasound detected 88% of fractures and mapped them correctly in 81%.8PubMed. The role of ultrasound (US) and magnetic resonance imaging (MRI) in penile fracture mapping for modified surgical repair A larger pooled analysis reported MRI sensitivity and specificity of about 92% and 91%, respectively, compared with roughly 71% sensitivity and 100% specificity for ultrasound.9PubMed Central. Diagnostic performance of MRI and US in suspicion of penile fracture Ultrasound had perfect specificity in that analysis, meaning it rarely calls something a fracture when it isn’t, but its lower sensitivity means it misses some tears. MRI also detected urethral injury more frequently, picking it up in about 16% of cases compared with about 10% for ultrasound.
In practice, many hospitals use ultrasound first because it is fast and available around the clock. MRI is reserved for cases where ultrasound findings are inconclusive or when the surgeon specifically needs to rule out urethral involvement before taking the patient to the operating room.
Priapism and the Role of Color Doppler
Priapism, a prolonged erection unrelated to sexual arousal, comes in two forms that require very different treatment, and imaging is often the fastest way to tell them apart. Ischemic (low-flow) priapism is an emergency in which blood is trapped in the corpora without adequate circulation, while non-ischemic (high-flow) priapism results from unregulated arterial inflow, usually after trauma that creates an abnormal connection between an artery and the cavernosal tissue.
Color Doppler ultrasound is the primary imaging modality for this distinction. It can assess the hemodynamics of the cavernosal arteries in real time, confirming whether flow is absent or sluggish (ischemic) versus brisk and turbulent (non-ischemic). In non-ischemic cases, it can also pinpoint the location of an arteriovenous fistula.10International Journal of Impotence Research. Review of the role of imaging in the diagnosis of priapism Blood gas analysis of aspirated cavernosal blood adds biochemical confirmation, and internal pudendal arteriography has also proven useful.11PubMed. Diagnosis and treatment of priapism: experience with 5 cases For high-flow priapism caused by a traumatic fistula, superselective transcatheter embolization, performed under angiographic guidance, has been used successfully to occlude the abnormal vessel and resolve the condition.12PubMed. “High-flow” priapism: treatment with superselective transcatheter embolization
Peyronie’s Disease on Ultrasound
Peyronie’s disease involves the formation of fibrous plaques within the tunica albuginea, leading to penile curvature and sometimes pain during erection. Ultrasound is the first-line imaging modality because it can identify, measure, and characterize these plaques, including those too small to feel on physical examination.13PubMed Central. US Imaging in Peyronie’s Disease Detection of calcification within a plaque suggests that the disease has stabilized, which helps clinicians decide whether to pursue medical therapy, injections, or surgery.
Plaques can take several forms. In a study of patients who had Peyronie’s disease without palpable plaques, ultrasound identified three distinct patterns: focal calcified thickening of the septum between the corpora (accounting for roughly 78% of cases), non-calcified thickening (about 15%), and scattered microcalcifications without a solid plaque (about 7%). Plaque sizes ranged from 3 to 13 mm.14PubMed Central. Sonographic patterns of Peyronie’s disease in patients with absence of palpable plaques The ability to find and characterize these lesions even when they cannot be felt gives ultrasound a clear advantage over physical examination alone and helps guide treatment selection.
Staging Penile Cancer
Penile cancer is rare, but accurate staging determines whether a patient can undergo organ-sparing surgery or requires more radical treatment. The critical questions are how deeply the tumor invades the local tissues and whether lymph nodes are involved. MRI is considered the gold standard for answering both.15PubMed Central. Comprehensive review of penile cancer using MR imaging On T2-weighted sequences, tumor tissue typically appears different in signal intensity from the surrounding normal anatomy, allowing radiologists to assess whether cancer has breached the tunica albuginea, invaded the corpora cavernosa, or extended into the urethra. Gadolinium-enhanced sequences add further detail by highlighting areas of abnormal blood supply within the tumor.
Because the depth of invasion directly affects whether the glans can be preserved, the precision of MRI can make a real difference in quality of life after treatment. Ultrasound and CT are sometimes used as adjuncts, but neither matches MRI’s soft-tissue resolution for the primary tumor.
Urethral Stricture Imaging
A urethral stricture is a narrowing of the urethra caused by scar tissue, and the imaging workup focuses on mapping the stricture’s location, length, number of narrowed segments, and severity. The gold standard remains retrograde urethrography (RUG), a fluoroscopic study in which contrast is injected into the urethra and X-ray images are captured as the dye fills the channel. For complex cases involving the posterior urethra, RUG can be combined with a voiding cystourethrogram (VCUG) for more complete visualization.16PubMed Central. Imaging of urethral stricture disease Determining the number, length, severity, and location of strictures is essential for choosing between endoscopic treatment, open repair, or staged reconstruction.17PubMed. Anterior urethral strictures and retrograde urethrography: An update for radiologists
RUG has one well-known limitation: it shows the lumen of the urethra but not the tissue surrounding it. Sonourethrography (SUG), in which saline or gel is instilled into the urethra while an ultrasound probe is placed along the penile shaft, adds information about the depth of scarring (spongiofibrosis) in the surrounding corpus spongiosum. In comparative studies, sonourethrography detected spongiofibrosis with sensitivities in the range of 77% to 83%.18PubMed. A comparison of sonourethrography and retrograde urethrography in evaluation of anterior urethral strictures Interestingly, strictures measured by SUG tend to appear shorter than those measured by RUG. In one study the mean length measured by RUG was about 13 mm versus about 8 mm by SUG, a statistically significant difference.19PubMed Central. Comparison of Diagnostic Value of Sonourethrography with Retrograde Urethrography in Diagnosis of Anterior Urethral Stricture This discrepancy probably arises because RUG can overestimate length when contrast fails to distend the urethra fully upstream of a tight narrowing.
Sonoelastography, a newer technique that measures tissue stiffness, has shown promising accuracy for mapping both stricture extent and depth of spongiofibrosis. In one comparison, sonoelastography achieved an overall diagnostic accuracy for stricture location and length of about 93%, compared with roughly 79% for standard sonourethrography and about 80% for RUG. For estimating the depth of scarring, sonoelastography reached about 87% accuracy versus 48% for conventional sonourethrography.20PubMed Central. Comparison of sonoelastography with sonourethrography and retrograde urethrography in the evaluation of male anterior urethral strictures MRI urethrography is considered the most accurate method overall and is especially valuable for post-traumatic or posterior urethral strictures, though it remains less widely available.21PubMed Central. Retrograde urethrography, sonouretrography and magnetic resonance urethrography in evaluation of male urethral strictures
Fournier Gangrene and Infectious Emergencies
Fournier gangrene is a rapidly spreading necrotizing infection of the perineal and genital soft tissues that carries significant mortality. Imaging is critical both for confirming the diagnosis and for mapping the extent of tissue destruction before surgical debridement. CT is the primary modality here. It demonstrates asymmetric fascial thickening, fluid collections, abscess formation, fat stranding, and the hallmark finding: subcutaneous emphysema caused by gas-forming bacteria.22PubMed. Fournier gangrene: role of imaging CT can also reveal the underlying source of infection, such as a perianal abscess or fistula, which helps guide both surgical and medical management.23PubMed Central. A case report of Fournier’s gangrene: Imaging ultrasound and computed tomography (CT) scan
Ultrasound can contribute in the scrotal component of the disease. It typically shows thickened, swollen scrotal walls with increased blood flow on Doppler, and it may detect subcutaneous gas as bright echogenic foci with dirty acoustic shadowing, sometimes before the gas is clinically apparent as crepitus on physical exam. The testes and epididymides usually look normal, which helps distinguish Fournier gangrene from primary testicular pathology.23PubMed Central. A case report of Fournier’s gangrene: Imaging ultrasound and computed tomography (CT) scan Abscesses and pyoceles can also be identified on ultrasound.24PubMed. Imaging of penile and scrotal emergencies The speed and bedside availability of ultrasound make it useful for initial triage, but CT remains the definitive study for surgical planning.
Penile Prosthesis Complications
Inflatable penile prostheses are the most durable treatment for medically refractory erectile dysfunction, but they carry their own set of mechanical and infectious complications. Imaging is essential when something goes wrong, and no single modality covers every scenario. Complications fall into three broad categories: malpositioning (buckling, floppy glans, erosion, migration, cylinder crossover), mechanical failure (fracture, aneurysm, leakage), and infection. Among the imaging options, MRI is considered the most useful overall for evaluating these problems.25PubMed. Comprehensive Multimodality Imaging Review of Complications of Penile Prostheses
CT, while not always the first choice for soft-tissue penile imaging, earns a clear role in prosthesis evaluation. It is fast, inexpensive relative to MRI, and immediately available in emergent situations like infection, hematoma, or component erosion. CT is very sensitive for detecting fluid leaks from the prosthesis and can identify cylinder complications, pump malposition, and issues useful for preoperative planning if revision surgery is needed.26PubMed. CT imaging of inflatable penile prosthesis complications: a pictorial essay MRI adds value by showing the relationship between the device and the surrounding soft tissues in finer detail, which is particularly helpful for subtle erosion, cylinder crossover, or floppy glans syndrome.27PubMed. Magnetic resonance imaging of penile Prostheses: A pictorial review of normal appearances and complications
Imaging After Gender-Affirming Surgery
Genital reconstruction in transgender men typically involves phalloplasty or metoidioplasty, often accompanied by scrotoplasty and sometimes erectile device implantation. Imaging is needed postoperatively primarily to check on the neourethra, the surgically constructed urinary channel. Urethrography is the standard modality used to evaluate neourethral patency and to detect complications such as leaks and fistulas.25PubMed. Comprehensive Multimodality Imaging Review of Complications of Penile Prostheses Radiologists who encounter post-phalloplasty imaging need familiarity with the surgically altered anatomy to avoid misinterpreting normal postoperative findings as pathology.
Congenital Anomalies in Pediatric Imaging
MRI is increasingly used to map the anatomy of the penis in children with congenital anomalies, particularly hypospadias, a condition in which the urethral opening is located on the underside of the penis rather than at the tip. In a study of 24 children with hypospadias, MRI visualized the penile soft tissues and fascial planes clearly. The most common subtype was subcoronal hypospadias, accounting for about 58% of cases, followed by midpenile (roughly 21%) and distal penile (about 13%). The mean urethral plate thickness was approximately 1.3 mm.28PubMed. Anatomical study of hypospadias penis using magnetic resonance imaging in children These measurements help surgeons plan repair by predicting whether the native urethral plate is thick enough to support reconstruction, potentially reducing the need for more complex procedures.
Operator Dependence and Common Pitfalls
One theme that runs through nearly every penile imaging modality is how much the quality of the result depends on the person performing or interpreting the study. Doppler ultrasound is especially vulnerable to this. Variability in imaging protocols, improper Doppler settings, and operator dependency can lead to artifacts or misinterpretations.29British Journal of Radiology. Unveiling gaps in MRI for penile Mondor’s disease: a systematic review In erectile dysfunction evaluation, the biggest source of false results is inadequate smooth muscle relaxation. If the patient is anxious and the corpora do not fully relax, blood flow measurements will underestimate true arterial inflow, potentially labeling a man as having arteriogenic ED when his arteries are actually fine. The redosing protocols described earlier exist precisely to guard against this, but not every clinic follows them rigorously.4PubMed Central. EFFICIENT USE OF PENILE DOPPLER ULTRASOUND FOR INVESTIGATING MEN WITH ERECTILE DYSFUNCTION
MRI avoids some of these operator-dependent issues because the images are acquired in a standardized way and interpreted afterward, but it introduces its own challenges. Motion artifact from patient movement, suboptimal coil placement, and the difficulty of achieving consistent tumescence during a scan can all degrade image quality. For urethral imaging, RUG depends on proper contrast injection technique; too little pressure may fail to distend a stricture, making it look longer or tighter than it actually is, which is likely why RUG tends to overestimate stricture length compared with ultrasound-based methods. In every case, the quality of penile imaging is only as good as the protocol followed and the expertise of the person at the controls.