Penile Anatomy Radiology: A Detailed Imaging Overview

Medical imaging plays a crucial role in evaluating penile anatomy, aiding in the diagnosis of vascular conditions, trauma, fibrosis, and congenital anomalies. Accurate interpretation requires an understanding of normal structures and their appearance across different modalities.

This article provides an overview of how imaging techniques visualize penile anatomy, focusing on key structural and vascular features.

Penile Layers Shown On Imaging

Medical imaging allows detailed visualization of the penis’s structural layers, each essential for function and integrity. High-resolution ultrasound, MRI, and CT scans provide distinct views, aiding in diagnosing traumatic injuries, fibrotic changes, and congenital differences.

Skin And Fascia

The outermost penile layers, including skin and fascia, are best visualized with high-frequency ultrasound due to its superior resolution. The skin appears as a thin, hyperechoic layer, while the underlying superficial fascia (Colles’ fascia) and deep fascia (Buck’s fascia) differ in echogenicity. MRI enhances structural delineation, with T1-weighted sequences highlighting subcutaneous fat and T2-weighted images enhancing soft tissue contrast.

Imaging of these layers is crucial for detecting conditions like Peyronie’s disease, where Buck’s fascia may exhibit fibrotic thickening, and penile lymphedema, which presents as diffuse skin thickening. In trauma cases, disruption of these layers can indicate penile degloving injuries requiring surgical intervention. A Journal of Urology (2022) study emphasized MRI’s role in distinguishing inflammatory from neoplastic skin lesions, aiding early diagnosis.

Tunica Albuginea

The tunica albuginea, a dense fibrous layer surrounding the corpora cavernosa, is critical for penile rigidity. On ultrasound, it appears as a hyperechoic line encasing the erectile tissues. Dynamic sonography with manual compression can reveal disruptions or hematomas indicative of rupture. MRI, particularly T2-weighted imaging, provides additional detail, showing discontinuity or fluid collection at fracture sites.

A European Radiology (2021) analysis found MRI had a 95% sensitivity in detecting tunical tears, making it the preferred modality for complex cases. Imaging also plays a key role in Peyronie’s disease, where calcifications, best seen on CT, and fibrotic plaques, visible as hypointense areas on MRI, guide treatment decisions, including surgical plaque excision or collagenase injection therapy.

Corporal Bodies

The corpora cavernosa and corpus spongiosum form the main erectile structures, with distinct imaging characteristics. Ultrasound with Doppler evaluation assesses vascular function, while grayscale imaging reveals internal architecture. The corpora cavernosa appear as paired, homogenous structures with intermediate echogenicity, while the corpus spongiosum is slightly more hypoechoic due to its higher vascularity.

MRI provides superior soft tissue contrast, with T1-weighted images demonstrating uniform signal intensity and T2-weighted sequences highlighting internal trabecular structures. Conditions like corporal fibrosis, seen in post-priapism states, appear as hypointense regions on both modalities. In suspected malignancy cases, MRI with contrast enhancement helps distinguish benign from malignant lesions. A Radiology (2023) study highlighted diffusion-weighted imaging’s role in identifying early-stage penile tumors.

Vessels And Blood Flow

Imaging is essential for evaluating penile vascular structures, crucial for erectile function and overall health. Doppler ultrasound is the primary modality for assessing arterial inflow and venous drainage, while MRI with contrast provides additional vascular detail.

Dorsal Arteries

The dorsal arteries, running along the penis’s dorsal aspect, supply blood to the skin, fascia, and glans. On Doppler ultrasound, they appear as paired, pulsatile structures with a triphasic waveform in healthy individuals. Peak systolic velocity (PSV) measurements assess arterial sufficiency, with values above 25 cm/s considered normal.

A Journal of Sexual Medicine (2021) study found reduced PSV in the dorsal arteries correlated with arteriogenic erectile dysfunction. MRI angiography further delineates arterial anatomy and detects stenosis or occlusion. In penile trauma, imaging may reveal thrombosis or disruption of these vessels, which can contribute to ischemic complications. High-resolution ultrasound can also identify Mondor’s disease, a superficial thrombophlebitis of the dorsal vein that may extend to the arteries.

Cavernosal Arteries

The cavernosal arteries, located within the corpora cavernosa, are the primary blood supply for erectile function. Color Doppler ultrasound, particularly during pharmacologically induced erection testing, provides the best visualization. Normal cavernosal artery PSV exceeds 30 cm/s, with lower values suggesting arterial insufficiency.

A European Urology (2022) study found patients with PSV below 25 cm/s had a significantly higher prevalence of vasculogenic erectile dysfunction. Spectral Doppler analysis assesses end-diastolic velocity (EDV), with persistently elevated EDV (>5 cm/s) indicating venous leakage. MRI with contrast enhances arterial integrity assessment, particularly in post-traumatic arteriovenous fistulas, which appear as early venous filling on dynamic imaging. In Peyronie’s disease, Doppler ultrasound may reveal altered cavernosal artery flow due to plaque-induced vascular compression.

Venous Return

Penile venous drainage occurs primarily through the deep dorsal vein and emissary veins, essential for maintaining erectile function. On Doppler ultrasound, normal venous return is characterized by low-velocity, non-pulsatile flow. In venogenic erectile dysfunction, abnormal venous leakage presents as persistent diastolic flow in the deep dorsal vein, often exceeding 5 cm/s.

A systematic review in Andrology (2023) highlighted dynamic infusion cavernosometry and cavernosography (DICC) for confirming venous leak, though Doppler ultrasound remains the first-line modality. MRI with contrast further delineates venous anatomy, particularly in post-traumatic venous thrombosis or congenital venous malformations. In Peyronie’s disease, venous outflow abnormalities may result from fibrotic changes affecting the tunica albuginea.

Ultrasound Techniques

Ultrasound is the first-line imaging modality for penile evaluation due to its high resolution, real-time capabilities, and accessibility. Effective imaging depends on proper transducer selection, patient positioning, and adjunctive methods. A high-frequency linear transducer (7.5–15 MHz) is preferred for capturing fine structural details.

The penis is positioned in slight tension, either manually or resting on the lower abdomen, with generous ultrasound gel application to enhance acoustic coupling. Gray-scale ultrasound assesses structural integrity, detecting fibrosis, plaques, or trauma. Color and spectral Doppler ultrasound evaluate arterial inflow and venous competence, often performed in a flaccid state or with pharmacologically induced erection for comprehensive vascular assessment.

Tissue elasticity imaging, such as strain elastography, helps assess penile fibrosis, distinguishing pliable from fibrotic regions. Studies show elastography enhances diagnostic accuracy by quantifying plaque hardness, correlating with disease severity. Contrast-enhanced ultrasound (CEUS) improves vascular visualization by highlighting perfusion dynamics, useful in detecting subtle vascular abnormalities.

MRI Scanning Protocols

MRI offers superior soft tissue contrast for penile anatomy evaluation, aiding in structural, vascular, and pathological assessments. The optimal protocol includes supine positioning with the penis placed along the lower abdomen to minimize motion artifacts. A surface coil enhances signal reception, and an external compression device stabilizes the organ.

T1- and T2-weighted sequences provide comprehensive tissue characterization. T1-weighted imaging delineates anatomical boundaries, useful for identifying hemorrhagic or fat-containing lesions. T2-weighted sequences, particularly with fat suppression, enhance soft tissue contrast, aiding in detecting fibrosis, edema, and inflammation. Diffusion-weighted imaging (DWI) differentiates benign from malignant lesions, as malignant tissues exhibit restricted diffusion. Contrast-enhanced MRI with gadolinium highlights vascular integrity and perfusion dynamics.

CT Views Of The Penile Anatomy

CT is not the first-line modality for penile evaluation but is valuable in assessing fractures, calcifications, and vascular injuries. Its rapid cross-sectional imaging with high spatial resolution is particularly useful in trauma cases. Non-contrast CT effectively detects calcified plaques in Peyronie’s disease, appearing as hyperdense foci along the tunica.

In suspected penile fractures, contrast-enhanced CT evaluates hematomas and vascular compromise. CT angiography is useful for identifying arterial injuries such as cavernosal artery rupture or post-traumatic arteriovenous fistulas, providing critical information for embolization planning. While MRI is preferred for soft tissue assessment, CT serves as an adjunct in urgent cases.

Variations In Normal Anatomy

Penile anatomy exhibits normal variations influencing imaging interpretation. These differences, congenital or acquired, affect vascular structures, corporal symmetry, and tissue composition. Recognizing these variations prevents misdiagnosis and unnecessary interventions.

Vascular anomalies, such as accessory cavernosal arteries or dorsal vein duplication, may appear on Doppler ultrasound or MRI angiography without clinical significance. Asymmetry in corpora cavernosa size or echotexture is common. MRI also reveals tunica albuginea thickness variations, sometimes mistaken for Peyronie’s disease plaques. Understanding these differences ensures accurate interpretation.