Fig. 47.1
Hyperechoic lesion(s) with posterior acoustic shadowing
Fig. 47.2
Hyperechoic lesion of septum
These two presentations account for the majority of PD cases. Some patients however demonstrate less common findings that are often difficult to interpret.
US examination approaches 100 % sensitivity in detecting and measuring calcified plaques.
Hypoechoic/isoechoic lesions
Plaques occasionally present as hypo-/isoechoic lesions with focal thickening around the corpora cavernosa [8]. Such lesions are typical of early disease, which is characterized by mild fibrosis, strong interstitial oedema [5] and retraction of the tunica albuginea at the level of the lesion, all of which result in penile curvature. In patients receiving stimulation with prostaglandin E1 (PGE1), US imaging depicts the actual extent of the lesion, which is often difficult to assess in the flaccid penis, and can sometimes document hyperechoic lesions that are detectable only under pharmacostimulation.
Focal defects of the tunica albuginea
Focal defects of the tunica associated with a thickened posterior area are found infrequently, except in large series. The surrounding tunica may not be thickened, but it may have an abnormal undulating appearance (Fig. 47.3).
Fig. 47.3
Focal defect of the tunica albuginea
“Hourglass” deformity
It is a hypoechoic or hyperechoic lesion of the tunica that involves its whole circumference, especially its proximal portion. Pharmacostimulation results in an hourglass shape of the shaft portion affected by fibrosis. It is not necessarily associated with a calcified plaque and may merely be the result of a circular lesion of the tunica [8].
Negative US findings in presence of a clinically palpable plaque are frequently reported, but have not been specifically investigated.
47.1.1 Colour Doppler Penile Ultrasonography
Colour Doppler penile ultrasonography is another useful US modality in the workup of suspected PD. It provides information on lesion morphology, structure and size as well as on vascular erectile function. The accuracy of US imaging, hence its diagnostic performance, depends on operator skill and equipment type. As in other US diagnostic modalities, there is a fairly steep learning curve. The scanner should be a last-generation machine endowed with the most recent image processing algorithms and a 5–12 MHz linear array transducer.
Before beginning the examination with the patient in supine position, accurate palpation is important since it allows to locate the plaque (or plaques in multifocal disease), assess its consistency and make a rough evaluation of its size, to form an idea of what will be depicted on the screen. Longitudinal and transverse scans need to be obtained along the ventral and dorsal aspects of the penis, including the urethral bulb and the crura by passing the transducer under the scrotum and along the perineum. All penile structures need to be assessed, including the tunica albuginea, corpora cavernosa, corpus spongiosum and glans, before evaluating the plaque(s). The examination consists of two phases, baseline and dynamic. The baseline phase involves investigation of tunica thickening (diffuse or localized); identification of plaque number, site and size; and assessment of any septum involvement. Longitudinal and transverse diameter and thickness are then measured, and plaque volume is calculated, usually automatically by the scanner. Any calcifications need to be identified, counted and individually measured for size. Plaque size and calcification are the main parameters to assess response to therapy.
The dynamic phase begins with intracavernosal injection of PGE1 (usual dose 2.5/10 μcg). Spectral Doppler is essential to measure flow velocity at the level of the cavernous arteries and is commonly evaluated from the penile base, where the Doppler angle ensures more accurate measurement. Colour Doppler examination allows measuring peak systolic velocity (PSV) and end-diastolic velocity (EDV), which enable calculation of the resistance index (RI) and detection of normal helicine arteries and any cavernosum-spongiosum or cavernosum superficial shunting. Such measurements are performed at precise intervals, usually 5, 15 and 30 min from PGE1 injection.
The erection induced in the dynamic phase also enables a photograph to be taken and calculation of the so-called angle of curvature, another useful measure for follow-up evaluation.
The subsequent morphological colour/power Doppler study of the microcirculation provides information on any associated vascular deficits, especially in patients with vasculopathy, diabetes or cardiovascular risk factors, where the three branches of the helicine arteries are difficult to depict if their angle is <90°, a finding that in turn is responsible for erectile dysfunction due to predominantly distal arterial disease.
The dynamic phase also depicts any site-specific venous leakage around the plaques – i.e. venous outflow on the edges of the hyperechoic lesion – which develops about 12 months from disease onset in patients with erectile dysfunction and a veno-occlusive defect documented by Doppler ultrasonography. These findings are seen in 12–20 % of patients and are responsible for secondary venous outflow [9] (Fig. 47.4).
Fig. 47.4
Site-specific leak
In some patients with severe PD, persistent cavernosum-spongiosum shunts seen close to the plaques are associated with a higher PSV and a lower RI compared with the other cavernosum-spongiosum shunts, supporting the hypothesis that blood loss may also occur through these vessels [10].
According to some studies, Doppler examination can detect hyperperfusion around the plaques as a sign of inflammation in the active disease stage, whereas the absence of colour signal around them should be considered as a sign of disease stabilization [11, 12].
The most common vascular abnormality seen in PD patients is impaired veno-occlusive function [13]. In particular, they present an increased incidence of venous leakage than their peers [14]. Whereas in normal erection the venules draining the corpora cavernosa are passively compressed by the expanded cavernosal tissue and the tunica albuginea, in PD patients the reduced elasticity of the tunica albuginea limits such stretching, preventing vein compression. As a consequence, Doppler flowmetry shows high diastolic velocity throughout the examination, with lower than normal RI values [15]. The severity of the veno-occlusive impairment is proportional to plaque extension and disease stage.
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