الفهرس 
INTRODUCTION TO DEVELOPMENT THE GENITAL SYSTEMOnly 14 pages are availabe for public view
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Abstract
Ultrasonography is the imaging modality of choice in the assessment of scrotal diseases. Its success is based on its excellent depiction of scrotal anatomy, display of testicular diseases, accuracy in distinguishing intratesticular from extratesticular lesions and determine whether the mass is cystic, solid or complex, low cost, easy accessibility, speed, and lack of ionizing radiation.
However, sonography is limited by its small field of view, high dependence on technical expertise, and lack of specificity in many conditions.
Penile ultrasonography is considered as part of the initial evaluation of patient with penile cancer and in the follow up. It is more accurate than clinical examination in staging primary and secondary penile cancers, by using the most recent apparatus that produces images with high spatial and contrast resolution, tumors circumscribed in the subepithelial tissue can be distinguished from those involving the corpora cavernosa and corpus spongiosum.
MRI adds a new dimension to the assessment of scrotal diseases. It demonstrates exquisite anatomical details of the entire scrotum and inguinal region. it allow the recognition of each intrascrotal structure on the basis of its characteristic appearance and signal intensity rather than its strict anatomic location.
MRI, with the use of high field strengths and surface coils, provides high outstanding contrast resolution as well as a wide field of view. Like ultrasonography, MRI is nonionizing and has, as yet, no known harmful effects.
The ability to recognize each intrascrotal structure (because of its signal intensity, appearance and location) separated from any other structure, the ability to view the right and left hemiscrotum with the inguinal region, and the high contrast afforded by MRI make this modality less subjective than ultrasonography.
Many disease processes have characteristic appearance that allow their recognition with sufficient specificity. Although the true sensitivity of MRI has not been substantiated, it is likely equal to or may exceed that of sonography.
The majority of pathological conditions of the scrotum are best visualized on T2-weighted images. The homogeneous, relatively high signal intensity of the normal testes of T2-weighted images provide an excellent background for visualizing intratesticular pathology. T1-weighted images allow for tissue characterization and added specificity.
Complete assessment of the scrotum is possible in most cases with coronal sections only. Axial T2-weighted images add confidence; demonstrate to a better advantage small lesions abutting the anterior or posterior surfaces and help defining complex anatomy.
The use of IV contrast aids in the assessment of testicular vascularity for great specificity and possibly the assessment of epididymis. It does aid in distinguishing cystic from solid lesions. Tumors which are typically irrecognizable on T1-weighted images become more obvious after the administration of contrast.
The differential diagnosis of intrinsic abnormalities includes tumor, infection, hemorrhage, fibrosis and infarction. To diagnose disease, one cannot rely solely on intratesticular signal intensity changes. Signal changes allow the detection of disease, but these changes must be assessed in conjunction with clinical data and other associated changes.
MRI can diagnose and distinguish torsion from epididymitis accurately. It can probably differentiate most tumors from infection. Indeed, in the acute scrotum, which can be caused by torsion, epididymitis or tumor, MRI may prove to be the most specific of all scrotal imaging modalities.
Accurate evaluation of scrotal diseases requires information about not only morphology but also testicular perfusion. Dynamic contrast-enhanced subtraction MRI can do this task excellently and superiorly to ultrasonography. A new modern technique that has the capability to differentiate testicular diseases from extratesticular scrotal disorders accurately and to diagnoses scrotal disorders with high degree of specificity.
Collectively. MRI is an effective modality for detecting and differentiating the full range of disease entities involving the scrotum due to high intrinsic soft tissue contrast resolution, wide field of view and multiplanner imaging. However, at present, MRI provides information similar to that obtained with ultrasonography in most cases. Therefore ultrasonography remains the procedure of choice for evaluating scrotal pathology due to its ease of performance, acceptable accuracy and lower cost. High cost, limited accessibility and rarity of efficient reporters save MRI to equivocal cases and painful scrotal diseases whereas sonographic examination requires good contact with scrotal surface.
Although ultrasonography has been primary modality for cross-sectional imaging of the penis, the superior soft-tissue contrast and spatial resolution afforded by magnetic resonance provide opportunity to advance imaging evaluation of this organ .in general neither MR nor other imaging is needed for the diagnosis of penile tumor because they usually visible at physical examination MR imaging may be performed for staging purposes.