MR imaging of the prostate gland: normal anatomy

MR images of the male pelvis in 55 subjects were analyzed retrospectively for depiction of the zonal anatomy of the prostate gland as related to different repetition (TR) and echo (TE) times, slice thickness, plane of imaging, chronologic age of the patient, and different magnetic field strengths. With imagers operating at 0.35 and 1.5 T, T2-based tissue-contrast images were needed for the demonstration of the internal anatomy of the prostate gland. The display of zonal anatomy was improved when continuous 0.5-cm slices were used. Evaluating sequential sections, the peripheral, central, and transition zones could be differentiated. The peripheral zone showed higher signal intensity than either the central or transition zone and was discerned in the coronal, sagittal, and transverse planes. The central zone was of low signal intensity and was well displayed in the coronal and sagittal planes. The central zone was seen in 31 of the 32 young men (aged 25-35 years) but in only eight of the 23 older men (aged 40 years and older). The transition zone had intrinsic MR parameters similar to the central zone, and the two could be distinguished from each other only by the knowledge of their respective anatomic location. The low-intensity transition zone blended with the periurethral glands and the preprostatic sphincter. The transition zone was of homogeneous low signal intensity in young men but varied in size and signal intensity in older men. Such a detailed display of the prostate zonal anatomy offers a unique potential for the evaluation of prostatic physiology and disease.     

MR imaging of the scrotum: pathologic conditions

The utility of high-resolution magnetic resonance (MR) imaging in studying a variety of intratesticular and extratesticular pathologic conditions was assessed. The high magnetic signal intensity of the testis provided an excellent background for visualization of intratesticular abnormalities. Except for old blood, all intratesticular processes were less intense than testis, especially on T2-weighted images. The visualization of the tunica albuginea is a distinct advantage, allowing its assessment in cases of trauma or testicular tumors. Epididymal and spermatic cord abnormalities were easily recognized. All pathologic conditions were best seen on T2-weighted images acquired in the coronal plane. Balanced images allowed for tissue characterization.     

High-resolution MR imaging of the cadaveric human spinal cord: normal anatomy

The purpose of this study was to demonstrate the regional MR anatomy of a normal human spinal cord under near optimal conditions. A spinal cord and meninges were excised and segments from the cervical (C6), thoracic (T6), lumbar (L3), and sacral/cauda equina regions were examined on a 2-T MR system. By using a 2.5 x 2.0 cm solenoid coil and a multislice spin-echo sequence, we achieved a resolution of 58 microns in the readout direction and 117 microns in the phase-encode direction. Histological sections corresponding to the areas imaged by MR were retained and treated with stains that demonstrated the distributions of collagen (hematoxylin, phloxine, saffron), myelin (Luxol fast blue/H and E), or neuritic processes (Bielschowsky's). Subarachnoid vascular, white matter, and gray matter structures were demonstrated by MR and light microscopy. The resulting MR images and photomicrographs were correlated. Different signal intensities were observed in the gracile and cuneate fasciculi, and these differences were similar to the pattern seen with the myelin stain. Decreased signal intensity was present in the region of the spinocerebellar tracts. The anatomic detail demonstrated by this study was clearly superior to that shown by clinical MR examinations.     

MR imaging of the intraparotid facial nerve: normal anatomy and pathology

Three normal volunteers, 58 normal patients, and three patients with parotid tumors were studied with a 0.3 T permanent-magnet imaging system to directly image the intraparotid facial nerve. On T1-weighted images the nerve appeared as a curvilinear structure of relatively low signal intensity within the fatty, high-signal parotid parenchyma. Its major divisions and branches could be imaged only with specially angled axial scan planes. To verify our observations MR imaging was compared with whole-organ cryomicrotome sections cut at the same angles. Normal variations in the appearance of the nerve and pitfalls in its visualization are discussed. Three cases of parotid tumors, with surgical confirmation of the relationship of the facial nerve to the tumor, are presented. MR is the only imaging technique capable of direct imaging of the facial nerve in the parotid bed: it may assist materially in the surgical management of tumors of the parotid gland.     

MR imaging of the finger tendons: normal anatomy and commonly encountered pathology

MR imaging has emerged as a powerful tool in the evaluation of soft tissue structures such as the tendons of the hand and finger due to its excellent soft tissue contrast and multiplanar imaging capabilities. In the finger and hand, perhaps more than in any other location in the body, a detailed and intimate understanding of anatomy is crucial for lesion localization, directing clinical management and predicting long-term prognosis. These issues are of paramount importance to both the clinician and imager, both faced with the challenge of the complex anatomy and pathology associated with these delicate structures. The anatomy of the finger including intrinsic and extrinsic muscles, retinacular structures, and tendons will be discussed. The MR imaging features of common lesions of the tendons of the hand and finger will be reviewed.     

Heating of the scrotum by high-field-strength MR imaging

Sterility can occur in mammals if spermatogenic tissue is acutely or chronically heated to levels equal to or greater than body temperature. High-field-strength MR imaging has been shown to elevate tissue temperatures, particularly if high levels of RF radiation are used. To determine if MR imaging above the recommended level for RF radiation is associated with heating of the scrotum, scrotal skin temperatures were measured in eight subjects immediately before and after MR imaging of the scrotum with a 1.5-T, 64-MHz MR scanner at mean whole-body average specific absorption rates ranging from 0.56 to 0.84 W/kg (mean, 0.72 W/kg). The average imaging time was 23 min. A statistically significant (p less than .01) increase in average scrotal skin temperature was associated with MR imaging (before MR imaging, 30.8 degrees C; after MR imaging, 32.3 degrees C). The largest change in temperature was 3.0 degrees C, and the highest temperature measured was 34.1 degrees C. MR imaging at relatively high specific absorption rates produced a statistically significant increase in average scrotal skin temperature. However, the recorded temperatures were below the threshold known to affect spermatogenesis in mammals.     

Human fetal anatomy: MR imaging

Twenty-four pregnant women carrying 26 fetuses (two sets of twins) were imaged with magnetic resonance (MR) imaging at 0.35 T following sonographic evaluation. Each study was retrospectively evaluated to determine which of 33 normal fetal structures were visible on the images and which imaging parameters were most useful for depicting fetal anatomy. Fetal motion degraded fetal images in all but two cases, both with oligohydramnios and in the third trimester of gestation. Nevertheless, many fetal structures were identifiable, particularly in the third trimester. Visualization of fetal anatomy improved with intravenous maternal sedation in five cases. Relatively T1-weighted images occasionally offered the advantage of less image degradation owing to fetal motion and improved contrast between different fetal structures. More T2 weighting was believed to be advantageous in one case for outlining the fetal head and in one case for delineation of the brain. In many cases, structures were similarly identifiable (though with different signal intensities) regardless of the parameters selected. The authors conclude that MR imaging of many fetal structures is currently unsatisfactory and is probably of limited value, particularly in the first and second trimesters. However, the relative frequency and detail with which the fetal head and liver can be depicted indicate that these may be areas for further investigation, and the potential utility of imaging fetal fat warrants further investigation.     

Esophageal imaging by MR and CT: study of normal anatomy and neoplasms

In 20 patients with normal esophagi, spin-echo magnetic resonance (MR) imaging was performed to determine the appearance at different pulse sequences and T1 and T2 values. Twelve patients with esophageal carcinoma were also studied by both MR and computed tomography (CT); in ten, there was correlation with surgical and pathologic findings. Both MR and CT showed low accuracy in staging the tumors (40% and 70%, respectively), mainly because of difficulty in detecting tumor invasion through the muscle layer into periesophageal fat. Relatively T1-weighted images (repetition time, 0.5 second; echo time, 28 msec) were best for depiction of both normal esophageal anatomy and esophageal tumors. T1 and T2 measurements varied widely for both normal and abnormal esophagi and thus were not useful in predicting histologic findings.     

MR imaging: vascular anatomy of the abdomen

In support of the thesis that MRI may replace more invasive angiography in some applications, a total of 28 MR sections are presented to illustrate the vascular anatomy of the abdomen in coronal, transverse and sagittal planes. More than 20 vessels are identified ranging in size from the aorta to the left inferior adrenal vein and the spermatic veins. There is no anatomic continuity in sections made in the coronal and transverse planes; sequential sections of a single patient are presented in sagittal and parasagittal planes, however. The polarity of the images is reversed for ease of comparison with angiograms.     

Testes and scrotum: MR imaging at 1.5 T

Magnetic resonance (MR) images of the scrotum were obtained at 1.5 T in 20 subjects, 13 patients with intrascrotal pathologic conditions and seven healthy subjects. Characteristic MR imaging signals obtained on T1- and T2-weighted images allowed differentiation of testis from epididymis and spermatic cord. Masses were differentiated from normal testicular parenchyma in all cases. Atrophic or ischemic testes had lower signal intensity than normal testes on T2-weighted images. Hematoma displayed a characteristic high intensity on both T1- and T2-weighted images. Intratesticular and extratesticular pathologic conditions were readily differentiated. These results suggest that MR imaging is useful in the diagnosis of scrotal and testicular abnormalities.     

Retropharyngeal space: evaluation of normal anatomy and diseases with CT and MR imaging

A retrospective analysis of computed tomographic (CT) and magnetic resonance (MR) images and clinical records of 39 patients with retropharyngeal space (RPS) lesions was completed. The review was undertaken to answer the following questions: (a) what is the spectrum of lesions of the RPS? (b) what imaging features mark a lesion as originating in the RPS? and (c) is there a difference between the radiologic pattern of the suprahyoid and infrahyoid portions of the neck? Of the 39 patients in the study, nine had RPS infections, 17 had RPS malignancies, two had benign tumors, seven had RPS pseudotumors, and four had hematoma or air in the RPS after trauma. RPS lesions demonstrated two distinct radiologic patterns: a nodal pattern and a nonnodal pattern. The nodal pattern, found only in the suprahyoid neck, occurs when infection or tumor begins in the lymph nodes of the RPS. The lesions may be unilateral or bilateral, but the middle part of the RPS is spared. The nonnodal pattern, found primarily in the infrahyoid RPS, results when the infection or tumor directly invades the RPS or goes beyond the nodes of the RPS. The nonnodal lesion appears rectangular and spans the RPS from side to side.     

MR imaging of the cervical spine: neurovascular anatomy

High-resolution surface-coil MR imaging reveals intricate anatomic detail of the cervical spinal canal and its neurovascular contents. Appreciation of the normal neurovascular anatomy provides a scientific foundation for the detection of disease. Sagittal, axial, and oblique MR images of normal subjects were correlated with comparable anatomic sections obtained with a cryomicrotome whole-organ sectioning technique. The anterior epidural venous plexus is a prominent structure in the cervical spinal canal and was consistently identified both with cryomicrotomy and with MR in sagittal and axial planes. Epidural veins can be displaced and distorted in patients with cervical disk disease. Nerve roots including dorsal and ventral rootlets were consistently identified on axial images coursing through the subarachnoid space. Oblique-plane imaging showed nerve roots "en face" in their respective foramina; this may be a useful imaging technique in the diagnosis of nerve root impingement.     

Normal anorectum: dynamic MR imaging anatomy

In this study, the anatomy of the anorectum in relation to the surrounding structures and the anorectal angle were analyzed with magnetic resonance (MR) imaging at rest, during perineal contraction, and during straining in 10 asymptomatic subjects. The intra- and inter-observer and intra- and interpatient variations in the measurements of the anorectal angle, position of the anorectal junction, and position of the plica of Kohlrausch in the rectum were established at rest, during perineal contraction, and during straining. The values for the anorectal angle and position of the anorectal junction obtained with MR imaging were compared with standard radiography defecography findings. It was shown that MR imaging has the potential for measuring these parameters in a more precise and more patient-friendly way than defecography. Unlike dynamic defecography, MR imaging is able to depict the mobility of the posterior rectal wall. A descent of over 20 mm from rest to straining should be considered pathologic. This finding might play a role in patient selection for operation.     

MR imaging of the scrotum with a high-resolution surface coil

Magnetic resonance (MR) imaging of the scrotum with a high-resolution surface coil was performed in ten healthy volunteers and 20 patients with scrotal abnormalities demonstrated by high-resolution real-time ultrasound (US). Four patients had an abnormal testis (two tumors, one cyst, one testicular atrophy), and 16 patients had extratesticular abnormalities (four hydroceles, five epididymal cysts, one hernia, and six cases of epididymitis). The normal structures of the scrotum were depicted clearly on MR images. In all cases, the tunica albuginea was easily differentiated from the testis and epididymis. MR imaging enabled one to distinguish intratesticular from extratesticular lesions and to determine whether a lesion was solid or cystic. Complicated and simple fluid collections could also be differentiated. In general, MR imaging and US scanning provided similar information. A potential advantage of MR imaging is in the evaluation of patients with painful scrotal lesions that may limit US evaluation.     

MR imaging anatomy of the optic pathways

Imaging in neuro-ophthalmology is a major, developing field. Visual and motor ocular symptoms and signs are of diagnostic and localizing significance, and occur frequently in patients with brain space-occupying lesions. Knowledge of the anatomy of the optic pathways extending from the retina to the calcarine fissure throughout the brain is crucial. Multiplanar high resolution MR imaging permits the physician to depict the visual path with exquisite detail. This article provides a correlative regional anatomic and imaging atlas of the brain following the optic pathways, with reference to the most accurate technical imaging procedures.