Nonpalpable testes in young boys: evaluation with MR imaging

A prospective evaluation of magnetic resonance (MR) imaging for localization of a nonpalpable testis was performed in 24 boys aged 11 months to 6 years. Definitive surgical follow-up was obtained for 15 nonpalpable testes in 14 patients who form the basis of this study. MR imaging correctly indicated the unilateral absence of a testis in six of seven patients prospectively and all seven patients retrospectively. Surgically localized undescended testes were identified with MR imaging in five of eight cases prospectively and seven of eight cases retrospectively. Like scrotal testes, undescended testes were hypointense to fat on sequences with a short repetition time (TR) and echo time (TE) in all cases, and hyperintense or isointense to fat on long TR/TE sequences in all but two cases. Inguinal testes were located along the course of a linear low-signal-intensity structure that extended to the scrotum, which may represent the remnant of the gubernaculum testis. A low-signal-intensity band through the testis, presumably the mediastinum testis, was seen in five of the undescended testes. Although MR imaging can often be used to localize a nonpalpable testis, currently MR is not sensitive enough to allow complete exclusion of the diagnosis of an undescended testis; thus failure to localize a testis with MR imaging should not defer laparoscopy or surgical exploration when indicated.     

Recurrent thyroid carcinoma: characteristics on MR images

Magnetic resonance (MR) imaging was used in 32 patients, including eight with benign disease, after partial or total thyroidectomy to determine sensitivity and specificity of MR imaging in the detection of tumor recurrence, to compare signal intensities of scar versus recurrent tumor qualitatively and quantitatively, and to define the extent of recurrent tumor. Findings from surgery (n = 23), needle biopsy (n = 1), or clinical follow-up (n = 8) were used for verification. Of 24 patients with primary thyroid carcinoma, 15 had recurrence and nine had a normal postsurgical thyroid bed. Diagnosis from MR images was correct in 20 cases, but false positive in three and false negative in one. Local recurrence was characterized by low to medium intensity on short repetition time (TR)/short echo time (TE) images and medium to high intensity on long TR/long TE images. Scar in the normal postsurgical thyroid bed showed low intensity on both short and long TR/TE images. Local recurrence of thyroid carcinoma and lymph node metastasis produced positive contrast compared with muscle on short TR/short TE (31 + 19%) and long TR/long TE (85 + 30%) images; fibrosis produced negative contrast, particularly on long TR/long TE (-56, -80%) images. These results indicate the capability of MR imaging in the evaluation of recurrence of thyroid tumors and in the differentiation of abnormal tissue due to tumor recurrence from postoperative fibrosis by means of signal contrast relative to a reference tissue.     

CT and MR imaging of malignant germ cell tumor of the undescended testis

Preoperative localization of the impalpable undescended testis is necessary to facilitate proper surgical planning. There is an increased incidence of malignant change in the undescended testis; demonstration of malignancy before surgery will significantly alter the treatment. We describe the computed tomographic (CT) and magnetic resonance (MR) findings in 2 patients with malignant change in an intraabdominal testis. The CT scan revealed lesions with areas of low density, 1 of which had focal calcifications; MR revealed lesions of predominantly low or intermediate signal intensity on both long and short TR/TE images, with some areas of very high signal on both sequences. After initial management with chemotherapy, the residual tumor was surgically resected. In neither instance was residual normal testis demonstrated. Both CT and MR are ideal methods of examining malignant transformation of the undescended testis, because of their ability to characterize the internal structure of the organ and, in the case of MR, its capacity for multiplanar imaging. They are almost of equal value except for the ability of CT to identify calcification and of MR to diagnose hemorrhage.     

CT and MR imaging of malignant germ cell tumor of the undescended testis

Preoperative localization of the impalpable undescended testis is necessary to facilitate proper surgical planning. There is an increased incidence of malignant change in the undescended testis; demonstration of malignancy before surgery will significantly alter the treatment. We describe the computed tomographic (CT) and magnetic resonance (MR) findings in 2 patients with malignant change in an intraabdominal testis. The CT scan revealed lesions with areas of low density, 1 of which had focal calcifications; MR revealed lesions of predominantly low or intermediate signal intensity on both long and short TR/TE images, with some areas of very high signal on both sequences. After initial management with chemotherapy, the residual tumor was surgically resected. In neither instance was residual normal testis demonstrated. Both CT and MR are ideal methods of examining malignant transformation of the undescended testis, because of their ability to characterize the internal structure of the organ and, in the case of MR, its capacity for multiplanar imaging. They are almost of equal value except for the ability of CT to identify calcification and of MR to diagnose hemorrhage.     

磁共振在未降睾丸诊断中的临床价值初探

目的评价ＭＲＩ对未降睾丸的诊断价值。方法对１５例年龄在１～２８岁、临床不可触及的未降睾丸病人行ＭＲＩ检查，均经手术证实。结果所有未降睾丸（１８枚）均由ＭＲＩ正确显示，１５例中，３例为双侧，１２例为单侧。结论ＭＲＩ具有无创性、无辐射性，且能多方位成像的特性。本组病例证实其为未降睾丸定位的一种非常有用的影像手段，ＭＲ影像能揭示未降睾丸的解剖及组织学特征，最佳的成像平面为横断位及冠状位，ＧｄＤＴＰＡ增强有助于未降睾丸的显示     

MR imaging of intracranial metastatic melanoma

Ten patients with intracerebral metastases from malignant melanoma were evaluated with magnetic resonance (MR) imaging performed at 1.5 T using spin-echo techniques. On the basis of histopathologic findings in three of 10 cases and CT appearances in all 10 cases, three patterns were identified on analysis of MR signal intensities in both short repetition time/echo time (TR/TE) and long TR/TE spin-echo scans. In comparison to normal cortex, nonhemorrhagic melanotic melanoma appeared markedly hyperintense on short TR/TE images and isointense, mildly hypointense on long TR/TE images. Nonhemorrhagic, amelanotic melanoma appeared isointense or mildly hypointense on short TR/TE and isointense or mildly hyperintense on long TR/TE images. Hemorrhagic melanoma varied in appearance, depending on the stage of hemorrhage. Melanotic, nonhemorrhagic melanoma can be distinguished from early and late subacute hemorrhage by its signal intensity on long TR/TE images. Spin-echo MR appears to be the method of choice for diagnosing melanotic metastases.     

MR imaging of the dilated biliary tract

The magnetic resonance (MR) examinations of 18 patients with dilated bile ducts were reviewed retrospectively to determine the capability of MR to demonstrate biliary dilatation, assess MR appearance of the dilated biliary tract using spin-echo techniques, and define the optimal MR imaging parameters (repetition time [TR] and echo time [TE]) for its demonstration. On images with short TR (0.5 sec) and TE (28 msec), the dilated intrahepatic and intrapancreatic bile ducts usually had lower signal intensity compared with the surrounding liver or pancreas; on images with long TR (2.0 sec) and TE (56 msec), they had higher signal intensity. Because of the observed variation in percentage of contrast between dilated bile ducts and surrounding liver and pancreas, two imaging sequences are recommended to obtain reliable demonstration of dilated intrahepatic and intrapancreatic bile ducts. The dilated common bile duct at the level of the hepatic hilus is best seen with a short TR and TE.     

MR signal intensity of parathyroid adenomas: correlation with histopathology

Recent experience has shown that parathyroid adenomas vary in their MR signal intensity, which raises the question of whether the signal intensity is related to different histologic characteristics. In order to address this question, 10 patients who had MR imaging studies (four at 0.35 T, six at 1.5 T) showing large- to medium-sized parathyroid adenomas and who subsequently underwent surgery with histologic proof of the lesion were evaluated. The MR appearance was compared with histologic characteristics. The adenomas were classified into three groups according to the MR appearance: group I, low signal intensity on short TR/TE images, high signal intensity on long TR/TE images (n = 5); group II, low signal intensity on short and long TR/TE images (n = 3); group III, high signal intensity on short and long TR/TE images (n = 2). Histologic analysis revealed that the major features of each group were different. High cellularity without degeneration or fibrosis was observed for all five adenomas from group I. In group II, all three adenomas showed cellular degenerative changes, old hemorrhage with hemosiderin-loaded macrophages, and/or fibrosis. In group III, both adenomas showed evidence of acute hemorrhage without significant degenerative or fibrotic changes. These data suggest that the signal intensity of parathyroid adenomas on T1- and T2-weighted images corresponds at least in part to differences in histologic composition.     

Painful sickle cell crisis: bone marrow patterns observed with MR imaging

Eleven patients with homozygous sickle cell anemia (SCA) undergoing painful crisis were studied with magnetic resonance (MR) imaging. The signal intensity of bone marrow was diffusely decreased in the axial and peripheral skeleton on short repetition time (TR)/echo time (TE) images and long TR/TE images, which suggested hematopoietic marrow hyperplasia and was confirmed by isotope marrow scans in five patients. Focal areas of further decrease in signal intensity were seen on short TR/TE images in 12 of the 14 (86%) painful joints and three of the five (60%) painless joints. In the painful joints, these focal areas converted to high signal intensity on long TR/TE images, presumably due to edema, which suggested acute marrow infarction. In the painless joints, these low-intensity focal areas remained as low signal on long TR/TE images, which suggested absence of edema and thus areas of old infarction or fibrosis. These results indicate that MR imaging may enable differentiation between acute and chronic marrow infarcts in patients with SCA and serve as a useful guide in monitoring and directing therapy.     

未降睾丸并精原细胞瘤的MRI诊断

目的 探讨未降睾丸并精原细胞瘤的ＭＲＩ特点,以期提高对本病的认识。材料与方法 ３例经病理证实的未降睾丸精原细胞瘤,采用Ｓｈｉｍａｄｚｕ５０Ｘ／Ｈ型磁共振仪,０．５Ｔ,超导,术前行ＭＲＩ平扫及增强扫描。结果 ３例均为单侧腹腔内精原细胞瘤,直径分别为８ｃｍ、９ｃｍ及２ｃｍ,其ＭＲＩ特点包括：⑴阴囊内单侧或双侧睾丸缺如并腹内肿块;⑵肿块常较大;⑶信号强度不均,常有出血、钙化及坏死;⑷恶变的未降睾丸可有完     

Preliminary clinical results with low flip angle spin-echo MR imaging of the head and neck

A new approach for producing primarily T2- and proton-density-weighted MR images in less time than the conventional long TR, long TE imaging is to reduce the TR of a double spin-echo pulse sequence and to also reduce the RF excitation flip angle to minimize the resulting T1 sensitivity. In preliminary studies with a human volunteer and five patients with various diseases of the head and neck, conventional long TR, long TE and short TR, short TE images were compared with short TR, long TE images with reduced flip angles (45 degrees, 30 degrees), which required only 40% of the imaging time of the long TR images. The latter images showed a similar contrast pattern to the conventional T2-weighted image, and contrast-to-noise measurements indicated an increase in contrast between the lesion and nearby tissue when the flip angle was reduced. Furthermore, the maximum contrast/noise per unit imaging time on the short TR, long TE image was comparable to that on the long TR, long TE image. Optimization of the flip angle with short TR allows a substantial reduction in imaging time but with a reduction in multislice capability. This technique will be most useful in areas of complex anatomy where two or more orthogonal imaging planes are required, such as the head and neck.     

Inverted papilloma: evaluation with MR imaging.

The authors examined the magnetic resonance (MR) appearance of inverted papillomas to determine if this histologically benign lesion could be distinguished from malignancies of the sinonasal cavity. MR images in 10 patients with histologically proved inverted papilloma were retrospectively reviewed. The signal intensity of inverted papillomas on short repetition time (TR) images was iso- to slightly hypertintense to muscle in all 10 patients. Inverted papillomas had intermediate signal intensity on the long TR/echo time (TE) images. The tumors were iso- or slightly hypointense to fat on long TR/short TE images. In the seven patients who received gadopentetate dimeglumine, all inverted papillomas showed solid inhomogeneous enhancement. A review of eight sinonasal malignancies showed no distinctive signal intensity or enhancement characteristics to help differentiate inverted papillomas from various malignant tumors. The authors conclude that there is no signature MR appearance for the benign inverted papilloma. The main utility of MR imaging is in defining the extent of the lesion.     

Radiographically negative avascular necrosis: detection with MR imaging

To correlate the morphologic appearance on magnetic resonance (MR) images of radiographically negative avascular necrosis (AVN) of the femoral head with that on computed tomographic (CT) and radionuclide scans, the radiographic and clinical records of 24 patients were reviewed retrospectively. In 18 patients the MR signal intensity features were monitored by means of serial imaging. All MR studies included T1-weighted (short repetition time [TR], short echo delay time [TE] ) imaging and T2-weighted imaging (long TR, long TE). Thirty-one hips were determined with MR to be involved by AVN; 27 were staged on the basis of signal intensity characteristics within the low-intensity rim. Core decompression was performed on 18 hips. Afterward, progression of disease occurred in only one hip. Fourteen of the 16 asymptomatic patients (88%) had early-stage focal lesions. CT scans were obtained in 15 patients and radionuclide scans in 21. Ten hips at radionuclide imaging and five at CT appeared normal when MR results were distinctly abnormal. MR can depict early radiographically negative AVN in asymptomatic individuals. At this early stage, the lesions in this series appear to be nonprogressive after treatment.     

Contrast-enhanced MRI of periarticular soft-tissue changes in experimental arthritis of the rat

This study was to determine if manipulation of magnetic resonance signal intensity by means of an intravenously injected paramagnetic contrast agent is useful for the detection and characterization of periarticular inflammation. Arthritis was induced in 20 rats by means of intradermal injection of Freund's complete adjuvant. MR imaging was performed with a resistive magnet operating at 0.35 T. A double spin-echo technique with TE's of 28 and 56 ms and TR's of 0.5 and 2.0 s was used. The hindpaws of the adjuvant-injected rats were imaged on Day 8, Day 11, or Day 15 following injection of the adjuvant. The images were obtained in the transverse plane before and after intravenous injection of gadolinium-DTPA (0.2 mmol/kg). Because of their long T2 relaxation time, inflammatory lesions were characterized by high MR signal intensity on precontrast images obtained with long TR and long TE (T2-weighted images). On the other hand, because of their long T1 relaxation time, the inflammatory lesions were of relatively low intensity and not easily recognized on precontrast images obtained with short TR and short TE (T1-weighted images). Postcontrast T1-weighted images were also sensitive in detecting periarticular inflammation as a result of T1 shortening by the gadolinium-DTPA. However, in our particular model, the data did not indicate any greater MR sensitivity for detecting arthritis by means of gadolinium-DTPA enhancement.     

MR imaging of body fluid collections

To evaluate the potential of magnetic resonance (MR) to characterize body fluids in vivo, we determined the relaxation times and the relative MR signal intensities of 42 body fluid collections in 42 patients. Twelve normal volunteers served as controls. We also studied albumin solutions at different concentrations and blood at various periods in vitro. Because of their long T1 relaxation times, most nonhemorrhagic fluid collections had low to intermediate intensity on images obtained with short repetition time (TR) and short echo time (TE) settings. Although the relaxation times and relative MR signal intensities of noninfected collections differed from those of infected collections, the values overlapped. On images obtained with short TR and short TE, blood in acute hemorrhages had intermediate signal intensity and serum in subacute hemorrhagic collections was the only pathologic fluid producing high signal intensity. Because of their relatively long T2 values, all the fluid collections were intense on images obtained with long TR and long TE settings; consequently, differences in intensity were less evident than on images obtained with short TR and short TE settings. Magnetic resonance allows reliable discrimination of subacute hemorrhagic collections from collections of other types, but the differentiation between acute hemorrhagic collections; nonhemorrhagic, noninfected collections; and nonhemorrhagic, infected collections is less accurate.     

Thickened pituitary stalk on MR images in patients with diabetes insipidus and Langerhans cell histiocytosis

The MR images of four female patients with acute onset of central diabetes insipidus and pathologically confirmed Langerhans cell histiocytosis were evaluated retrospectively for evidence of lesions in the hypothalamic-pituitary axis. The examinations were conducted on a 1.5-T MR system with thin-section sagittal and coronal T1-weighted (short TR/short TE) and T2-weighted (long TR/long TE) images. Three patients underwent T1-weighted MR after IV administration of gadopentetate dimeglumine. Compared with 20 normal subjects who were evaluated with the same MR protocol, three of the four patients had a symmetrically thickened pituitary stalk that demonstrated homogeneous signal enhancement following contrast administration. The high signal intensity of the posterior lobe, which was seen in normal subjects on T1-weighted sagittal images, was absent in all four patients. Two patients had associated abnormalities on either chest films or imaging studies of the temporal bone and two patients had isolated CNS Langerhans cell histiocytosis. The combination of a thickened pituitary stalk and absent posterior pituitary hyperintensity, while nonspecific for Langerhans cell histiocytosis, should nevertheless prompt further studies, such as chest films, bone scanning, or temporal bone CT, to attempt to narrow the differential diagnosis. Gadopentetate dimeglumine, in particular, may be a useful adjunct in the MR examination of the patient with diabetes insipidus.     

MR imaging with surface coils in primary hyperparathyroidism

The use of magnetic resonance (MR) to preoperatively evaluate patients with primary hyperparathyroidism was assessed using a 1.5 T system and surface coil reception. Twenty-five patients with primary hyperparathyroidism were studied before surgical exploration. Axial images, 5 mm thick, were obtained from the thyroid cartilage to the sternal notch. Both T1-weighted [short repetition time (TR), short echo time (TE)] and T2-weighted (long TR, long TE) spin echo sequences were performed in most cases. Parathyroid adenomas typically demonstrated greater signal than surrounding tissues on T2-weighted sequences, yet demonstrated signal intensity that was less than or equal to normal thyroid tissue on T1-weighted sequences. Using these criteria, MR correctly identified 17 of 20 surgically proven parathyroid adenomas in the neck. Magnetic resonance appeared less sensitive in two patients with parathyroid hyperplasia, identifying only one of six hyperplastic glands. We conclude that MR with surface coils provides high contrast, anatomic delineation of the neck and is useful for preoperative localization of parathyroid tumors.     

Imaging of pancreatic neoplasms: comparison of MR and CT

Thirty-two patients with pathologically proved pancreatic carcinomas or cystadenomas were evaluated with MR images obtained with T1-weighted spin echo (short TR/short TE), inversion recovery, and T2-weighted spin-echo (long TR/long TE) pulse sequences. CT was used as the reference standard to determine the ability of MR to delineate normal and abnormal pancreatic anatomy and thereby to exclude or detect pancreatic malignancy. Short TR/short TE spin-echo sequences were significantly better (p less than .05) than inversion recovery or T2-weighted spin-echo sequences in resolution of both normal and abnormal anatomy. Resolution of pancreatic anatomy correlated (r = .9) with the image signal-to-noise ratio. In seven (22%) of 32 cases, MR visualized pancreatic tumors better than CT did because it showed a signal intensity difference between the tumor and normal pancreatic tissue. Overall, the slight superiority of MR over CT for tumor visualization tended to occur in larger tumors and was not statistically significant. On T1-weighted images, 63% (20 of 32) of pancreatic tumors studied had lower signal intensities than normal pancreatic tissue, whereas on T2-weighted sequences (TE = 60, 120, and 180 msec) only 41% (13 of 32) of tumors had increased signal intensities. Currently available MR imaging techniques offer no significant advantages over CT for evaluating the pancreas for neoplasia.     

Pigmented villonodular synovitis: a report of MR imaging in two cases

Although magnetic resonance (MR) imaging has been used to evaluate many musculoskeletal lesions, the MR appearance of pigmented villonodular synovitis (PVNS) has not been described in detail. The authors describe two cases of PVNS in the knee imaged with both computed tomography and MR. In both cases parts of each lesion had very low signal intensity on both short repetition time (TR)/echo time (TE) sequences and long TR/TE sequences. Other portions of both lesions had intermediate signal intensity (equal to or higher than that of muscle but lower than that of fat) on short TR/TE sequences and increasing signal intensity on longer TR/TE images. In one case, the lesion also had a cystic component that showed MR changes typical of complex fluid. The authors propose that the MR signal characteristics demonstrated in these cases may be explained by the unique tissue components of the lesion, particularly hemosiderin and fat.     

Pulmonary arteriovenous malformations: diagnosis by gradient-refocused MR imaging

Six known or suspected pulmonary arteriovenous malformations (AVMs) in four patients were evaluated with magnetic resonance (MR) imaging at 1.5 T. All lesions were imaged using a gradient-refocused echo pulse sequence with a 25/13 ms [repetition (TR)/echo (TE) times] and a 30 degrees flip angle, as well as with a cardiac-gated spin echo short TR/TE pulse sequence technique. Five of the lesions were vascular in nature based on their signal intensity characteristics, and one nonvascular lesion was a carcinoid tumor. On the spin echo images, the AVMs showed a central signal intensity void with a peripheral rim of intermediate signal intensity that was detectable for lesions greater than or equal to 1.5 cm in size. Smaller lesions were more difficult to distinguish from the surrounding air-filled lung, which normally generates no appreciable signal on MR images. The AVMs demonstrated uniform high signal intensity on the gradient echo pulse sequence and were more conspicuous, irrespective of size. With a single breath-hold scan, the vascular nature of the lesion could be rapidly confirmed with an acquisition time of 13 s. In three patients, the cine MR gradient echo images showed a pulsatile quality to the signal intensity in the lesion over the cardiac cycle similar to that within adjacent pulmonary vessels. The results of this study show a potential role for gradient echo MR imaging as a rapid, noninvasive method to evaluate the vascular nature of an atypical pulmonary nodule.