von Hippel-Lindau disease: radiologic screening for visceral manifestations

The visceral manifestations of von Hippel-Lindau (VHL) disease can cause significant morbidity and mortality. The authors prospectively screened 37 persons from a single kindred. Twenty-five subjects underwent abdominal ultrasound (US), contrast material-enhanced abdominal computed tomography (CT), and nonenhanced abdominal magnetic resonance (MR) imaging. Eight subjects younger than 16 years of age underwent abdominal US and MR imaging only. Scrotal US was employed in 25 male patients. Eleven subjects had renal cysts or tumors. Contrast-enhanced CT depicted renal abnormalities in 10 of these subjects, US in seven, and MR imaging in nine. Among 12 subjects with pancreatic cysts or tumors, CT showed pancreatic abnormalities in all 12, US in nine, and MR imaging in nine. Three subjects (mean age, 34.5 years) had renal tumors, and three had pancreatic masses. Scrotal US revealed epididymal cystadenomas in seven subjects; two of these tumors were surgically verified. A combination of contrast-enhanced CT and scrotal US in male patients appears to be the best way to screen for visceral manifestations of VHL disease.

Gastrinomas: comparison of MR imaging with CT, angiography, and US

In this prospective study, magnetic resonance (MR) imaging was used to localize gastrinoma in 24 patients with Zollinger-Ellison syndrome. The results were confirmed by means of either surgery or percutaneous liver biopsy and compared with results of computed tomographic (CT) scanning, selective abdominal angiography, and abdominal ultrasound (US). For primary extrahepatic gastrinoma (intra-or extrapancreatic), MR imaging had a sensitivity of 20% and a specificity of 100%, with a positive predictive value of 100% and a negative predictive value of 11%. For metastatic gastrinoma in the liver, MR imaging had a sensitivity of 43% and a specificity of 100%, with a positive predictive value of 100% and a negative predictive value of 81%. The ability of MR imaging to depict extrahepatic gastrinomas was directly related to tumor size; no tumors smaller than 1 cm were detected, and 50% of tumors 3 cm or larger were detected. MR imaging was as effective as abdominal US but less effective than either CT scanning or selective abdominal angiography for the detection of extrahepatic gastrinoma. In seven patients with hepatic gastrinoma, three gastrinomas were detected with MR imaging and with abdominal US, while five were detected with CT scanning and with selective abdominal angiography. These results indicate that, at the present time, MR imaging is generally not useful in the initial attempt to localize gastrinomas.

Gadolinium-DTPA enhanced dynamic MR imaging in the evaluation of cisplatinum nephrotoxicity

Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) enhanced dynamic magnetic resonance (MR) imaging was used to monitor the nephrotoxic effects of cis-platinum (cis-diamminedichloroplatinum; CDDP), a chemotherapeutic agent that produces damage in the proximal convoluted tubule. Ten New Zealand white rabbits (NZWs) were divided into two groups and were evaluated at two clinically relevant doses of CDDP. Group 1 (four NZWs) received CDDP intravenously at 125 mg/m2 over 1 h. Rabbits in Group 2 (six NZWs) were infused with CDDP at 40 mg/m2 each day for 5 consecutive days. Dynamic MR images were performed in the axial plane at 1.5 T using a gradient recalled acquisition in the steady state sequence with an echo time of 11 ms, a repetition time of 20 ms, and a flip angle of 10 degrees after a bolus injection of Gd-DTPA 0.1 mmol/kg. Thirty-two sequential post Gd-DTPA images (5.12 s/image) were obtained over 2 min 45 s at a single location. All rabbits underwent baseline normal and serial post CDDP Gd-DTPA enhanced dynamic MR scans. Analysis of the alterations in the normal pattern of renal enhancement caused by CDDP was facilitated by using a stacked profile image and quantitative region of interest measurements of signal intensity. Normally, after the injection of Gd-DTPA, a dark band promptly appears in the outer cortex of the kidneys and migrates centripetally toward the papilla, reflecting the tubular concentration of Gd-DTPA. In Group 1 rabbits, nephrotoxicity due to CDDP was observed as early as 9 h after administration of the drug, with a complete disappearance of the dark band by 7 days. In Group 2 rabbits, the band disappeared gradually and reappeared 2-10 days after the completion of CDDP treatment, indicative of tubular damage and recovery with return of the concentrating ability of the kidney. These results illustrate the feasibility of using Gd-DTPA dynamic MR as a sensitive monitor of drug induced alterations of renal function.

Dynamic Gd-DTPA-enhanced MR imaging of the kidney: experimental results

To determine the normal appearance of dynamic enhanced renal magnetic resonance (MR) images, 25 rabbits were injected with Gd-DTPA and 32 consecutive gradient-recalled images were acquired. Several rabbits were also imaged in dehydrated (five animals) and overhydrated (seven animals) states. A reproducible renal enhancement pattern is observed that can be divided into three phases. During the first phase, a peripheral dark band appears, probably representing arrival of Gd-DTPA within the arterioles and vasa recta. The second phase begins as a second dark band migrating centripetally toward the medulla; this likely represents the concentration of Gd-DTPA in the descending limb of the loop of Henle. The third phase is characterized by a gradual darkening in the papilla, probably caused by concentration of Gd-DTPA within the collecting ducts. Hydration status influences the duration of these phases. These observations can be explained by the anatomy and physiologic characteristics of the nephron, as well as the MR characteristics of Gd-DTPA at different concentrations.

Prospective evaluation of hepatic imaging studies in the detection of colorectal metastases: correlation with surgical findings

Nineteen patients with isolated colorectal liver metastases were preoperatively evaluated with five hepatic imaging studies. The results of these studies were correlated with operative findings. One study involved the use of EOE-13, an intravenously administered lipid contrast agent that enhances liver parenchyma on computed tomography (CT) scans (EOE-CT). Another study, arterial portography (AP-CT), was performed with injection of a water-soluble contrast agent into the superior mesenteric artery during CT scanning. Delayed CT scanning (DS-CT) was completed 4 hours after AP-CT. In addition, T1- and T2-weighted magnetic resonance imaging (MRI) (T1-MRI, T2-MRI) scans were done. All patients subsequently underwent laparotomy with identification of 78 lesions. A lesion-by-lesion analysis revealed that the sensitivity of EOE-CT (83%), AP-CT (78%), DS-CT (82%), and T1-MRI (84%) was comparable. T2-MRI had a significantly lower sensitivity (64%) compared with EOE-CT, DS-CT, and T1-MRI. The false-positive rate for AP-CT was 31%, which was significantly higher than that of all other studies. The T1-MRI examination had the lowest false-positive rate and proved to be the best hepatic imaging study in the detection of colorectal metastases. EOE-CT and DS-CT were comparable, whereas AP-CT and T2-MRI proved to be inferior tests.

Liver metastases: detection with MR imaging at 0.5 and 1.5 T

Nineteen patients with known liver metastases were examined with two magnetic resonance (MR) pulse sequences at 0.5 T and three pulse sequences at 1.5 T. In addition, the patients were studied with computed tomography (CT) enhanced with ethiodized oil emulsion-13 (EOE-13). At 0.5 T a spin-echo (SE) 300/22 (repetition time/echo time, msec) sequence prospectively demonstrated 92.4% of the detectable liver metastases, while an SE 2,000/80 sequence showed 52.1% of the lesions. At 1.5 T, an SE 300/25 sequence depicted 68.3% and an SE 2,000/80 sequence 71.6%, while the more T1-weighted inversion recovery (IR) 2,000/600 (repetition time/inversion time, msec) sequence demonstrated 89.5% of the lesions. EOE-13 CT scans depicted 93.3%. These findings suggest that T1-weighted imaging is as successful at demonstrating liver metastases at 1.5 T with an IR 2,000/600 sequence as at 0.5 T with an SE 300/22 sequence. At both field strengths, MR imaging of the liver is comparable to state-of-the-art CT.

Renal calculi after shock wave lithotripsy: US evaluation with an in vitro phantom

Fragments of renal calculi from patients who had undergone extracorporeal shock wave lithotripsy (ESWL) were embedded in an in vitro tissue-equivalent ultrasound (US) phantom to assess (a) the accuracy with which such fragments could be measured; (b) the influence of stone composition, stone depth, and transducer frequency; and (c) the effect of fragment "clumping" on size determinations and acoustic shadowing. Fragments as small as 0.8 mm in diameter could be detected at 7.5 MHz, although a practical limitation of 1-2 mm for lower transducer frequencies (3.5 and 5.0 MHz) was observed. Fragment diameter tended to be overestimated with US by a mean of 1 mm. Transducers of 5 and 7.5 MHz were more accurate in determination of size than 3.5-MHz transducers. Struvite fragments were less echogenic and were therefore measured more accurately, but smaller struvite fragments were less detectable than other fragment types. Fragment "clumping" led to significant overestimation of residual stone size even when small fragments were separated by as much as the distance equal to the diameter of one fragment. This study demonstrates that even under the best circumstances the disadvantages of US in assessing residual stone disease are significant.

Fixed spinal cord: diagnosis with MR imaging

Pulsatile motion of the spinal cord was examined with phase imaging techniques. Sagittal images of the spinal cord were obtained at different times of the cardiac cycle in healthy volunteers, as well as in patients in whom the spinal cord either was tethered, was compressed, or contained an intramedullary lesion. Pulsatile velocity changes of the spinal cord, observed on the phase images, were most marked at the cervical-upper thoracic level. Cord motion was found to be significantly decreased in cases in which the cord was either tethered or compressed. Cord enlargement due to an intramedullary lesion generally did not lead to decreased cord motion. Imaging of pulsatile cord motion may be clinically useful in evaluating diseases restricting cord motion or changing the status of parenchymal compliance.

Gadolinium DTPA enhanced MR imaging of ACTH-secreting microadenomas of the pituitary gland

Gadolinium diethylenetriamine pentaacetic acid (DTPA) enhanced magnetic resonance imaging was performed in eight patients with Cushing disease and surgically proven pituitary microadenomas. A 1.5 T scanner was used with 3 mm contiguous slices. Short repetition times (TR), short echo times (TE), and long TR, long TE sequences were obtained before and serially after intravenous administration of Gd-DTPA. Three of eight (38%) microadenomas were undetectable both without and with Gd-DTPA: one post-Gd-DTPA scan was false positive on the side opposite the adenoma. Hemihypophysectomy based on a petrosal sinus adrenocorticotropic hormone (ACTH) gradient cured all three patients. Two microadenomas (25%) were visible as hypointense foci following Gd-DTPA but not on unenhanced scans. The remaining three microadenomas (38%) were seen before and after Gd-DTPA on T1-weighted images. In this small series of ACTH-producing microadenomas, one-third were seen on unenhanced 1.5 T scans, one-third were seen only after Gd-DTPA, and one-third were not imaged even with Gd-DTPA enhancement.

Short-Ti inversion-recovery pulse sequence: analysis and initial experience in cancer imaging

Inversion recovery (IR), commonly considered a pulse sequence capable of producing T1-weighted images with excellent display of normal anatomy, is versatile: The null point and peak time provide a useful, succinct summary of the properties of IR and its capacity for producing both T1- and T2-weighted images. Shortening of the inversion time (TI) and creation of a short-TI inversion-recovery (STIR) pulse sequence increases sensitivity to malignancy and other abnormalities by making the effects of prolonged T1 and T2 on signal intensity additive and by nulling the signal from fat. The authors examined over 300 patients with various malignancies and compared STIR images with T1- and T2-weighted images obtained at 0.5 T. In 43 cases, signal-difference-to-noise ratios (SD/Ns) were calculated between tumor, fat, and muscle. In general, STIR images demonstrated tumor as a conspicuously high-intensity area in a background of muted, discernible anatomic detail. The good contrast achieved with STIR sequences between tumor and fat (SD/N = 18.1) and tumor and muscle (SD/N = 12.9) consolidated into a single image the information contained separately on T1- and T2-weighted images, which facilitates efficient detection and localization of malignancy.

Meningeal carcinomatosis in the VX2 rabbit tumor model: detection with Gd-DTPA-enhanced MR imaging

Meningeal carcinomatosis developed in 14 of 14 New Zealand White rabbits after infusion of a VX2 tumor cell suspension into the cisterna magna. All died or were killed 7-15 days after inoculation. Within days of the tumor infusion, magnetic resonance (MR) imaging with gadolinium-diethylenetriaminepentaacetic acid (DTPA) at 0.5 or 1.5 T demonstrated enhancement of the cerebrospinal fluid (CSF) secondary to disruption of the blood-CSF barrier by plaquelike lesions along the meninges. Eventually, meningeal enhancement was observed along the base of the brain and cervical spine. Quantitative assessment of the contrast enhancement on T1-weighted images revealed an increase in mean signal intensity of 213% +/- 130%. Contrast enhancement was not observed in four control animals who received an infusion of cell culture medium. These results demonstrate in an animal model that contrast material-enhanced MR imaging can be used to detect meningeal carcinomatosis by revealing breakdown of the blood-CSF barrier.

Spinal cord artifacts from truncation errors during MR imaging

The significance of linear regions of altered signal intensity that appear in sagittal magnetic resonance (MR) images along the length of the spinal cord was investigated. Examinations were performed on ten healthy volunteers and one patient with spinal cord edema. A 0.5-T or a 1.5-T MR system was used. Sampling-related effects (Gibbs phenomenon) at spinal cord edges and cerebrospinal fluid interfaces can lead to different signal patterns within the spinal cord and canal. These artifacts cause problems in interpretation, especially with the use of small object-to-pixel size ratios, by obscuring anatomy and simulating pathologic conditions such as pseudosyringes. Analysis of these intensity variations and of their dependence on sampling may improve the clinical accuracy of MR imaging.

Macronodular adrenal hyperplasia in Cushing disease

Computed tomographic (CT) scans of the adrenal glands were obtained in nine patients with Cushing disease as a result of an adrenocorticotropic hormone (ACTH)-secreting pituitary adenoma and macronodular hyperplasia of the adrenal glands. The findings were compared retrospectively with those in six patients with Cushing syndrome as a result of an autonomous adrenal adenoma and 16 with Cushing syndrome as a result of ectopic ACTH production. Seven of nine patients with macronodular adrenal hyperplasia had hyperplastic adrenal glands in addition to single or multiple focal adrenal nodules. The six patients with hypercortisolism caused by an autonomous adrenal adenoma showed atrophic (four patients) or normal (two patients) ipsilateral and contralateral adrenal glands. Fourteen of 16 patients with the ectopic ACTH syndrome had hyperplasia of the adrenal glands without nodularity, and only two had focal nodules.

Differentiation of adrenal masses by magnetic resonance imaging

Eighty-one adrenal masses in 68 patients were examined with magnetic resonance imaging (MRI). Masses included nonfunctioning adenomas (17), metastases (25), adrenocortical carcinomas (10), and pheochromocytomas (23). T1-weighted pulse sequences depicted the anatomy with a resolution comparable to that of computed tomography (CT). T2-weighted pulse sequences provided some histologic specificity separating nonfunctioning adenomas with low signal-intensity from metastases with intermediate signal-intensity and pheochromocytomas with high signal-intensity. Pheochromocytomas could always be distinguished from other adrenal masses. In 20% of the cases, metastases with low signal-intensity could not be distinguished from nonfunctioning adenomas.

Contributions of magnetic resonance imaging in the evaluation of optic gliomas

Eleven patients with gliomas in the optic chiasm were studied using a 0.5 Tesla superconducting system and third generation computed tomography scanners. All tumors were identified with both modalities, but in the majority of cases, the posterior extension of the tumor and its relationship to adjacent brain, important to both prognosis and management, were shown better by magnetic resonance imaging.

Ocular and cerebral metastases in the VX2 rabbit tumor model: contrast-enhanced MR imaging

Ocular and cerebral metastases developed after the inoculation of a VX2 tumor cell suspension into the internal carotid artery of 15 rabbits. The hematogenous spread of tumor cells resulted in ocular metastases in 13 of 15 animals (86.7%) and cerebral system metastases in 14 of 15 animals (93%). Magnetic resonance (MR) imaging with Gd-DTPA demonstrated early disruption of the blood-ocular barrier and blood-brain barrier 5-7 days after infusion of tumor cells. Quantitative assessment of contrast enhancement revealed a mean increase in signal intensity of 145% +/- 51% in the anterior chambers, 102% +/- 70% for choroidal metastases, and 51% +/- 29% for central nervous system (CNS) metastases. These results indicate that contrast-enhanced MR imaging can be used to demonstrate a loss of blood-ocular barrier integrity that is similar to the breakdown of the blood-brain barrier associated with metastatic tumors to the CNS and eye.

A reproducible model of metastatic brain and ocular tumor by hematogenous inoculation of the VX2 tumor in rabbits

A metastatic brain-tumor model has been developed in rabbits by infusing the VX2 carcinoma into the internal carotid artery to simulate hematogenous dissemination of tumor. In a series of 25 New Zealand White rabbits, multiple metastases arose in the hemisphere of 24 (96%) and in the eye of 22 (92%); in all instances ocular metastases were ipsilateral to the site of infusion. Ocular metastases were visible in the anterior chamber in 80% of animals 3 to 12 days after the infusion of VX2 tumor cell suspension. All rabbits deteriorated neurologically or died by Day 15 after the inoculation. Multiple metastases were demonstrated by magnetic resonance imaging as early as 5 to 7 days after infusion of the tumor cells and were confirmed at autopsy. This technique models hematogenous metastases to the brain and eye and is useful in evaluating the response of metastases to chemotherapy and radiation therapy directed to the brain and eye.

Magnetic resonance imaging of spinal arteriovenous malformations

Magnetic resonance imaging (MRI) was performed on 12 patients with spinal arteriovenous malformations (AVM's). Six lesions were intramedullary, five were dural, and one was in a posterior extramedullary location. Serpentine filling defects similar to the classic myelographic findings were demonstrated within the high-signal cerebrospinal fluid on T2-weighted coronal scans. The intramedullary nidus was identified by MRI as an area of low-signal intensity within the cord in all six intramedullary AVM's. Neither the dural nor the posterior extramedullary lesions showed intramedullary components. It is concluded that MRI may noninvasively provide the initial diagnosis of a spinal AVM and distinguish intramedullary from dural and extramedullary lesions.

CT of cerebral abnormalities in precocious puberty

True precocious puberty occurs as a result of the premature release of luteinizing hormone-releasing hormone from the hypothalamus, which stimulates the secretion of the pituitary gonadotropins, which in turn stimulate the gonadal sex steroids. The differential diagnosis of true precocious puberty includes cerebral and idiopathic categories. This differentiation, which cannot be made endocrinologically due to similarities in pituitary gonadotropin and sex steroid levels, may be facilitated by high-resolution CT. A CT study of 90 children (73 girls and 17 boys) with true precocious puberty was performed at the NIH to detect cerebral causes of their precocious puberty. Thirty-four cerebral abnormalities were demonstrated in 32 children, 16 boys and 16 girls. These included hypothalamic hamartomas (17), hypothalamic astrocytoma (one), optic chiasm lesions (six), ventricular abnormalities (eight), arachnoid cyst (one), and teratoma (one). The CT appearance of these cerebral abnormalities is discussed and related to the endocrinologic findings and natural history of true precocious puberty. A practical neuroradiologic approach to the evaluation of children with precocious puberty is presented.

Pituitary adenomas in patients with Cushing disease: initial experience with Gd-DTPA-enhanced MR imaging

To assess the role of magnetic resonance imaging in the evaluation of adrenocorticotropic-hormone (ACTH)-producing pituitary adenomas, and the effect of intravenously administered gadolinium-diethylenetriaminepentaacetic acid (DTPA) on lesion/pituitary contrast, imaging was performed in 13 patients with clinical and chemical evidence of Cushing disease. Images were obtained at 0.5 T before and after the injection of Gd-DTPA (0.1 mmol/kg). Lesions were identified in eight of 12 precontrast and ten of 12 postcontrast studies. In these 12 patients adenomas were found at transsphenoidal surgery. The other patient, with normal images, was found to have an ectopic source of ACTH. Coronal images corresponded remarkably well with the neurosurgeon's intraoperative findings. Serial T1-weighted images disclosed early enhancement of the pituitary gland and delayed enhancement of the cystic adenomas. The discrepancy in times to peak enhancement accounted for improved lesion/pituitary contrast in some early images and for reversal or diminution of lesion/pituitary contrast in later images.

Magnetic resonance imaging versus computed tomography in the evaluation of soft tissue tumors of the extremities

Twenty patients with extremity soft tissue tumors were prospectively evaluated with magnetic resonance imaging (MRI) and computed tomography (CT) scans with subsequent anatomic correlation of surgical findings. MRI and CT had a similar percentage of accuracy in assessing tumor relationship with major neurovascular (80% and 70%, respectively) and skeletal (80% and 75%, respectively) structures. MRI was significantly better than CT in displaying contrast between tumor and muscle when using the T2 weighted spin echo (SE) (p2 less than 0.002) and inversion recovery (IR) (p2 less than 0.005) pulse sequences. MRI and CT were comparable in demonstrating contrast between tumor and fat. The contrast between tumor and vessel was better displayed by MRI compared with CT when using the T1 weighted SE (p2 less than 0.001) and T2 weighted SE (p2 less than 0.001) pulse sequences. T1 and T2 values were measured on fresh tumor and normal tissue samples and were used to predict relative contrast on different MRI pulse sequences using isosignal contour plots. MRI appears to offer several advantages over CT in the evaluation of extremity soft tissue tumors.

Gadolinium cryptelates as MR contrast agents

Gadolinium cryptelates are complexes of a lanthanide metal ion with amino acids of macrocyclic polyamines. These compounds are water soluble and possess reduced relaxation properties similar to Gd diethylene triamine pentaacetic acid (DTPA). Three Gd cryptelates (Gd NOTA, DOTA, TETA) were evaluated. Gadolinium DOTA is the most stable Gd complex with a dissociation constant of 10(-28) and appears to have a greater serum stability than Gd DTPA. Gadolinium NOTA and Gd TETA have lower dissociation constants than Gd DTPA at 10(-17) and 10(-19). Gadolinium DOTA has tissue distribution properties similar to Gd DTPA, is rapidly excreted by the kidneys, and provides a high degree of contrast enhancement on magnetic resonance (MR) images, both systemically and within the CNS. Hence, Gd DOTA is an alternative water-soluble MR contrast agent to Gd DTPA.