Paramesencephalic arachnoid cysts.

The term "paramesencephalic" is proposed to describe the location of a general class of arachnoid cysts observed in four patients. These cysts, which appear to arise within the subarachnoid space, are characterized by a lack of communication with the ventricular system. Usually, the arachnoid tissue is normal, and the cyst fluid resembles cerebrospinal fluid both macroscopically and microscopically. Hydrocephalus is variably accompanied by localizing signs. Problems may be encountered in the diagnosis of suprasellar (case 4), parapineal (case 3), incisural (case 1), and interpeduncular (cases 2 and 4) arachnoid cysts. Early surgical exploration is strongly recommended.

Magnetic resonance imaging of primary intracranial tumors: a review.

The experience in magnetic resonance (MR) imaging of primary intracranial neoplasia at University of California, San Francisco is reviewed. Seventy patients have been evaluated by MR and computerized tomography (CT). MR scans were performed using a multi-slice spin echo technique with a long pulse repetition time (TR = 2000 msec), and long echo sampling delay (TE = 56 msec). This method was most sensitive in differentiating normal gray and white matter and in detecting both cerebral edema and abnormal tissue with prolonged T2 characteristics. More sensitive to slight alterations in normal tissue, MR may detect a focal lesion in cases in which CT shows only mass effect. Moreover, MR may demonstrate more thoroughly the extent of tumor infiltration and broaden the characterization of abnormal tissue. Posterior fossa and brainstem anatomy are invariably better depicted by MR. The major limitations of MR include its inability to detect foci of tumor calcification, demonstrate the severity of bone destruction, or reliably distinguish tumor nidus from surrounding edema.

Optimal iodine concentration in digital subtraction arteriography.

The effects of two different concentrations of the contrast agent Hexabrix were evaluated in a total of 26 patients undergoing cerebral angiography and randomly assigned to two groups. Injection volume, rate, and iodine concentration were constant. Carotid digital exams using 8% and 12% Hexabrix in the same patient showed the higher concentration was preferred for vessels of all sizes. In comparing 12% and 16% concentrations of Hexabrix, there was again a preference for the higher concentration, although results were not statistically significant. Both 12% and 16% Hexabrix in carotid studies resulted in excellent quality exams. Vessel see-through ability was somewhat better with 12% Hexabrix. Subjective symptoms of all patients during the injection were minimal or absent. Hexabrix is theoretically more attractive than conventional agents in that optimal concentration for digital imaging is in a range which is iso-osmotic with serum.

Occipital lobe arteriovenous malformations. Clinical and radiologic features in 26 cases with comments on differentiation from migraine.

The differentiation of migraine headache, preceded by visual aura, from cerebral arteriovenous malformation (AVM) is often regarded as difficult. A study of 26 patients with occipital lobe AVM revealed two distinct syndromes in 18 patients--occipital epilepsy and occipital apoplexy. Occipital epilepsy is characterized either by elementary visual phenomena, such as brief flashes of light, or by dimming of a homonymous field. Occipital apoplexy results from hemorrhage and hematoma formation within the occipital lobe and is characterized by sudden headache and homonymous visual field loss. We conclude that patients harboring occipital AVMs may, indeed, have visual phenomena and headache that should not be confused with migraine because either a history of generalized seizure or bruits on examination will probably be present.

Intra-arterial embolization in the management of arteriovenous malformations.

Eighteen patients with arteriovenous malformations (AVM's) involving the extremities, pelvis, or head are reported and their treatment is discussed. Our experience has led us to the following conclusions: (1) careful selective angiography is mandatory to delineate the vascular anatomy, extent, and major afferent vessels supplying the AVM; (2) ligation of afferent vessels to an AVM never is indicated; (3) intra-arterial embolization (IAE) can be used prior to surgical removal of extensive but resectable AVM's; (4) IAE may be employed for symptom control of inoperable AVM's.

Localization studies in patients with persistent or recurrent hyperparathyroidism.

Preoperative localization studies are essential for patients who have undergone previous parathyroid operations. This is because the remaining parathyroid glands are more difficult to identify at operation because of increased scarring with loss of normal tissue planes and because the remaining abnormal parathyroid tissue is more likely to be situated in an ectopic position. This investigation concerns the accuracy of preoperative localization studies in 36 consecutive patients. All patients had symptoms and clinical and laboratory data diagnostic of primary (31 patients) or secondary (five patients) hyperparathyroidism. Ultrasonography was performed in all 36 patients; 18 (50%) were positive, 14 (39%) were negative, and four (11%) were false positive examinations. Eight of the negative study results occurred in patients with abnormal parathyroid glands situated in the mediastinum. Computerized tomography (CT) was performed in 25 patients. There was an equal number of positive (11; 44%) and negative (11; 44%) studies with three (12%) false positive test results. CT was helpful in identifying substernal lesions and other abnormal parathyroid glands situated in ectopic positions. Thallium chloride 201-technetium 99m pertechnetate scans were used in 22 patients. There was an equal number of positive (eight; 36%) and negative (eight; 36%) studies. Six patients (27%) had false positive scans. One or more of these noninvasive tests was positive in 27 of the 36 patients (75%). Highly selective venous catheterization for the measurement of immunoreactive parathyroid hormone concentrations localized the elusive parathyroid tumor in 12 of the 16 patients (75%) overall and in six of the nine patients (66%) whose tumors were not identified by other studies. One patient had both a false positive ultrasound and thallium chloride 201-technetium 99m pertechnetate scan. Preoperative localization studies were therefore very helpful for locating hyperfunctioning parathyroid glands in patients with recurrent or persistent hyperparathyroidism, and 75% of the tumors were identified by noninvasive studies. Seventy-five percent of the tumors not identified by noninvasive studies were localized by selective venous catheterization. Most tumors not identified by noninvasive studies were mediastinal or ectopic in position.

Localizing studies in patients with persistent or recurrent hyperparathyroidism.

Preoperative localizing studies are essential for patients with persistent or recurrent hyperparathyroidism requiring reoperation, because of loss of normal tissue planes and because the hyperfunctioning parathyroid tissue that remains is more likely to be situated in an ectopic position. The value of noninvasive and invasive localizing techniques was evaluated in 59 consecutive patients undergoing reoperation for persistent (40 patients) or recurrent (19 patients) hyperparathyroidism. Magnetic resonance imaging was performed in 17 patients; 11 results (65%) were positive, 3 (18%) were negative, and 3 (18%) were false-positive. Ultrasonography was performed in 52 patients; 29 (56%) were positive, 16 (31%) were negative, and 7 (13%) were false-positive. Computed tomography was performed on 41 patients; 19 (46%) were positive, 16 (39%) were negative, and 6 (15%) were false-positive. Thallium chloride 201-technetium 99m pertechnetate scans were used in 39 patients; 19 (49%) were positive, 11 (28%) were negative, and 9 (13%) were false-positive. One or more of these noninvasive tests was positive in 78% of the cases. Highly selective venous catheterization with measurement of immunoreactive parathyroid hormone concentration localized the abnormal parathyroid gland in 20 of 28 patients (71%) overall and in 8 of the 14 patients (57%) whose tumors were not identified by the noninvasive techniques. Since false-positive results were common, a combination of localizing studies was helpful in identifying the abnormal gland. Fifty-three of the 59 patients (90%) were successfully treated at the initial reoperation and three were successfully treated at a second reoperation. Advances in parathyroid localization have contributed to the improved surgical results in patients with persistent or recurrent hyperparathyroidism.

MR of aqueductal stenosis: evidence of a broad spectrum of tectal distortion.

The MR scans of 18 patients with nontumoral aqueductal stenosis and six patients with neoplastic stenosis of the aqueduct were reviewed in order to document and understand the variable appearance of the aqueduct and periaqueductal region on MR. The mesencephalic tectum is often distorted in patients with benign aqueductal narrowing. This distortion results in a number of different MR appearances ranging from an elongated and thin to a short and broad tectum. When compressed by a dilated suprapineal recess, the distorted tectum is sometimes difficult to differentiate from the bulbous enlargement caused by a tectal glioma. Patients in whom distortion of the tectum is the result of hydrocephalus and aqueductal stenosis should be recognized to avoid unnecessary diagnostic procedures and misdiagnosis.

Development of the pineal gland: measurement with MR.

PURPOSE: To use MR imaging in the analysis of the size of the normal pineal gland in infants, children, and adolescents. METHODS: We retrospectively analyzed the size of the pineal gland in 249 patients (129 male and 120 female) aged 2 weeks to 20 years old. The maximum length (L), height (H), and width (W) of the gland were determined from a combination of sagittal, coronal, and axial MR images obtained on a 1.5-T scanner. The volume was calculated by using the formula 1/2 x L x H x W. RESULTS: The size of the pineal gland was significantly smaller in patients younger than 2 years old than in older patients. The size of the pineal gland increased until 2 years of age and remained stationary between the ages of 2 and 20 years. We found a large variation in size among all age groups. No difference in size was noted between males and females. CONCLUSION: This study establishes norms for pineal gland size in infants younger than 2 years old and in children and adolescents 2 to 20 years old as detected with MR imaging. Knowledge of the size of the normal pineal gland is important in the detection of abnormalities of the pineal gland, particularly neoplasms.

Preoperative demonstration of postinflammatory syringomyelia.

Syringomyelia secondary to arachnoiditis is a rarely reported entity, which has not been described in the radiographic literature. A series of eight patients who had either postinfectious, posthemorrhagic, iatrogenic, or idiopathic arachnoiditis was examined recently with metrizamide computed tomography (CT). These patients presented with progressive neurologic deficits that could not be attributed to the level of arachnoid changes on myelography. On immediate and/or delayed CT scans, metrizamide accumulation within the central part of the cord was identified, both at and above the level of the arachnoiditis. In some patients, the cord diameter was normal. Syrinx cavities were demonstrated and shunted at surgery with subsequent partial relief or arrest of the symptoms. The mechanism of development of postinflammatory syringomyelia is discussed.

Cisternal enhancement after subarachnoid hemorrhage.

Abnormal computed tomographic enhancement in the basal cisterns and cortical sulci was observed in 21 of 42 patients after subarachnoid hemorrhage. The appearance is similar to that described in granulomatous infection and metastatic disease. The enhancement was associated with an increased incidence of hydrocephalus, but it did not correlate with clinical grade, arterial spasm, location of bleed, or temporal relation to bleed. Presumably, abnormal cisternal enhancement is due initially to increased vascular permeability and later to increased vascularity associated with arachnoiditis.

Traumatic aneurysms of cavernous internal carotid artery with secondary epistaxis.

The syndrome of delayed epistaxis and monocular blindness following nonpenetrating head injury is reviewed. Bleeding results from rupture of a traumatic cavernous internal carotid artery aneurysm into the sphenoid sinus. There were 96 patients with this syndrome found in the literature and another four are added in this report. In 73% of the patients, the cause of the epistaxis was not appreciated until 4 months after the initial episode. No antemortem diagnosis was made in 15% of the patients. More frequent use of carotid angiography in patients with posttraumatic mononuclear blindness and delayed epistaxis might help reduce the reported mortality of 30%.

CT and MR of angiomatous malformations of the choroid plexus in patients with Sturge-Weber disease.

Eight patients with Sturge-Weber disease were evaluated by CT (six patients), MR (one patient), or both (one patient). CT scans of five of seven patients showed enlargement and increased enhancement of the choroid plexus on the same side as the facial and intracranial lesions. MRI showed similar findings in both patients examined. This enlargement, seen in six of eight cases of Sturge-Weber disease, is compatible with the presence of angiomatous malformations of the choroid plexus. It appears to be a common finding in this disease.

Three-dimensional gradient-recalled MR imaging as a screening tool for the diagnosis of cervical radiculopathy.

The purpose of the study was to implement and assess a fast-screening, three-dimensional Fourier transformation (3DFT) MR sequence for the cervical spine. This sequence maintains adequate signal-to-noise and image contrast similar to gradient-recalled echo two-dimensional Fourier transformation (2DFT) imaging. Thirty patients with radiculopathy were examined with 3DFT gradient-recalled echo imaging. The data set consisted of 60 contiguous 1.5- to 2.0-mm-thick axial slices with a total coverage of 9 to 12 cm. In 10 patients, comparison was made with 4-mm-thick axial T1-weighted spin-echo 2DFT or gradient-recalled echo 2DFT studies. With the use of a volume acquisition, adequate signal-to-noise and image contrast similar to T2*-weighted gradient-recalled echo 2DFT acquisitions were obtainable. Coverage was improved despite the use of thinner sections without interslice gap. Thin-section 3DFT provided superior detail of acquired foraminal and spinal canal stenosis and disk morphology. Limitations included increased sensitivity to patient motion and "wraparound" artifact in the slice-select direction. Overall, diagnostic confidence was improved with 3DFT owing to the reduction of partial volume artifact. We have adopted this technique as the primary screening method for diagnosing cervical radiculopathy.

Gd-DTPA-enhanced MR imaging of pituitary adenomas.

Eleven previously nonoperated patients with suspected pituitary microadenomas were scanned on a 1.5-T GE system before and after administration of IV gadolinium-DTPA (0.1 mmol/kg). Six patients had Cushing disease, four had hyperprolactinemia, and one had acromegaly. Surgical confirmation was available in all cases, and these findings were correlated with results of CT and venous sampling, when available. The normal pituitary gland, infundibulum, and cavernous sinuses enhance immediately after the administration of gadolinium-DTPA, allowing contrast between the enhancing normal glandular tissue and low-intensity microadenomas. Contrast-enhanced MR detected a lesion not seen on the unenhanced images in two patients with Cushing disease and in one patient with hyperprolactinemia. Tumor delineation was improved with gadolinium administration in two additional cases. In six patients, administration of gadolinium did not significantly alter the precontrast interpretation. Adenomas were found at surgery in all 11 patients. The tumor was correctly localized on MR in four of the six patients with Cushing disease, resulting in an accuracy of 66.7%. In another patient, although a focal lesion was detected on MR, location of the adenoma at surgery was discrepant with the MR findings and was therefore considered a false-positive study. In the single false-negative examination, both pre- and postcontrast MR failed to detect a surgically confirmed microadenoma suspected on both contrast-enhanced CT and venous sampling. Correct localization of the adenoma was achieved in all of the five non-Cushing patients, yielding an accuracy of 100%. Immediate T1-weighted coronal scans were most useful in detecting intrasellar disease. Delayed scans obtained 30 min after injection did not improve the differentiation of pituitary gland from microadenoma.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

MRI of normal brain maturation.

The unprecedented gray/white differentiation obtained with magnetic resonance imaging (MRI) has created a unique opportunity to trace the normal process of myelination. Fifty-nine children referred for evaluation of a nonneurologic problem or a nonspecific neurologic complaint were studied with MRI using spin-echo technique. Children ranged in age from term (40 weeks intrauterine) to 16 years. Scans were reviewed for quantitative and qualitative changes with age. T1 and T2 relaxation times were measured for 13 regions of interest in 37 children. With increasing age a sharp decrease in both T1 and T2 values, most pronounced during the first year of life, was seen. The prolonged relaxation times in the newborn infant correspond to the known high water content of the neonatal brain; the subsequent decline corresponds to the decrease in water content and increase in myelination observed in autopsy studies of infants. Qualitative changes in the MRI appearance of the brain with age using a spin-echo sequence (2 sec repetition time) demonstrated that the process of myelination was most rapid during the first 2-3 years of life. Myelination appeared to occur earliest in the posterior fossa, with the middle cerebellar peduncle identifiable at only 3 months. By the age of 1 year, all major white matter tracts including the corpus callosum, subcortical white matter, and the internal capsule were well defined. However, due to subtle changes in appearance, the refined configuration of the adult brain was not attained until early adolescence.

Multiplanar metrizamide-enhanced CT imaging of the foramen magnum.

Definition of masses and malformations at the foramen magnum has been less than optimal with traditional radiographic techniques. The use of intrathecal metrizamide with computed tomographic (CT) scanning improves contrast resolution and facilitates detection of abnormalities that may not be apparent on Pantopaque cisternography, plain films, or conventional axial CT alone. Fifty patients with clinically suspected foramen-magnum lesions were evaluated with this technique. Forty were abnormal with the following findings: 14 cases of the Chiari malformation (five cases had associated syringomyelia), five meningiomas, three neuromas, a chondrosarcoma, a chordoma, and five cervical and three brainstem gliomas. Six cases of syringomyelia, a large posterior-fossa subarachnoid cyst, and an anomaly of the cisterna magna were also diagnosed. Sagittal and coronal images were beneficial in defining tonsillar position, configuration of the fourth ventricle, and the relations of mass lesions to the spinal canal and subarachnoid space. Metrizamide CT cisternography provides superior spatial and contrast resolution of lesions at the foramen magnum not obtainable with other radiographic techniques. Morbidity is minimal because of the low dose of metrizamide used. Multiplanar reformations are particularly helpful in assessing anatomic detail not readily recognized on axial scans alone.

Nuclear magnetic resonance imaging of syringomyelia.

Five patients with syringomyelia were examined with a 3.5 kG nuclear magnetic resonance (NMR) imager. Syrinx cavities were visualized in all five cases, and image quality compared favorably with metrizamide computed tomography (CT). Axial images were optimal for identifying syrinx cavities, and sagittal views were useful in providing an overview of cord morphology and in examining the craniocervical junction. Inversion-recovery images were less valuable than the spin-echo sequences. By varying spin-echo imaging parameters, tissue relaxation times could be determined and the fluid nature of the syrinx cavities confirmed. This limited study suggests that NMR may challenge the current role of CT in the diagnostic workup of syringomyelia.

Posterior pituitary ectopia: an MR feature of pituitary dwarfism.

Using high-field-strength, 1.5-T, high-resolution MR, we identified the following complex of neurohypophyseal abnormalities in each of five pituitary dwarfs: (1) severe hypoplasia or total absence of the infundibulum; (2) absence of the posterior pituitary bright spot in its normal location; and (3) a 3-8-mm tissue nodule at the median eminence exhibiting lipidlike signal on T1-weighted images. On the basis of its signal features and the clinical absence of diabetes insipidus in these patients, the median eminence nodule appears to represent an ectopic and functional posterior pituitary gland. We propose that this anatomic derangement is the end result of a localized defect of developmental origin, possibly ischemic in nature, and involving principally the infundibular stem. Thus, human growth hormone deficiency could result from perinatal disruption of the peri-infundibular hypophyseal portal system, which in turn impairs anterior pituitary function through deprivation of direct delivery of crucial hypothalamic-releasing factors. Finally, we suggest that the trophic influence of continued axonal neurosecretion at the median eminence engages proliferation of rest cell pituicytes; a process that induces formation of an ectopic and functional posterior pituitary gland, complete with its characteristic bright spot.