Effect of absorbable topical hemostatic agents on the relaxation time of blood: an in vitro study with implications for postoperative magnetic resonance imaging.

OBJECT: Absorbable topical hemostatic agents are commonly used in neurosurgery. In this study the authors examine the longitudinal relaxation time (T1) of blood in contact with these agents over time, measured in vitro, to determine if their presence could affect the interpretation of postoperative magnetic resonance (MR) images. METHODS: Coagulated and anticoagulated blood were used, both oxygenated and deoxygenated. The effects of a collagen-based agent (Collastat) and a cellulose-based agent (Surgicel) on the pH and T1 values of blood and on those of saline (used as a control) were investigated. The T1 was measured as a function of magnetic field strength and time by using a field-cycling relaxometer. This instrument measures 1/T1, the rate of T1, from which the T, value is computed. The T1 values of blood were compared with those of hemostat-induced blood clots and with those of both gray and white matter of the brain. Signal changes on T1-weighted MR images were predicted on the basis of altered T, values in vitro. Postoperative images were visually examined for the predicted changes. With the addition of Surgicel, blood had decreased pH and significantly shortened T1 at all fields, essentially within minutes, although it affected the T1 of saline only minimally. The effect of Surgicel increasingly shortened the T1 for 4 days in oxygenated blood. Collastat had no significant effect. The presence of some paramagnetic methemoglobin in Surgicel-induced clots was demonstrated using the relaxometer at a time when diamagnetic oxyhemoglobin would be present in naturally occurring blood clots. A bright signal that could mimic residual tumor on contrast-enhanced images was predicted and confirmed on postoperative T1-weighted MR images obtained in patients in whom Surgicel lined the tumor bed. It was not present in cases in which Surgicel was not used. CONCLUSIONS: Surgicel alters the appearance of early postoperative MR images. To avoid misinterpretation, clinicians should be aware of this phenomenon.

Reversal of radiographically impending stroke with multiple intraarterial papaverine infusions in severe diffuse cerebral vasospasm induced by subarachnoid hemorrhage.

BACKGROUND: Selective intraarterial infusion of papaverine is used in the treatment of symptomatic cerebral vasospasm induced by aneurysmal subarachnoid hemorrhage (SAH). Delays in instituting therapy for vasospasm can lead to irreversible cerebral infarction and a devastating outcome. Endovascular papaverine treatment of vasospasm in the presence of low-attenuation lesions on computed tomography (CT) is controversial, because of the fear of reperfusion hemorrhage in completed infarcts. METHOD: Two patients with aneurysmal SAH who subsequently developed severe diffuse vasospasm were identified. In both patients, large areas of low-attenuation change suggesting impending cerebral infarction were seen on CT scans. The patients received multiple infusions of intraarterial papaverine in an effort to treat vasospasm refractory to medical management. FINDINGS: After multiple intermittent administrations of papaverine, which initially appeared to increase the low-attenuation changes, there was dramatic reversal of the radiographic findings. There was also improvement in circulation time, transcranial Doppler velocities, and clinical outcome. INTERPRETATION: These findings suggest that in some patients, intraarterial infusions of papaverine initiated in the earliest stages of ischemia may exacerbate the radiographic appearance of low-attenuation changes, but may ultimately reverse the evolution of cerebral infarction.

Secretory and nonsecretory pituitary adenomas are distinguishable by 1/T1 magnetic relaxation rates at very low magnetic fields in vitro.

RATIONALE AND OBJECTIVES: The authors investigated whether hormonally active and inactive pituitary adenomas can be discriminated in vitro by magnetic resonance (MR) imaging-related data. METHODS: 1/T1 nuclear magnetic relaxation dispersion profiles were measured for 39 fresh surgical specimens of secreting and nonsecreting adenomas, classified using clinical criteria or preoperative serum hormone levels. Nonsecreting adenomas were subdivided into hormone-producing and nonhormone-producing by immunostains. At five fields (0.00024 to 1.2 tesla [T]), mean 1/T1 was analyzed for statistically significant differences among these three tumor categories. RESULTS: Mean 1/T1 was significantly higher (P < 0.02) for hormone-secreting than for nonsecreting adenomas at fields below 0.24 T; no significant difference existed at typical MR imaging fields (0.5 to 1.5 T). Mean 1/T1 for hormone-producing and nonhormone-producing, nonsecreting adenomas were not significantly different at any field. CONCLUSIONS: Because 1/T1 at low fields is related to 1/T2 at imaging fields, it may be possible to detect hormone secretion of pituitary adenomas noninvasively by MR imaging.

Calcification can shorten T2, but not T1, at magnetic resonance imaging fields. Results of a relaxometry study of calcified human meningiomas.

RATIONALE AND OBJECTIVES: Water content and water-proton relaxation rates are reported for fresh, histologically characterized, surgical specimens of calcified human intracranial meningiomas and compared with results for noncalcified meningiomas from an earlier study and with calcium hydroxyapatite (CaHA) suspensions to elucidate the influence of calcification on magnetic resonance imaging (MRI) signal intensity of calcified meningiomas. METHODS: The magnetic field dependence of 1/T1 of water protons (nuclear magnetic relaxation dispersion profile) and dry weights are reported for 38 calcified nonhemorrhagic and 3 hemorrhagic specimens of known histologic subtype, a subset of the 67 specimens measured earlier. Calcification was considered mild or heavy when the dry weight was within or above the range for noncalcified meningiomas. Preliminary 1/T1 profiles for pure CaHA and a single high-field 1/T2 value also are reported. RESULTS: The ranges of dry weights and of low-field 1/T1 values were twice as large for calcified as for noncalcified meningiomas. No correlation was found between low-field 1/T1 and either histologic subtype or dry weight. Mild calcification produced the highest low-field 1/T1 values; the most heavily calcified tumor had slightly increased low-field 1/T1. Calcium hydroxyapatite increases low-field 1/T1 significantly but not high-field 1/T1; high-field 1/T2 is large. For calcified hemorrhagic meningiomas, increases in both low-field and high-field 1/T1 were seen. CONCLUSION: For mild calcification, MRI signal voids result from an increased high-field 1/T2; for heavier calcification, reduced proton density (from excluded water) becomes of increasing importance. Cellular CaHA appears to brighten the signal in T1-weighted MRI in the presence of hemorrhage.

Relaxometry of noncalcified human meningiomas. Correlation with histology and solids content.

RATIONALE AND OBJECTIVES: Resected meningiomas were examined by relaxometry and light microscopy to evaluate the potential of magnetic resonance imaging (MRI) for identifying histologic subtypes and for discriminating among benign, radiation therapy-induced, and malignant meningiomas. METHODS: The magnetic field dependence of 1/T1 of water protons (nuclear magnetic relaxation dispersion [NMRD] profile) and the water content (dry weight) were measured for 67 specimens, and the data were compared with histology. Only noncalcified, nonhemorrhagic meningiomas are reported. RESULTS: No correlations were found between NMRD profiles, dry weight, and any histologic subtype, in contrast to an analogous study of astrocytomas. Rather, meningiomas have a broader variability of dry weight and 1/T1 than related parenchyma but a much narrower range than all grades of astrocytomas. The mean value of 1/T1, at all fields, is slightly higher in meningiomas--and the mean water content about the same--as adult cortical gray matter. CONCLUSION: Meningiomas are frequently isointense with cortex, and histologic subtypes cannot be differentiated at any magnetic field strength by MRI using only T1- or proton density-weighted MRI.

Correlation of intracranial pressure and transcranial Doppler resistive index after head trauma.

PURPOSE: To investigate the usefulness of transcranial Doppler ultrasonography in the evaluation of intracranial pressure changes after head injury. METHODS: Transcranial Doppler examinations and intracranial pressure measurements using intraparenchymal monitors were performed in 12 cases of closed head injury. Twenty-four sets of data, including the Glasgow Coma Scale, intracranial pressure, transcranial Doppler, and carbon dioxide pressure were compared. The side-to-side difference in the resistivity index was also assessed. RESULTS: There was a significant correlation between increased pressure values and resistivity index when comparing measurements from the same side. There was no correlation between carbon dioxide pressure and any transcranial Doppler parameter or intracranial pressure measurement. No significant correlation was found between the resistivity index and the Glasgow Coma Scale. End diastolic velocity was a stronger determinant of resistivity index than peak systolic velocity. CONCLUSION: The relationship of ipsilateral measurements of intracranial pressure to resistivity index is valid. The resistivity index must be analyzed within the context of the particular disease studied, especially with respect to the hemodynamic alterations. Initial findings suggest that intracranial pressure monitoring cannot be replaced by serial transcranial Doppler measurements in the treatment of the patient with acute head injury.

Variation of the magnetic relaxation rate 1/T1 of water protons with magnetic field strength (NMRD profile) of untreated, non-calcified, human astrocytomas: correlation with histology and solids content.

The magnetic relaxation rate 1/T1 of tissue water protons was measured over a wide range of magnetic field strengths (NMRD profile) for 92 fresh surgical specimens of astrocytomas to search for correlations of 1/T1 with tumor histology, as determined by light microscopy, and to assess the diagnostic potential of NMRD profiles for grading astrocytomas. A third goal was to elucidate the molecular determinants of 1/T1. Each specimen was histologically graded and inspected for evidence of mineral deposits (Ca, Fe); its dry weight was determined and expressed in % of original wet weight. To minimize variability not directly related to tumor grade, this initial report is limited to NMRD profiles of 47 non-calcified, non-hemorrhagic, untreated astrocytomas. For these, the mean value of 1/T1 at very low magnetic field strengths was found to increase with increasing grade of malignancy; no clear correlation could be demonstrated at high fields where most imaging is done. The spread of 1/T1 for different grades of malignancy is large, however, and the overlap significant, even at the lowest field, so that astrocytomas can not be graded by NMRD profiles alone. Average 1/T1 and average dry weight increase with grade of malignancy; but the variability of 1/T1 among specimens of the same dry weight is large, indicating that at least one other cellular parameter, not variable in normal tissue, influences 1/T1 strongly. We hypothesize that this parameter reflects changes at the molecular level in size distribution, mobility, or intermolecular interaction of cytoplasmic proteins. Which specific changes are induced by malignant transformation in astrocytomas remains to be investigated.

Cerebral blood flow velocity after head injury: transcranial Doppler evaluation. Work in progress.

To study blood flow velocity (BFV) changes, serial transcranial Doppler ultrasound (US) examinations of basal cerebral arteries were performed in 47 patients with head injury. Computed tomographic (CT) scans obtained at admission were analyzed for the presence of intracranial hemorrhages. Glasgow Coma Scale scores were obtained at admission in 46 patients. The prevalence of posttraumatic increased BFV was 77% (n = 36). Two groups of patients were identified according to the time of onset of increased BFV. They differed with respect to duration and severity of changes, Glasgow Coma Scale score, and evidence of intracranial hemorrhagic lesions. Low Glasgow Coma Scale scores were predictive of increased BFV within 72 hours after injury (P < .001). Patients with hemorrhages were significantly more prone to experience increased BFV within 72 hours (P < .05); 34% of patients who did not have hemorrhage, however, developed increased BFV. Increased BFV after head trauma is not uniformly found and cannot be explained by one pathologic mechanism.

Occipitocervical fusion for reduction of traumatic periodontoid hypertrophic cicatrix. Case report.

Periodontoid hypertrophic cicatrix resulting from trauma, as demonstrated by magnetic resonance (MR) imaging, is essentially the same as that seen in rheumatoid arthritis. Recent reports suggest that, in rheumatoid arthritis, occipitocervical fusion without transoral decompression of the pannus is adequate for resolution of this anterior lesion. A case of traumatic periodontoid cicatrix is presented in which posterior fusion resulted in reduction of the anterior mass lesion, clearly demonstrated by MR imaging. The etiology of periodontoid hypertrophic scarring, both traumatic and rheumatoid, is discussed in light of MR findings, and treatment implications are considered.

Postoperative evaluation of ascending aortic prosthetic conduits by magnetic resonance imaging.

Operative repair of ascending thoracic aortic dissection and aneurysm often involves the placement of prosthetic aortic conduits and stents with wrapping of the native aorta around the prosthetic device. Postoperative assessment has been clinical because of the absence of an adequate noninvasive imaging modality and a reluctance to perform invasive contrast aortography. Magnetic resonance imaging was performed on ten patients after operative placement of a prosthetic ascending aortic graft. The MR images were reviewed and a grading system was devised based on appearance of the operative site. An increase in MR signal was noted in some patients between the graft and wrapped native vessel. In 20 percent of patients vascular lumen compromise was noted. Magnetic resonance imaging offers a noninvasive technique to assess postoperative complications and offers a viable alternative to invasive contrast aortography.

Pitfalls in the diagnosis of erosive changes in expanding lesions of the pituitary fossa.

Tomographic findings were reviewed in 47 cases of transsphenoidal hypophysectomy for expanding intrasellar mass. Changes caused by factors other than the presence of a mass were classified into five groups. These were: (a) patterns of aeration of the sphenoid sinus, (b) sites of attachment of the sphenoid sinus septum, (c) thickening of the mucous membrane of the sphenoid sinus, (d) extensive thinning of the sellar cortex, and (e) sloping floors. These were the most common sites for causes of error in interpreting expanding lesions. An increased awareness of these pitfalls should decrease interpretive error.

Normal ocular circulation and the effect of arterial occlusive disorders.

Arterial occlusive disease, either primary or secondary, may not only affect the appearance of the ophthalmic artery, posterior ciliary arteries, and choroid crescent, but may be reflected in the prolongation of the circulation time to the choroid crescent. Choroid circulation time determined in 80 normal carotid angiograms showed that a value greater than 4.5 sec. for a population under 30 years of age, and greater than 5.6 sec. for a population 30 years of age and older, is prolonged. One should view these studies with suspicion and search for intra-orbital, intracranial, or extracranial arterial occlusive disease.

Galactorrhea and amenorrhea in a patient with an empty sella.

A report of a patient with amenorrhea and galactorrhea who was shown, by tomopneumoencephalogram, to have an empty sella is presented. Endocrinologic testing revealed only a blunted human growth hormone response to insulin-induced hypoglycemia and acyclicity of plasma gonadotropins. Thyroid testing, ACTH, and metopirone responses were normal. In addition, plasma prolactin levels were found to be within the normal range. Most significantly, after the pneumoencephalogram the patient's menses returned and have continued at regular monthly intervals for 6 months. During this time there has been a significant decrease in the galactorrhea. This is the first patient described with an empty sella and galactorrhea. The clinical and endocribologic aspects of the empty sella are discussed.