Orbital lesions with low signal intensity on T2-weighted imaging.

The purpose of the present review is to discuss and display orbital lesions that demonstrate hypo-intense signal on T2-weighted images (T2WI). The physical basis for hypo-intense signal on T2WI produced by various substances is discussed. Orbital lesions that are hypo-intense on T2WI are subsequently reviewed, including a discussion on their composition as well as relevant clinical and imaging clues that may aid in their diagnosis.

Development and validation of a simple and practical method for differentiating MS from other neuroinflammatory disorders based on lesion distribution on brain MRI.

There is an unmet need to develop practical methods for differentiating multiple sclerosis (MS) from other neuroinflammatory disorders using standard brain MRI. To develop a practical approach for differentiating MS from neuromyelitis optica spectrum disorder (NMOSD) and MOG antibody-associated disorder (MOGAD) with brain MRI, we first identified lesion locations in the brain that are suggestive of MS-associated demyelination ("MS Lesion Checklist") and compared frequencies of brain lesions in the "MS Lesion Checklist" locations in a development sample of patients (n = 82) with clinically definite MS, NMOSD, and MOGAD. Patients with MS were more likely than patients with non-MS to have lesions in 3 locations only: anterior temporal horn (p < 0.0001), periventricular ("Dawson's finger") (p < 0.0001), and cerebellar hemisphere (p = 0.02). These three lesion locations were used as predictor variables in a multivariable regression model for discriminating MS from non-MS. The model had area under the curve (AUC) of 0.853 (95% confidence interval: 0.76-0.945), sensitivity of 87.1%, and specificity of 72.5%. We then used an independent validation sample with equal representation of MS and NMOSD/MOGAD cases (n = 97) to validate our prediction model. In the validation sample, the model was 76.3% accurate in discriminating MS from non-MS. Our simple method for predicting MS versus NMOSD/MOGAD only requires a neuroradiologist or clinician to ascertain the presence of lesions in three locations on conventional MRI sequences. It can therefore be readily applied in the real-world setting for training and clinical practice.

Development and Practical Implementation of a Deep Learning-Based Pipeline for Automated Pre- and Postoperative Glioma Segmentation.

BACKGROUND AND PURPOSE: Quantitative volumetric segmentation of gliomas has important implications for diagnosis, treatment, and prognosis. We present a deep-learning model that accommodates automated preoperative and postoperative glioma segmentation with a pipeline for clinical implementation. Developed and engineered in concert, the work seeks to accelerate clinical realization of such tools. MATERIALS AND METHODS: A deep learning model, autoencoder regularization-cascaded anisotropic, was developed, trained, and tested fusing key elements of autoencoder regularization with a cascaded anisotropic convolutional neural network. We constructed a dataset consisting of 437 cases with 40 cases reserved as a held-out test and the remainder split 80:20 for training and validation. We performed data augmentation and hyperparameter optimization and used a mean Dice score to evaluate against baseline models. To facilitate clinical adoption, we developed the model with an end-to-end pipeline including routing, preprocessing, and end-user interaction. RESULTS: The autoencoder regularization-cascaded anisotropic model achieved median and mean Dice scores of 0.88/0.83 (SD, 0.09), 0.89/0.84 (SD, 0.08), and 0.81/0.72 (SD, 0.1) for whole-tumor, tumor core/resection cavity, and enhancing tumor subregions, respectively, including both preoperative and postoperative follow-up cases. The overall total processing time per case was ∼10 minutes, including data routing (∼1 minute), preprocessing (∼6 minute), segmentation (∼1-2 minute), and postprocessing (∼1 minute). Implementation challenges were discussed. CONCLUSIONS: We show the feasibility and advantages of building a coordinated model with a clinical pipeline for the rapid and accurate deep learning segmentation of both preoperative and postoperative gliomas. The ability of the model to accommodate cases of postoperative glioma is clinically important for follow-up. An end-to-end approach, such as used here, may lead us toward successful clinical translation of tools for quantitative volume measures for glioma.

Differentiation of Jugular Foramen Paragangliomas versus Schwannomas Using Golden-Angle Radial Sparse Parallel Dynamic Contrast-Enhanced MRI.

BACKGROUND AND PURPOSE: Accurate differentiation of paragangliomas and schwannomas in the jugular foramen has important clinical implications because treatment strategies may vary but differentiation is not always straightforward with conventional imaging. Our aim was to evaluate the accuracy of both qualitative and quantitative metrics derived from dynamic contrast-enhanced MR imaging using golden-angle radial sparse parallel MR imaging to differentiate paragangliomas and schwannomas in the jugular foramen. MATERIALS AND METHODS: A retrospective study of imaging data was performed on patients (n = 30) undergoing MR imaging for jugular foramen masses with the golden-angle radial sparse parallel MR imaging technique. Imaging data were postprocessed to obtain time-intensity curves and quantitative parameters. Data were normalized to the dural venous sinus for relevant parameters and analyzed for statistical significance using a Student t test. A univariate logistic model was created with a binary output, paraganglioma or schwannoma, using a wash-in rate as a variable. Additionally, lesions were clustered on the basis of the wash-in rate and washout rate using a 3-nearest neighbors method. RESULTS: There were 22 paragangliomas and 8 schwannomas. All paragangliomas demonstrated a type 3 time-intensity curve, and all schwannomas demonstrated a type 1 time-intensity curve. There was a statistically significant difference between paragangliomas and schwannomas when comparing their values for area under the curve, peak enhancement, wash-in rate, and washout rate. A univariate logistic model with a binary output (paraganglioma or schwannoma) using wash-in rate as a variable was able to correctly predict all observed lesions (P < .001). All 30 lesions were classified correctly by using a 3-nearest neighbors method. CONCLUSIONS: Paragangliomas at the jugular foramen can be reliably differentiated from schwannomas using golden-angle radial sparse parallel MR imaging-dynamic contrast-enhanced imaging when imaging characteristics cannot suffice.

Dynamic Contrast-Enhanced MRI to Differentiate Parotid Neoplasms Using Golden-Angle Radial Sparse Parallel Imaging.

BACKGROUND AND PURPOSE: Conventional imaging frequently shows overlapping features between benign and malignant parotid neoplasms. We investigated dynamic contrast-enhanced MR imaging using golden-angle radial sparse parallel imaging in differentiating parotid neoplasms. MATERIALS AND METHODS: For this retrospective study, 41 consecutive parotid neoplasms were imaged with dynamic contrast-enhanced MR imaging with golden-angle radial sparse parallel imaging using 1-mm in-plane resolution. The temporal resolution was 3.4 seconds for 78.2 seconds and 8.8 seconds for the remaining acquisition. Three readers retrospectively and independently created and classified time-intensity curves as follows: 1) continuous wash-in; 2) rapid wash-in, subsequent plateau; and 3) rapid wash-in with washout. Additionally, time-intensity curve-derived semiquantitative metrics normalized to the ipsilateral common carotid artery were recorded. Diagnostic performance for the prediction of neoplasm type and malignancy was assessed. Subset multivariate analysis (n = 32) combined semiquantitative time-intensity curve metrics with ADC values. RESULTS: Independent time-intensity curve classification of the 41 neoplasms produced moderate-to-substantial interreader agreement (κ = 0.50-0.79). The time-intensity curve classification threshold of ≥2 predicted malignancy with a positive predictive value of 56.0%-66.7%, and a negative predictive value of 92.0%-100%. The time-intensity curve classification threshold of <2 predicted pleomorphic adenoma with a positive predictive value of 87.0%-95.0% and a negative predictive value of 76.0%-95.0%. For all readers, type 2 and 3 curves were associated with malignant neoplasms (P < .001), and type 1 curves, with pleomorphic adenomas (P < .001). Semiquantitative analysis for malignancy prediction yielded an area under the receiver operating characteristic curve of 0.85 (95% CI, 0.73-0.99). Combining time-to-maximum and ADC predicts pleomorphic adenoma better than either metric alone (P < .001). CONCLUSIONS: Golden-angle radial sparse parallel MR imaging allows high spatial and temporal resolution permeability characterization of parotid neoplasms, with a high negative predictive value for malignancy prediction. Combining time-to-maximum and ADC improves pleomorphic adenoma prediction compared with either metric alone.

Migrating subdural hematoma without subarachnoid hemorrhage in the case of a patient with a ruptured aneurysm in the intrasellar anterior communicating artery.

Acute spontaneous subdural hematoma without the presence of a subarachnoid hemorrhage as a result of a ruptured aneurysm is rare. We present the case of a patient with an aneurysm of the intrasellar anterior communicating artery that caused hemorrhage solely into the subdural space. The hemorrhage then migrated down the spinal canal. Our case is unique because all these 3 rare processes occurred in a single patient. Identification of the cause of this type of hemorrhage in a timely fashion is crucial to the management of such a patient.

Head and Neck MRI Findings in CHARGE Syndrome.

Coloboma of the eye, Heart defects, Atresia of the choanae, Retardation of growth and/or development, Genital and/or urinary abnormalities, and Ear abnormalities and deafness (CHARGE) syndrome is a disorder with multiple congenital anomalies seen on imaging. A retrospective review of 10 patients with CHARGE syndrome who underwent MR imaging of the brain as part of a preoperative evaluation for cochlear implantation was conducted. Structural abnormalities of the entire MR imaging of the head were evaluated, including the auditory system, olfactory system, face, skull base, and central nervous system. The most frequent MR imaging findings included dysplasias of the semicircular canals and hypoplasia of the frontal lobe olfactory sulci. Less frequent findings included cleft lip/palate and coloboma. Our study uncovered new findings of a J-shaped sella, dorsal angulation of the clivus, and absent/atrophic parotid glands, not previously described in patients with CHARGE. Our results emphasize the utility of MR imaging in the diagnosis and management of patients with CHARGE syndrome.

Role of High-Resolution Dynamic Contrast-Enhanced MRI with Golden-Angle Radial Sparse Parallel Reconstruction to Identify the Normal Pituitary Gland in Patients with Macroadenomas.

BACKGROUND AND PURPOSE: Preoperative localization of the pituitary gland with imaging in patients with macroadenomas has been inadequately explored. The pituitary gland enhancing more avidly than a macroadenoma has been described in the literature. Taking advantage of this differential enhancement pattern, our aim was to evaluate the role of high-resolution dynamic MR imaging with golden-angle radial sparse parallel reconstruction in localizing the pituitary gland in patients undergoing trans-sphenoidal resection of a macroadenoma. MATERIALS AND METHODS: A retrospective study was performed in 17 patients who underwent trans-sphenoidal surgery for pituitary macroadenoma. Radial volumetric interpolated brain examination sequences with golden-angle radial sparse parallel technique were obtained. Using an ROI-based method to obtain signal-time curves and permeability measures, 3 separate readers identified the normal pituitary gland distinct from the macroadenoma. The readers' localizations were then compared with the intraoperative location of the gland. Statistical analyses were performed to assess the interobserver agreement and correlation with operative findings. RESULTS: The normal pituitary gland was found to have steeper enhancement-time curves as well as higher peak enhancement values compared with the macroadenoma (P < .001). Interobserver agreement was almost perfect in all 3 planes (κ = 0.89). In the 14 cases in which the gland was clearly identified intraoperatively, the correlation between the readers' localization and the true location derived from surgery was also nearly perfect (κ = 0.95). CONCLUSIONS: This study confirms our ability to consistently and accurately identify the normal pituitary gland in patients with macroadenomas with the golden-angle radial sparse parallel technique with quantitative permeability measurements and enhancement-time curves.

New Clinically Feasible 3T MRI Protocol to Discriminate Internal Brain Stem Anatomy.

Two new 3T MR imaging contrast methods, track density imaging and echo modulation curve T2 mapping, were combined with simultaneous multisection acquisition to reveal exquisite anatomic detail at 7 canonical levels of the brain stem. Compared with conventional MR imaging contrasts, many individual brain stem tracts and nuclear groups were directly visualized for the first time at 3T. This new approach is clinically practical and feasible (total scan time = 20 minutes), allowing better brain stem anatomic localization and characterization.

High-Resolution DCE-MRI of the Pituitary Gland Using Radial k-Space Acquisition with Compressed Sensing Reconstruction.

BACKGROUND AND PURPOSE: The pituitary gland is located outside of the blood-brain barrier. Dynamic T1 weighted contrast enhanced sequence is considered to be the gold standard to evaluate this region. However, it does not allow assessment of intrinsic permeability properties of the gland. Our aim was to demonstrate the utility of radial volumetric interpolated brain examination with the golden-angle radial sparse parallel technique to evaluate permeability characteristics of the individual components (anterior and posterior gland and the median eminence) of the pituitary gland and areas of differential enhancement and to optimize the study acquisition time. MATERIALS AND METHODS: A retrospective study was performed in 52 patients (group 1, 25 patients with normal pituitary glands; and group 2, 27 patients with a known diagnosis of microadenoma). Radial volumetric interpolated brain examination sequences with golden-angle radial sparse parallel technique were evaluated with an ROI-based method to obtain signal-time curves and permeability measures of individual normal structures within the pituitary gland and areas of differential enhancement. Statistical analyses were performed to assess differences in the permeability parameters of these individual regions and optimize the study acquisition time. RESULTS: Signal-time curves from the posterior pituitary gland and median eminence demonstrated a faster wash-in and time of maximum enhancement with a lower peak of enhancement compared with the anterior pituitary gland (P < .005). Time-optimization analysis demonstrated that 120 seconds is ideal for dynamic pituitary gland evaluation. In the absence of a clinical history, differences in the signal-time curves allow easy distinction between a simple cyst and a microadenoma. CONCLUSIONS: This retrospective study confirms the ability of the golden-angle radial sparse parallel technique to evaluate the permeability characteristics of the pituitary gland and establishes 120 seconds as the ideal acquisition time for dynamic pituitary gland imaging.

Whole-Brain N-Acetylaspartate Concentration Is Preserved during Mild Hypercapnia Challenge.

BACKGROUND AND PURPOSE: Although NAA is often used as a marker of neuronal health and integrity in neurologic disorders, its normal response to physiologic challenge is not well-established and its changes are almost always attributed exclusively to brain pathology. The purpose of this study was to test the hypothesis that the neuronal cell marker NAA, often used to assess neuronal health and integrity in neurologic disorders, is not confounded by (possibly transient) physiologic changes. Therefore, its decline, when observed by using (1)H-MR spectroscopy, can almost always be attributed exclusively to brain pathology. MATERIALS AND METHODS: Twelve healthy young male adults underwent a transient hypercapnia challenge (breathing 5% CO2 air mixture), a potent vasodilator known to cause a substantial increase in CBF and venous oxygenation. We evaluated their whole-brain NAA by using nonlocalizing proton MR spectroscopy, venous oxygenation with T2-relaxation under spin-tagging MR imaging, CBF with pseudocontinuous arterial spin-labeling, and the cerebral metabolic rate of oxygen, during normocapnia (breathing room air) and hypercapnia. RESULTS: There was insignificant whole-brain NAA change (P = .88) from normocapnia to hypercapnia and back to normocapnia in this cohort, as opposed to highly significant increases: 28.0 ± 10.3% in venous oxygenation and 49.7 ± 16.6% in global CBF (P < 10(-4)); and a 6.4 ± 10.9% decrease in the global cerebral metabolic rate of oxygen (P = .04). CONCLUSIONS: Stable whole-brain NAA during normocapnia and hypercapnia, despite significant global CBF and cerebral metabolic rate of oxygen changes, supports the hypothesis that global NAA changes are insensitive to transient physiology. Therefore, when observed, they most likely reflect underlying pathology resulting from neuronal cell integrity/viability changes, instead of a response to physiologic changes.

Granulocytic sarcoma of the temporal bone.

We report an unusual case of granulocytic sarcoma involving the temporal bone. The occurrence of this tumor usually heralds acute myelogenous leukemia or the onset of the blastic phase of chronic myelogenous leukemia. Recognition of this rare entity is important, because early aggressive chemotherapy can cause regression of the tumor, as in our case, and thus improve patient longevity.

A retrospective analysis of spontaneous sphenoid sinus fistula: MR and CT findings.

BACKGROUND AND PURPOSE: The sphenoid sinus is rarely implicated as a site of spontaneous CSF fistula. We undertook this study to evaluate the potential etiopathogenesis of spontaneous CSF fistula involving the sphenoid sinus and to review the imaging findings. METHODS: We retrospectively reviewed the imaging findings of 145 cases of CSF fistula from our departmental archives (August 1995 through August 1998). Fifteen (10%) patients had CSF fistulas involving the sphenoid sinus. Eleven (7%) patients had spontaneous CSF fistulas, whereas in four patients, the CSF fistulas in the sphenoid sinus were related to trauma. Of the 11 patients, nine underwent only plain high-resolution CT and MR cisternography. One patient additionally underwent contrast-enhanced CT cisternography, and one other patient underwent MR cisternography only. For each patient, the CSF fistula site was surgically confirmed. The MR imaging technique included T1-weighted and fast spin-echo T2-weighted 3-mm-thick coronal sequences obtained with the patient in the supine position. The plain high-resolution CT study included 3-mm-thick, and sometimes 1- to 1.5-mm-thick, coronal sections obtained with the patient in the prone position. Similar sections were obtained after injecting nonionic contrast material intrathecally via lumbar puncture for the CT cisternographic study. We evaluated each of the 11 patients for the exact site of CSF leak in the sphenoid sinus. We also determined the presence of pneumatization of lateral recess of the sphenoid sinus, orientation of the lateral wall of the sphenoid sinus, presence of arachnoid pits, presence of brain tissue herniation, and presence of empty sella in each of these patients. RESULTS: The exact sites of the CSF fistulas were documented for all 11 patients by using plain high-resolution CT, MR cisternography, or CT cisternography. In nine (82%) patients, the sites of the CSF fistulas were at the junction of the anterior portion of the lateral wall of the sphenoid sinus and the floor of the middle cranial fossa. In the remaining two (18%) patients, the sites of the CSF fistulas were along the midportion of the lateral wall of the sphenoid sinus. Of these 11 patients, one had bilateral sites of the CSF fistula at the junction of the anterior portion of the lateral wall of the sphenoid sinus with the floor of the middle cranial fossa. In nine (82%) patients, the presence of brain tissue herniation was revealed, and this finding was best shown by MR cisternography. Ten (91%) patients had extensive pneumatization of the lateral recess of the sphenoid sinus, with an equal number having outward concave orientation of the inferior portion of the lateral wall of the sphenoid sinus. In seven (63%) patients, the presence of arachnoid pits, predominantly along the anteromedial aspect of the middle cranial fossa, was shown. In seven (63%) patients, empty sella was shown. For comparison, we reviewed the CT studies of the paranasal sinuses in 100 age-matched control subjects from a normal population. Twenty-three had extensive lateral pneumatization of the sphenoid sinus along with outward concavity of the inferior portion of the lateral wall. None of these 23 patients had arachnoid pits. CONCLUSION: The sphenoid sinus, when implicated as a site of spontaneous CSF leak, yields a multitude of imaging findings. These are extensive pneumatization of the lateral recess of the sphenoid sinus, outward concave orientation of the inferior portion of the lateral wall of the sphenoid sinus, arachnoid pits, and empty sella. Considering the normative data, we speculate that this constellation of findings could play a role in the etiopathogenesis of spontaneous sphenoid sinus fistulas. Our findings also show the efficacy of noninvasive imaging techniques, such as plain high-resolution CT and MR cisternography, in the evaluation of sphenoid sinus CSF leak. Our data also suggest that spontaneous sphenoid sinus CSF leak is not an uncommon occurrenc

The choline/creatine ratio in five benign neoplasms: comparison with squamous cell carcinoma by use of in vitro MR spectroscopy.

BACKGROUND AND PURPOSE: The choline (Cho)/creatine (Cr) ratio has been shown to be a reliable proton MR spectroscopy metabolic marker for differentiating squamous cell carcinoma (SCCA) from normal muscle in the upper aerodigestive tract. However, it is unclear whether the Cho/Cr ratio can be used to differentiate a malignant tumor from a benign neoplasm in the extracranial head and neck. Our purpose was to determine whether the Cho/Cr ratio can be used to differentiate benign from malignant tumors in this region. METHODS: In vitro one-dimensional proton MR spectroscopy (2,000/136,272 [TR/TE]) was performed at 11 T on tissue specimens obtained from glomus tumors (n = 3), inverting papilloma (n = 1), and schwannoma (n = 1). Cho/Cr area ratios were calculated and compared with similar, previously reported in vitro (11 T) findings and with samples of SCCA and normal muscle. RESULTS: The Cho/Cr ratio was elevated in relation to muscle in all benign tumors at TE = 136 (glomus tumors = 4.52, inverting papilloma = 3.85, schwannoma = 2.2) and at TE = 272 (glomus tumors = 8.01, inverting papilloma = 2.1, schwannoma = 4.28). The average Cho/Cr ratio for benign lesions was 3.92 (TE = 136) and 6.11 (TE = 272). The Cho/Cr ratio was significantly higher in benign tumors than in both SCCA and muscle. The average Cho/Cr ratio for muscle at TEs of 136 and 272 was 1.16 and 1.31, respectively, whereas for SCCA the average Cho/Cr ratio at TEs of 136 and 272 was 1.67 and 2.45, respectively. CONCLUSION: In our small group, the Cho/Cr ratio was significantly higher in benign tumors than in muscle and SCCA of the extracranial head and neck.

Distension technique to improve computed tomographic evaluation of oral cavity lesions.

BACKGROUND: The apposing mucosa of the oral cavity makes the computed tomographic identification of a clinically obvious mass difficult. Contrast distension techniques have been used in radiology to evaluate for presence of a "hidden" mass. OBJECTIVE: To illustrate the utility of distending the oral cavity with air, water, or contrast to display otherwise obscure oral cavity lesions. PATIENTS AND METHODS: In 3 normal subjects and 5 patients with biopsy-proved oral cavity lesions, serial contiguous 3-mm axial and coronal computed tomographic scans were obtained before and after distension of the oral cavity using intraoral air or water. Air distension was achieved by having the subjects perform a modified Valsalva maneuver during the scan acquisitions. Fluid distension was obtained using approximately 40 mL of water. RESULTS: In each case, the contrast successfully distended the oral cavity, separating the mucosal surfaces. Gingivobuccal lesions that were obscured by apposition of the lips and cheeks to the gums and teeth, or by apposition of the tongue to the inner margins of the gums and teeth, were clearly demonstrated. Lesions involving or extending into the retromolar trigone were also well demonstrated using this distension technique. CONCLUSIONS: Computed tomographic display of the anatomy and pathology of the oral cavity can be improved simply by distending the oral cavity using air or water as a contrast medium. This technique successfully shows lesions that are obscured by the apposing surfaces of the vestibule and the oral cavity proper, improving computed tomographic diagnosis.

Pneumocephalus secondary to colonic perforation by ventriculoperitoneal shunt catheter.

We present a case of colonic perforation as a complication arising from ventriculoperitoneal shunt catheter. A 58-year-old woman with a ventriculoperitoneal shunt catheter inserted for obstructive hydrocephalus was admitted to hospital with signs and symptoms of meningitis. CT showed an air-fluid level within both lateral ventricles, raising the possibility of colonic perforation since no other aetiology for the pneumocephalus could be found. The CT demonstration of the colonic perforation played a crucial role in patient management.

Imaging of congenital anomalies of the branchial apparatus.

One of the most challenging topics for radiologists is congenital anomalies arising from abnormal embryogenesis of the branchial apparatus. Defects of the branchial apparatus result in a spectrum of anomalies that includes fistulas, sinuses, cysts, temporal bone anomalies, craniofacial malformations, and systemic disorders. A better understanding of the various radiologic abnormalities is aided by an understanding of their embryonic origins. This article reviews the spectrum of abnormalities that are secondary to anomalous embryogenesis of the branchial arches.

Proton MR spectroscopy of the brain.

Magnetic resonance spectroscopy (MRS) has been shown to be an effective noninvasive diagnostic tool that can be used to monitor serially biochemical and metabolic changes in serial disease processes that affect the brain. MRS is now a clinical tool that is reimbursable. This article reviews MRS physics, techniques, pulse sequences, and the clinical applications of MRS.

Fungal diseases of the paranasal sinuses.

Fungal diseases of the paranasal sinuses can be categorized into the invasive and noninvasive varieties. The invasive form has been classified as acute fulminant fungal sinusitis, granulomatous invasive fungal sinusitis, and chronic invasive fungal sinusitis. The noninvasive form can be classified as the fungus ball and the allergic fungal sinusitis. The following review discusses the various types of fungal sinusitis with a special emphasis on the CT and MR imaging features.

Comparison of perfusion, diffusion, and MR spectroscopy between low-grade enhancing pilocytic astrocytomas and high-grade astrocytomas.

BACKGROUND AND PURPOSE: The differentiation of pilocytic astrocytomas and high-grade astrocytomas is sometimes difficult. There are limited comparisons in the literature of the advanced MR imaging findings of pilocytic astrocytomas versus high-grade astrocytomas. The purpose of this study was to assess the MR imaging, PWI, DWI, and MR spectroscopy characteristics of pilocytic astrocytomas compared with high-grade astrocytomas. MATERIALS AND METHODS: Sixteen patients with pilocytic astrocytomas and 22 patients with high-grade astrocytomas (8-66 years of age; mean, 36 ± 17 years) were evaluated by using a 1.5T MR imaging unit. MR imaging, PWI, DWI, and MR spectroscopy were used to determine the differences between pilocytic astrocytomas and high-grade astrocytomas. The sensitivity, specificity, and the area under the receiver operating characteristic curve of all analyzed parameters at respective cutoff values were determined. RESULTS: The relative cerebral blood volume values were significantly lower in pilocytic astrocytomas compared with the high-grade astrocytomas (1.4 ± 0.9 versus 3.3 ± 1.4; P = .0008). The ADC values were significantly higher in pilocytic astrocytomas compared with high-grade astrocytomas (1.5 × 10(-3) ± 0.4 versus 1.2 × 10(-3) ± 0.3; P = .01). The lipid-lactate in tumor/creatine in tumor ratios were significantly lower in pilocytic astrocytomas compared with high-grade astrocytomas (8.3 ± 11.2 versus 43.3 ± 59.2; P = .03). The threshold values ≥1.33 for relative cerebral blood volume provide sensitivity, specificity, positive predictive values, and negative predictive values of 100%, 67%, 87%, and 100%, respectively, for differentiating high-grade astrocytomas from pilocytic astrocytomas. The optimal threshold values were ≤1.60 for ADC, ≥7.06 for lipid-lactate in tumor/creatine in tumor, and ≥2.11 for lipid-lactate in tumor/lipid-lactate in normal contralateral tissue. CONCLUSIONS: Lower relative cerebral blood volume and higher ADC values favor a diagnosis of pilocytic astrocytoma, while higher lipid-lactate in tumor/creatine in tumor ratios plus necrosis favor a diagnosis of high-grade astrocytomas.