Anatomic Neuroimaging Characteristics of Posterior Fossa Type A Ependymoma Subgroups

BACKGROUND AND PURPOSE

Posterior fossa type A (PFA) ependymomas have 2 molecular subgroups (PFA-1 and PFA-2) and 9 subtypes. Gene expression profiling suggests that PFA-1 and PFA-2 tumors have distinct developmental origins at different rostrocaudal levels of the brainstem. We, therefore, tested the hypothesis that PFA-1 and PFA-2 ependymomas have different anatomic MR imaging characteristics at presentation.

MATERIALS AND METHODS

Two neuroradiologists reviewed the preoperative MR imaging examinations of 122 patients with PFA ependymomas and identified several anatomic characteristics, including extension through the fourth ventricular foramina and encasement of major arteries and tumor type (midfloor, roof, or lateral). Deoxyribonucleic acid methylation profiling assigned ependymomas to PFA-1 or PFA-2. Information on PFA subtype from an earlier study was also available for a subset of tumors. Associations between imaging variables and subgroup or subtype were evaluated.

RESULTS

No anatomic imaging variable was significantly associated with the PFA subgroup, but 5 PFA-2c subtype ependymomas in the cohort had a more circumscribed appearance and showed less tendency to extend through the fourth ventricular foramina or encase blood vessels, compared with other PFA subtypes.

CONCLUSIONS

PFA-1 and PFA-2 ependymomas did not have different anatomic MR imaging characteristics, and these results do not support the hypothesis that they have distinct anatomic origins. PFA-2c ependymomas appear to have a more anatomically circumscribed MR imaging appearance than the other PFA subtypes; however, this needs to be confirmed in a larger study.

The Impact of Persistent Leukoencephalopathy on Brain White Matter Microstructure in Long-Term Survivors of Acute Lymphoblastic Leukemia Treated with Chemotherapy Only

BACKGROUND AND PURPOSE

Survivors of acute lymphoblastic leukemia are at risk for neurocognitive deficits and leukoencephalopathy. We performed a longitudinal assessment of leukoencephalopathy and its associations with long-term brain microstructural white matter integrity and neurocognitive outcomes in survivors of childhood acute lymphoblastic leukemia treated on a modern chemotherapy-only protocol.

MATERIALS AND METHODS

One hundred seventy-three survivors of acute lymphoblastic leukemia (49% female), treated on a chemotherapy-only protocol, underwent brain MR imaging during active therapy and repeat imaging and neurocognitive testing at follow-up (median, 13.5 years of age; interquartile range, 10.7-17.6 years; median time since diagnosis, 7.5 years; interquartile range, 6.3-9.1 years). Persistence of leukoencephalopathy was examined in relation to demographic and treatment data and to brain DTI in major fiber tracts and neurocognitive testing at follow-up.

RESULTS

Leukoencephalopathy was found in 52 of 173 long-term survivors (30.0%) and persisted in 41 of 52 (78.8%) who developed it during therapy. DTI parameters were associated with leukoencephalopathy in multiple brain regions, including the corona radiata (fractional anisotropy, P = .001; mean diffusivity, P < .001), superior longitudinal fasciculi (fractional anisotropy, P = .02; mean diffusivity, P < .001), and superior fronto-occipital fasciculi (fractional anisotropy, P = .006; mean diffusivity, P < .001). Mean diffusivity was associated with neurocognitive impairment including in the genu of the corpus callosum (P = .04), corona radiata (P = .02), and superior fronto-occipital fasciculi (P = .02).

CONCLUSIONS

Leukoencephalopathy during active therapy and neurocognitive impairment at long-term follow-up are associated with microstructural white matter integrity. DTI may be more sensitive than standard MR imaging for detection of clinically consequential white matter abnormalities in childhood acute lymphoblastic leukemia survivors treated with chemotherapy and in children undergoing treatment.

Relative ADC and Location Differ between Posterior Fossa Pilocytic Astrocytomas with and without Gangliocytic Differentiation

BACKGROUND AND PURPOSE

Pilocytic astrocytomas, the most common posterior fossa tumors in children, are characterized by KIAA1549-BRAF fusions and shows excellent 5-year survival rates. Pilocytic astrocytoma with gangliocytic differentiation, a recently defined pilocytic astrocytoma variant that includes glial and neuronal elements similar to a ganglioglioma, may be distinguished from a classic ganglioglioma by molecular, radiologic, and histopathologic features. This study investigated whether imaging could distinguish posterior fossa pilocytic astrocytoma with and without gangliocytic differentiation.

MATERIALS AND METHODS

Preoperative MRIs (± CTs) of 41 children (age range, 7 months to 15 years; mean age, 7.3 ± 3.7 years; 58.5% male) with pilocytic astrocytoma with gangliocytic differentiation (n = 7) or pilocytic astrocytoma (n = 34) were evaluated; differences in tumor location, morphology, and minimum relative ADC between tumor types were compared (Wilcoxon rank sum test, Fisher exact test). Histopathology and BRAF fusion/mutation status were reviewed. Associations of progression-free survival with diagnosis, imaging features, and BRAF status were examined by Cox proportional hazards models.

RESULTS

Pilocytic astrocytoma with gangliocytic differentiation appeared similar to pilocytic astrocytoma but had lower minimum relative ADC (mean, 1.01 ± 0.17 compared with 2.01 ± 0.38 for pilocytic astrocytoma; P = .0005) and was more commonly located within midline structures (P = .0034). BRAF status was similar for both groups. Non-total resection (hazard ratio, 52.64; P = .0002), pilocytic astrocytoma with gangliocytic differentiation diagnosis (hazard ratio, 4.66; P = .0104), and midline involvement (hazard ratio, 3.32; P = .0433) were associated with shorter progression-free survival.

CONCLUSIONS

Minimum relative ADC and tumor location may be useful adjuncts to histopathology in differentiating pilocytic astrocytoma with gangliocytic differentiation from pilocytic astrocytoma. Shorter progression-free survival in pilocytic astrocytoma with gangliocytic differentiation is likely due to a propensity for involvement of midline structures and poor resectability.

MR Imaging Characteristics of Wingless-Type-Subgroup Pediatric Medulloblastoma

BACKGROUND AND PURPOSE

"Transcriptionally different" medulloblastoma groups are associated with specific signaling pathway abnormalities; hence, they may present with distinct imaging manifestations. In this study, we sought to describe the MR imaging features of wingless-type-subgroup medulloblastomas with embryologic correlations.

MATERIALS AND METHODS

Pre- and postoperative imaging studies of 16 patients with wingless-type-subgroup medulloblastoma were evaluated for tumor location, involvement of surrounding CSF spaces or parenchymal structures, conventional and DWI signal properties, and postsurgical damage patterns. Laterality scores were assigned to tumors at each step in the evaluation process. Continuous variables were summarized by using descriptive statistics. The Wilcoxon signed rank test was performed to compare laterality scores. To determine the interobserver variability, we computed the intraclass correlation and Cohen κ coefficients.

RESULTS

Wingless-type-subgroup medulloblastomas in our series were histopathologically "classic." Wingless-type-subgroup medulloblastomas occur in specific sites, with involvement of the foramen of Luschka (75%), the fourth ventricle (68.75%), the cisterna magna (31.25%), and the cerebellopontine angle cistern (18.75%). Laterality scores were low (<2) when preoperative primary and secondary anatomic features were evaluated separately, but they increased (>2) when all pre- and postoperative anatomic features were considered. Results were statistically shown to be reproducible (interclass correlation coefficient, 0.71-0.94; Cohen κ, 0.63-1.00). On the basis of anatomic lesion patterns, 4 location-based subtypes may be distinguished: 1) midline-intraventricular, 2) midline-extraventricular, 3) off-midline-intraventricular, and 4) off-midline-extraventricular, which represent a continuum.

CONCLUSIONS

Wingless-type-subgroup medulloblastomas are lateralized tumors arising from the brain stem and cerebellum around the foramen of Luschka. Our current understanding of their embryologic origins is in concordance with the spatial distribution of these tumors.

Comparison of the Outcomes and Recurrence with Three Surgical Techniques for Chronic Subdural Hematoma: Single, Double Burr Hole, and Double Burr Hole Drainage with Irrigation

Objective

Chronic subdural hematoma (CSDH), a disease commonly encountered by neurosurgeons, is treated by burr hole drainage (BHD). However, the optimal surgical technique among the three types of BHD has not been determined.

Methods

We conducted a retrospective study on BHD performed on 93 patients who were diagnosed with CSDH. The subjects were divided into three groups based on the surgical technique performed: single BHD without irrigation (Group A, n=31), double BHD without irrigation (Group B, n=32), and double BHD with irrigation (Group C, n=30). The clinical factors, radiological factors and recurrences were compared between the three groups. Moreover, independent factors affecting the recurrence were analyzed.

Results

The change in hematoma thickness was 29.77±7.94%, 49.73±12.87%, and 75.29±4.32% for Group A, B, and C, respectively, while the change in midline shift was 40.81±15.47%, 51.78±10.94%, and 56.16±16.16%, respectively. Thus, Group C showed the most effective for resolution of hematoma and midline shift (p<0.05). Group A, B, and C had 12 cases (38.7%), 8 cases (25.0%), and 3 cases (10.0%) of recurrences, respectively. Group C had a statistically significantly fewer recurrence rate than Group A (p<0.05). Double burr hole, irrigation, and coagulopathy were each identified as independent factors that reduce recurrence (p<0.05).

Conclusion

Among the three techniques, the double BHD with saline irrigation resulted in the fewest recurrences. It is probably the most effective technique for preventing the recurrence of CSDH.

Role of a Burr Hole and Calvarial Bone Marrow-Derived Stem Cells in the Ischemic Rat Brain: A Possible Mechanism for the Efficacy of Multiple Burr Hole Surgery in Moyamoya Disease

Objective

This study investigates the role of a burr hole and calvarial bone marrow-derived stem cells (BMSCs) in a transient ischemic brain injury model in the rat and postulates a possible mechanism for the efficacy of multiple cranial burr hole (MCBH) surgery in moyamoya disease (MMD).

Methods

Twenty Sprague-Dawley rats (250 g, male) were divided into four groups : normal control group (n=5), burr hole group (n=5), ischemia group (n=5), and ischemia+burr hole group (n=5). Focal ischemia was induced by the transient middle cerebral artery occlusion (MCAO). At one week after the ischemic injury, a 2 mm-sized cranial burr hole with small cortical incision was made on the ipsilateral (left) parietal area. Bromodeoxyuridine (BrdU, 50 mg/kg) was injected intraperitoneally, 2 times a day for 6 days after the burr hole trephination. At one week after the burr hole trephination, brains were harvested. Immunohistochemical stainings for BrdU, CD34, VEGF, and Doublecortin and Nestin were done.

Results

In the ischemia+burr hole group, BrdU (+), CD34 (+), and Doublecortin (+) cells were found in the cortical incision site below the burr hole. A number of cells with Nestin (+) or VEGF (+) were found in the cerebral parenchyma around the cortical incision site. In the other groups, BrdU (+), CD34 (+), Doublecortin (+), and Nestin (+) cells were not detected in the corresponding area. These findings suggest that BrdU (+) and CD34 (+) cells are bone marrow-derived stem cells, which may be derived from the calvarial bone marrow through the burr hole. The existence of CD34 (+) and VEGF (+) cells indicates increased angiogenesis, while the existence of Doublecortin (+), Nestin (+) cells indicates increased neurogenesis.

Conclusion

Based on these findings, the BMSCs through burr holes seem to play an important role for the therapeutic effect of the MCBH surgery in MMD.

Significance of C-reactive protein and transcranial Doppler in cerebral vasospasm following aneurysmal subarachnoid hemorrhage

Objective

Cerebral vasospasm is a common and potentially devastating complication of aneurysmal subarachnoid hemorrhage (aSAH). Inflammatory processes seem to play a major role in the pathogenesis of vasospasm. C-reactive protein (CRP) constitutes a highly sensitive inflammatory marker. Elevation of serum CRP levels has been demonstrated in patients with aSAH. The purpose of the current study was to evaluate the possible relationship between CRP levels in the serum and transcranial Doppler (TCD) and the development of vasospasm in patients with aSAH.

Methods

A total of 61 adult patients in whom aSAH was diagnosed were included in the study from November 2008 to May 2011. The patients' demographics, Hunt and Hess grade, Fisher grade, CT scans, digital subtraction angiography studies, and daily neurological examinations were recorded. Serial serum CRP measurements were obtained on days 1, 3, 5, 7, 9, 11 and 13 and TCD was measured on days 3, 5, 7, 9, 11 and 13. All patients underwent either surgical or endovascular treatment within 24 hours of their hemorrhagic attacks.

Results

Serum CRP levels peaked on the 3rd postoperative day. There were significant differences between the vasospasm group and the non-vasospasm group on the 1st, 3rd and 5th day. There were significant differences between the vasospasm group and the non-vasospasm group on the 3rd day in the mean middle cerebral artery velocities on TCD.

Conclusion

Patients with high levels of CRP on the 1st postoperative day and high velocity of mean TCD on the 3rd postoperative day may require closer observation to monitor for the development of vasospasm.

Primary malignant lymphoma of the cranial vault with extra- and intracranial extension

Bone involvement is a common finding in many types of lymphomas, particularly in advanced stages. However, cranial vault affliction has been regarded as an exceedingly rare presentation. Here, we report the case of a patient with cranial vault lymphoma who presented with a scalp mass. An 81-year-old woman presented with a gradually growing and non-painful frontal scalp mass that she noticed one month before admission. It was a flatly elevated, round mass measuring about 6×4×4 cm. Computed tomography and magnetic resonance imaging of the brain revealed a contrast-enhancing intracranial extradural mass at the counter-location of the scalp mass. The superior sagittal sinus was involved at the tumor site. Cerebral angiography showed that the tumor feeding vessels originated from the bilateral external carotid arteries. An operation was performed and the tumors were removed together with the involved bone. The pathologic diagnosis was malignant diffuse large B-cell type lymphoma. The patient was transferred to the Hemato-Oncology department for chemotherapy. Primary lymphoma of the cranial vault with scalp mass is very rare but it should be considered in the differential diagnosis of scalp masses. Although the results of reported cases are variable, the combination of surgery, radiation, and chemotherapy appears to offer favorable outcomes.

Cerebrospinal fluid pathways from cisterns to ventricles in N-butyl cyanoacrylate-induced hydrocephalic rats

OBJECT

Cerebrospinal fluid typically enters the subarachnoid space from the ventricles via the fourth ventricular foramina. However, there is clinical evidence that CSF also flows in the opposite direction. Ventricular reflux of CSF from a cistern is a well-known phenomenon in radioisotope studies in patients with normal-pressure hydrocephalus. Additionally, the presence of ventricular blood in acute subarachnoid hemorrhage is frequently observed. The goal of this investigation was to examine the potential CSF pathways from cisterns to ventricles. The authors examined pathways in rat models in which they occluded the fourth ventricular outlets and injected a tracer into the subarachnoid space.

METHODS

The model for acute obstructive hydrocephalus was induced using N-butyl cyanoacrylate (NBCA) in 10 Sprague-Dawley rats. After 3 days, cationized ferritin was infused into the lumbar subarachnoid space to highlight retrograde CSF flow pathways. The animals were sacrificed at 48 hours, and the brains were prepared. The CSF flow pathway was traced by staining the ferritin with ferrocyanide.

RESULTS

Ferritin was observed in the third ventricle in 7 of 8 rats with hydrocephalus and in the temporal horn of the lateral ventricles in 4 of 8 rats with hydrocephalus. There was no definite staining in the aqueduct, which suggests that the ventricular reflux originated from routes other than through the fourth ventricular outlets.

CONCLUSIONS

The interfaces between the quadrigeminal cistern and third ventricle and those between the ambient cistern and lateral ventricle appear to be potential sites of CSF reflux from cisterns to ventricles in obstructive hydrocephalus.

Clinical features of acute subdural hematomas caused by ruptured intracranial aneurysms

OBJECTIVE

Spontaneous acute subdural hematomas (aSDH) secondary to ruptured intracranial aneurysms are rarely reported. This report reviews the clinical features, diagnostic modalities, treatments, and outcomes of this unusual and often fatal condition.

METHODS

We performed a database search for all cases of intracranial aneurysms treated at our hospital between 2005 and 2010. Patients with ruptured intracranial aneurysms who presented with aSDH on initial computed tomography (CT) were selected for inclusion. The clinical conditions, radiologic findings, treatments, and outcomes were assessed.

RESULTS

A total of 551 patients were treated for ruptured intracranial aneurysms during the review period. We selected 23 patients (4.2%) who presented with spontaneous aSDH on initial CT. Ruptured aneurysms were detected on initial 3D-CT angiography in all cases. All ruptured aneurysms were located in the anterior portion of the circle of Willis. The World Federation of Neurosurgical Societies grade on admission was V in 17 cases (73.9%). Immediate decompressive craniotomy was performed 22 cases (95.7%). Obliteration of the ruptured aneurysm was achieved in all cases. The Glasgow outcome scales for the cases were good recovery in 5 cases (21.7%), moderate disability to vegetative in 7 cases (30.4%), and death in 11 cases (47.8%).

CONCLUSION

Spontaneous aSDH caused by a ruptured intracranial aneurysm is rare pattern of aneurysmal subarachnoid hemorrhage. For early detection of aneurysm, 3D-CT angiography is useful. Early decompression with obliteration of the aneurysm is recommended. Outcomes were correlated with the clinical grade and CT findings on admission.

Takayasu's arteritis complicated with subarachnoid hemorrhage and hematomyelia--case report

A 44-year-old woman presented with severe headache, drowsy mentality, and right hemiparesis. Brain computed tomography and magnetic resonance angiography revealed non-aneurysmal subarachnoid hemorrhage (SAH). Thoraco-abdominal and pelvic computed tomography angiography showed multiple steno-occlusive lesions involving the aorta and its large branches suggesting Takayasu's arteritis. Spine magnetic resonance imaging was taken because of prominent right hand muscle atrophy on the 14th hospital day, which showed subacute stage of hematomyelia in the cervical cord and conus medullaris. Aneurysmal or non-aneurysmal SAH is rare in patients with Takayasu's arteritis but SAH with coincidental hematomyelia is even more unusual. This case emphasizes the rarity of the coincidental spinal hematomyelia and its importance in the differential diagnosis.

A case of temporal intracerebral hemorrhage that presented with sudden bilateral hearing loss as the initial symptom

A 57-year-old man presented to the outpatient department with sudden bilateral hearing loss. The otological examination suggested bilateral severe sensorineural hearing loss. After several hours, the patient complained of a headache and became drowsy. The brain computed tomography showed a 3 × 4 cm intracerebral hemorrhage (ICH) of the left temporal lobe. Surgery was performed and 34 days after the procedure the patient was discharged from the hospital with severe bilateral sensorineural hearing loss (SNHL). Temporal lobe ICH should be considered in the differential diagnosis of patients with sudden bilateral hearing loss, regardless of the other neurological symptoms.

Capillary hemangioma of the thoracic spinal cord

Capillary hemangiomas are common soft tissue tumors on the skin or mucosa of the head and neck in the early childhood, but very rare in the neuraxis. A 47-year-old man presented with one month history of back pain on the lower thoracic area, radiating pain to both legs, and hypesthesia below T7 dermatome. Thoracic spine MRI showed 1×1.3×1.5 cm, well-defined intradural mass at T6-7 disc space level, which showed isointensity to spinal cord on T1, heterogeneous isointensity on T2-weighted images, and homogeneous strong enhancement. The patient underwent T6-7 total laminotomy, complete tumor removal and laminoplasty. Histologically, the mass showed a capsulated nodular lesion composed of capillary-sized vascular channels, which were tightly packed into nodules separated by fibrous septa. These features were consistent with capillary hemangioma.

Detection of traumatic cerebral microbleeds by susceptibility-weighted image of MRI

OBJECTIVE

Susceptibility-weighted image (SWI) is a sensitive magnetic resonance image (MRI) technique to detect cerebral microbleeds (MBLs), which would not be detected by conventional MRI. We performed SWI to detect MBLs and investigated its usefulness in the evaluation of mild traumatic brain injury (MTBI) patients.

METHODS

From December 2006 to June 2007, twenty-one MTBI patients without any parenchymal hemorrhage on conventional MRI were selected. Forty-two patients without trauma were selected for control group. According to the presence of MBLs, we divided the MTBI group into MBLs positive [SWI (+)] and negative [SWI (-)] group. Regional distribution of MBLs and clinical factors were compared between groups.

RESULTS

Fifty-one MBLs appeared in 16 patients of SWI (+) group and 16 MBLs in 10 patients of control group [control (+)], respectively. In SWI (+) group, MBLs were located more frequently in white matters than in deep nucleus different from the control (+) group (p < 0.05). Nine patients (56.3%) of SWI (+) group had various neurological deficits (disorientation in 4, visual field defect in 2, hearing difficulty in 2 and Parkinson syndrome in 1). Initial Glasgow Coma Scale (GCS)/mean Glasgow Outcome Scale (GOS) were 13.9 +/- 1.5 / 4.7 +/- 0.8 and 15.0 +/- 0.0 / 5.0 +/- 0.0 in SWI (+) and SWI (-) groups, respectively (p < 0.05).

CONCLUSION

Traumatic cerebral MBLs showed characteristic regional distribution, and seemed to have an importance on the initial neurological status and the prognosis. SWI is useful for detection of traumatic cerebral MBLs, and can provide etiologic evidences for some post-traumatic neurologic deficits which were unexplainable with conventional MRI.

Endovascular treatment for common iliac artery injury complicating lumbar disc surgery : limited usefulness of temporary balloon occlusion

Vascular injury during lumbar disc surgery is a rare but potentially life-threatening complication. It has been managed by open vascular surgical repair. With recent technologic advance, endovascular treatment became one of effective treatment modalities. We present a case of a 32-year-old woman who suffered with common iliac artery injury during lumbar disc surgery that was treated successfully by endovascular repair with temporary balloon occlusion and subsequent insertion of a covered stent. Temporary balloon occlusion for 1.5 hours could stop bleeding, but growing pseudoaneurysm was identified at the injury site during the following 13 days. It seems that the temporary balloon occlusion can stall bleeding from arterial injury for considerable time duration, but cannot be a single treatment modality and requires subsequent insertion of a covered stent.

Inflammatory pseudotumor in the lateral ventricle with repeated bleeding-case report-

Inflammatory pseudotumor is an uncommon lesion with unknown etiology characterized by sclerosing inflammation which clinically and radiographically mimics a neoplastic lesion. A 47-year-old man presented with sudden headache and dysarthria. Brain CT scan revealed a 2.6x2.2 cm sized, round, and hyperdense mass in the anterolateral wall of the left lateral ventricular trigone. On MR imaging studies, the mass showed low signal intensity in the wall of the trigone on T2-weighted image, central mixed (iso- and high-) signal intensity with peripheral low-signal intensity on T1-weighted image. Subtle staining of left choroid plexus with irregular shaped distal branch of anterior choroidal artery was found on the cerebral angiography. These findings suggested a small tumorous lesion originated from the left choroid plexus. During the hospital days, the mass manifested as repeated hemorrhages. The mass was successfully removed via left occipital transcortical approach. The histopathological report of the specimen was hemorrhage and fibrosis, with dense lymphoplasma cell infiltration, suggestive of an inflammatory pseudotumor.

The effect of barbiturate coma therapy for the patients with severe intracranial hypertension: a 10-year experience

OBJECTIVE

Barbiturate coma therapy (BCT) has been known to be an useful method to control increased intracranial pressure (IICP) refractory to medical and surgical treatments. We have used BCT for patients with severe IICP during the past 10 years, and analyzed our results with review of literatures.

METHODS

We analyzed 92 semicomatose or comatose patients with Glasgow coma scale (GCS) of 7 or less with severe IICP due to cerebral edema secondary to parenchymal damages irrespective of their causes. Forty patients who had received BCT with ICP monitoring from January 1997 to December 2006 were included in BCT group, and fifty-two patients who had been managed without BCT from January 1991 to December 1995 were divided into control group. We compared outcomes with Glasgow outcome scale (GOS) and survival rate between the two groups.

RESULTS

Good outcome (GOS=4 and 5) rates at 3-month after insult were 27.5% and 5.8% in BCT and control group, respectively (p<0.01). One-year survival rates were 35.9% and 12.5% in BCT and control group, respectively (p<0.01). In BCT group, the mean age of good outcome patients (37.1 +/- 14.9) was significantly lower than that of poor outcome patients (48.1 +/- 13.5) (p<0.05).

CONCLUSION

With our 10-year experience, we suggest that BCT is an effective treatment method for severe IICP patients for better survival and GOS, especially for younger patients.

Digital topological analysis of in vivo magnetic resonance microimages of trabecular bone reveals structural implications of osteoporosis

Osteoporosis is a disease characterized by bone volume loss and architectural deterioration. The majority of work aimed at evaluating the structural implications of the disease has been performed based on stereologic analysis of histomorphometric sections. Only recently noninvasive imaging methods have emerged that provide sufficient resolution to resolve individual trabeculae. In this article, we apply digital topological analysis (DTA) to magnetic resonance microimages (mu-MRI) of the radius obtained at 137 x 137 x 350 microm3 voxel size in a cohort of 79 women of widely varying bone mineral density (BMD) and vertebral deformity status. DTA is a new method that allows unambiguous determination of the three-dimensional (3D) topology of each voxel in a trabecular bone network. The analysis involves generation of a bone volume fraction map, which is subjected to subvoxel processing to alleviate partial volume blurring, followed by thresholding and skeletonization. The skeletonized images contain only surfaces, profiles, curves, and their mutual junctions as the remnants of trabecular plates and rods after skeletonization. DTA parameters were compared with integral BMD in the lumbar spine and femur as well as MR-derived bone volume fraction (BV/TV). Vertebral deformities were determined based on sagittal MRIs of the spine with a semiautomatic method and the number of deformities counted after threshold setting. DTA structural indices were found the strongest discriminators of subjects with deformities from those without deformities. Subjects with deformities (n = 29) had lower topological surface (SURF) density (p < 0.0005) and surface-to-curve ratio (SCR; a measure of the ratio of platelike to rodlike trabeculae; p < 0.0005) than those without. Profile interior (PI) density, a measure of intact trabecular rods, was also lower in the deformity group (p < 0.0001). These data provide the first in vivo evidence for the structural implications inherent in postmenopausal osteoporosis accompanying bone loss, that is, the conversion of trabecular plates to rods and disruption of rods due to repeated osteoclastic resorption.

Origin of a signal intensity loss artifact in fat-saturation MR imaging

Artifactual water signal intensity loss can be observed on fat-saturation magnetic resonance (MR) images of inhomogeneous regions such as the thorax. Magnetic effects of air inclusions on fat-saturation pulses were investigated as the possible origin of this artifact. Computer simulation results agreed well with observed production of water saturation by means of nominal fat suppression in MR imaging of phantoms and a representative clinical example.

Cross-sectional study of osteopenia with quantitative MR imaging and bone densitometry

PURPOSE

To evaluation the cancellous bone-induced intravoxel spin dephasing rate (R2') and its relationship to bone mineral density and marrow fat and to examine these parameters as predictors of vertebral fracture status.

MATERIALS AND METHODS

R2' and R2, the rate constants for reversible and irreversible spin dephasing, and marrow fat fraction were measured in the lumbar vertebrae and proximal femur. One hundred thirty-nine subjects (mean age, 62.4 years +/- 11.4 [SD]; 33 men, 106 women) had spinal dual-energy x-ray absorptiometric bone mineral density (BMD) T scores ranging from +3 to -5. R2', BMD, and bone marrow composition as determinants of vertebral fracture status were examined.

RESULTS

Strongest single predictors of fracture status for BMD and R2' were the Ward triangle (r(2) = 0.48) and trochanter (r(2) = 0.37), respectively. Combined, the two parameters and sites increased fracture prediction (r(2) = 0. 62), whereas the combination of multiple BMD sites did not. Multivariate regression involving marrow fat fraction further improved fracture status prediction. R2' was correlated with BMD at all sites, although slopes differed by a factor of up to 2.5, which reflected differences in trabecular orientation relative to the static field. R2, the true transverse relaxation rate, was negatively correlated with marrow fat fraction. A non-age-related increase in marrow fat fraction in osteoporosis parallels earlier findings in animal models.

CONCLUSION

Cancellous bone marrow R2' measured in the proximal femur provides information, which, with BMD, improves prediction of vertebral fracture status.

Topological analysis of trabecular bone MR images

Recently, imaging techniques have become available which permit nondestructive analysis of the three-dimensional (3-D) architecture of trabecular bone (TB), which forms a network of interconnected plates and rods. Most osteoporotic fractures occur at locations rich in TB, which has spurred the search for architectural parameters as determinants of bone strength. In this paper, we present a new approach to quantitative characterization of the 3-D microarchitecture of TB, based on digital topology. The method classifies each voxel of the 3-D structure based on the connectivity information of neighboring voxels. Following conversion of the 3-D digital image to a skeletonized surface representation containing only one-dimensional (1-D) and two-dimensional (2-D) structures, each voxel is classified as a curve, surface, or junction. The method has been validated by means of synthesized images and has subsequently been applied to TB images from the human wrist. The topological parameters were found to predict Young's modulus (YM) for uniaxial loading, specifically, the surface-to-curve ratio was found to be the single strongest predictor of YM (r2 = 0.69). Finally, the method has been applied to TB images from a group of patients showing very large variations in topological parameters that parallel much smaller changes in bone volume fraction (BVF).

The effects of N-methyl-N-nitrosourea and azoxymethane on focal cerebral infarction and the expression of p53, p21 proteins

If the activity of pro-apoptotic genes can be down-regulated by certain chemicals, cells may be protected from apoptosis. To test this hypothesis in a cerebral infarction model, we used N-methyl-N-nitrosourea (MNU) and azoxymethane (AOM), which were approved gene-modulating chemicals. A focal cerebral infarction was created by coagulation of the right middle cerebral artery and ipsilateral common carotid artery (CCA) and simultaneous transient occlusion of the contralateral CCA for 30 min in 25 adult Sprague-Dawley rats that were sacrificed 24 h later. In one group (n=7), MNU (5 mg/kg) was injected intravenously 30 min before initiation of ischemia. In another group (n=7), AOM (15 mg/kg) was administered intraperitoneally before 24 h of ischemia. The infarction volumes were checked and the brains were stained for p53 and p21 proteins. The width in micrometers of the peri-infarct area containing p53 or p21 protein-positive cells, and the number of p53 or p21 protein-positive cells (cells/HPF) were measured at an adjacent peri-infarct area. The AOM-treated group showed a significantly reduced infarction volume (by 42.5%, p<0.001), a significantly greater number of p53 positive cells (by 12.0%, p<0. 05), and a significantly wider p53 protein-positive area (by 15.6%, p<0.01) than the untreated group. AOM did not show any influence on the expression pattern of the p21 protein. MNU had no effect in the expression of p53 or p21 proteins. As a result, we concluded that AOM revealed a protective effect in ischemia by suppressing the pro-apoptotic activity of the p53 gene. Safer chemicals that can modulate apoptotic genes, if any, will provide a new therapeutic modality for cerebral infarction.

Relationship between cancellous bone induced magnetic field and ultrastructure in a rat ovariectomy model

The site-dependent variations in trabecular bone morphology were studied in the rat tibia by magnitude and phase difference three-dimensional nuclear magnetic resonance microscopy and image processing, and the implications of ovariectomy were evaluated. Specimens excised from the proximal tibial metaphysis in ovariectomized (n = 7) and intact control (n = 4) rats were imaged at 9.4T with their anatomic axes parallel to the direction of the magnetic field. An echo-offset 3D rapid spin-echo excitation pulse sequence was used to generate phase difference maps, from which the standard deviation of the phase difference, sigma(delta psi), was calculated. In addition, a fictitious rate constant, R2', was calculated from the slope of the exponential portion of the Fourier transform of the phase difference histogram. Trabecular bone volume fraction was also determined in the same volume of interest. The results show strong correlations between bone volume fraction and both sigma(delta psi) and R2', suggesting that these parameters could be useful for nondestructive assessment of trabecular bone volume.

Experimental evaluation of a surface charge method for computing the induced magnetic field in trabecular bone

The magnetic field induced in the pores of trabecular bone as a result of the susceptibility difference between bone and bone marrow was computed with the aid of magnetic surface charge models generated from images of trabecular bone specimens acquired at 78 and 63 microm resolution. The predicted field was compared with the values derived from 2D and 3D field maps obtained by echo-offset imaging techniques and excellent agreement was found between the two methods. Finally, from the slopes of regression between the experimental and computed fields, the absolute susceptibility of bone was nondestructively determined as -11.0 x 10(-6) (MKS), which is in close agreement with a reported value of -11.3 x 10(-6) obtained with powdered bone by means of a spectroscopic susceptibility matching technique (J. A. Hopkins and F. W. Wehrli, Magn. Reson. Med. 37, 494-500 (1997)).

Effect of prostaglandin and bisphosphonate on cancellous bone volume and structure in the ovariectomized rat studied by quantitative three-dimensional nuclear magnetic resonance microscopy

The purpose of this work was to evaluate the potential of nuclear magnetic resonance microscopy (NMRM) in conjunction with a processing technique to monitor the effect of preventive agents in an ovariectomized (OVX) rat. Twenty-five female Sprague-Dawley rats were OVX at 6 months of age (except for the intact control group), allowed to lose bone for 60 days, and then treated for 60 days. During treatment, animals were administered vehicle, prostaglandin E2 (PGE2; 6 mg/kg), or alendronate (3 microg/kg) subcutaneously once a day. Subsequently, tibiae were harvested and the marrow removed. NMRM was carried out at 9.4 T, with the specimens immersed in 1.2 mM diethylenetriaminepentaacetic acid-gadolinium salt (Gd-DTPA) aqueous solution. A three-dimensional (3D) partial flip-angle pulse sequence was used, providing a 1283 array of (46 microm)3 isotropic voxels. Fifty of the 128 axial images in the 3D data set comprising approximately 2.4 mm volume distal to the growth plate were processed from each specimen using a probability-based method for determining bone volume fraction (BVF), tubularity, contiguity, as well as the mean trabecular plate thickness and separation. PGE2 and alendronate altered BVF consistently at all tibial regions. The effect of alendronate was to keep BVF about midway between intact and OVX, whereas PGE2 returned BVF to intact levels. The other parameters showed similar responses to treatment. The strongest discriminator was trabecular BVF, which could obviously differentiate the groups. The study establishes NMRM as a nondestructive histomorphometric method for the quantitative evaluation of drug response in a rat ovariectomy model.

New architectural parameters derived from micro-MRI for the prediction of trabecular bone strength

This article reviews recent progress in magnetic resonance microimaging of cancellous bone in vitro and in vivo from the perspective of the authors' laboratory. It is shown that in particular in vivo the key technical prerequisites to satisfy are: (i) achieving sufficient signal-to-noise ratio (SNR) to allow for adequate spatial resolution; (ii) the image processing algorithms have to be robust enough to provide accurate structural information in the limited spatial resolution regime, i.e., in the presence of inevitable partial volume blurring and noise. The practical lower limit of voxel size in vivo was found to be about 6 x 10(-3) mm3 in the radius, and about 10(-4) mm3 for small specimens in vitro with state-of-the-art equipment and scan times of 10 and 30 minutes, resp., and SNR approximately 10. Finally, data are presented highlighting the potential of these methods for predicting the bone's elastic modulus in vitro and fracture risk in vivo.

Cancellous bone volume and structure in the forearm: noninvasive assessment with MR microimaging and image processing

PURPOSE

To develop and apply a method for the derivation of cancellous bone architectural parameters from in vivo magnetic resonance (MR) images of the distal radius and to evaluate these parameters as predictors of vertebral fracture status in osteopenia.

MATERIALS AND METHODS

MR images (137 x 137 x 500-micron3 voxel size) were acquired with a three-dimensional partial flip-angle spin-echo pulse sequence in the distal radius of 36 women. Subjects were classified as healthy or with osteoporosis on the basis of vertebral deformity and bone mineral density (BMD). Images rated as of adequate quality in 20 subjects were processed with a method that is applicable in the limited spatial resolution regime. The method relies on histogram deconvolution to obviate binary segmentation. Cancellous bone structure was treated as a quasi-regular lattice and analyzed with spatial autocorrelation, yielding parameters that quantify intertrabecular spacing, contiguity, and a measure of longitudinal alignment called tubularity.

RESULTS

Whereas neither BMD nor any of the structural parameters individually correlated significantly with vertebral deformity fraction, a simple function that involved tubularity and longitudinal spacing predicted deformity fraction well (r = .78, P < .005).

CONCLUSION

Histomorphometric parameters characterizing cancellous bone in the distal radius can be derived from in vivo MR microimages and are predictive of vertebral deformity.

Probability-based structural parameters from three-dimensional nuclear magnetic resonance images as predictors of trabecular bone strength

The mechanical competence of trabecular bone is a function of its apparent density and three-dimensional (3D) distribution. Three-dimensional structure is typically inferred from histomorphometry and stereology on a limited number of two-dimensional anatomic sections. In this work 3D nuclear magnetic resonance (NMR) images of anisotropic trabecular bone from the distal radius were analyzed in terms of a series of new structural parameters which are obtainable at relatively crude resolution, i.e., in the presence of substantial partial volume blurring. Unlike typical feature extraction techniques requiring image segmentation, the method relies on spatial autocorrelation analysis, which is based on the probability of finding bone at specified locations. The structural parameters were measured from high-resolution images (78x78x78 microm3 voxels) of 23 trabecular bone specimens from the distal radius. Maximum-likelihood bone volume fractions (BVF) were calculated for each voxel and a resolution achievable in vivo (156x156x391 microm3 voxels) was simulated by averaging BVF's from neighboring voxels. The parameters derived from the low-resolution images were found to account for 91% of the variation in Young's modulus. The results suggest that noninvasive assessment of the mechanical competence of trabecular bone in osteoporotic patients may be feasible.

A single-scan imaging technique for measurement of the relative concentrations of fat and water protons and their transverse relaxation times

A two-component chemical-shift-imaging technique is described from which fat and water images can be obtained in a single scan and in the presence of an inhomogeneous field. In addition, the method provides transverse relaxation rates R2 and R2' separately for each of the spectral components. The method is a combination and extension of the GESFIDE [gradient echo sampling of FID and echo, J. Ma and F. W. Wehrli, J. Magn. Reson. B 111, 61 (1996)] and the multipoint Dixon techniques. It is based on sampling the descending and ascending portions of a Hahn spin echo with a train of gradient echoes which are spaced at one-half of the chemical-shift modulation period. Processing of the complex echo data, involving an automated phase unwrapping algorithm, affords relative amplitudes and transverse relaxation rates of the two spectral components. An additional benefit of the method is its superior signal-to-noise ratio resulting from echo summation. Applications targeted and illustrated involve MRI osteodensitometry of trabecular bone in the presence of varying fractions of hematopoietic and fatty bone marrow.