Diagnosis of symptomatic disc by magnetic resonance imaging: T2-weighted and gadolinium-DTPA-enhanced T1-weighted magnetic resonance imaging

Although radial tear of the annulus fibrosus can be detected on T2-weighted and Gd-DTPA-enhanced magnetic resonance (MR) images, the association between the annular tear on MR images and the symptomatic discs is unclear. The purpose of this study was to investigate the relationship between T2-weighted, gadolinium-DTPA-enhanced MR images and pain response through discography in patients with chronic low back pain. A total of 56 lumbar discs from 23 patients with chronic low back pain (13 to 47 years old) underwent MR imaging (T2-weighted, gadolinium-DTPA-enhanced MR images) followed by provocative discography. The sensitivity, specificity, positive predictive value, and negative predictive value of T2-weighted and gadolinium-DTPA-enhanced MR images in detecting the symptomatic discs were calculated. The sensitivity, specificity, positive predictive value, and negative predictive value of T2-weighted images in detecting the symptomatic disc were 94%, 71%, 59%, and 97%, respectively. The sensitivity, specificity, positive predictive value, and negative predictive value of gadolinium-DTPA-enhanced images were 71%, 75%, 56%, and 86%, respectively. The high sensitivity and the high negative predictive value of T2-weighted MR imaging in detecting the symptomatic disc indicated that MR imaging can be a useful screening tool in avoiding unnecessary discography in patients with chronic low back pain.     

磁共振观察宫颈癌放疗后盆部骨髓变化

目的分析宫颈癌放疗中与放疗后盆部骨髓MR改变。探讨MR成像对显示盆部骨髓损伤的临床价值。方法48例经病理证实的宫颈癌患者在放射治疗前及治疗中和治疗后不同时间段行盆腔的轴位SE T1WI，轴位及矢状位TSE T2WI，冠状位SPIR，以及Gd—DTPA增强后T1WI SE的轴位、冠状位、矢状位扫描。在MR图像上观察盆部骨髓在放疗前后的信号改变。结果骨髓信号最早出现改变是在外照射开始后第8天，患者受照剂量在12Gy时。放疗早期，骨髓在T1WI，T2WI及SPIR序列上信号升高，T1WI增强扫描见强化。放疗晚期，骨髓的T1WI，T2WI信号升高程度增加，SPIR序列出现信号降低，T1WI增强扫描，骨髓强化不明显。53％的患者在T1WI、T2WI上，18％的患者在SPIR序列上见照射野外骨髓信号有改变。结论宫颈癌外照射放疗可引起照射野内、外骨髓多种MR信号改变，并有一定规律性，对宫颈癌临床治疗有指导意义。     

Detection of hyperacute subarachnoid hemorrhage of the brain by using magnetic resonance imaging

OBJECT: The purpose of this study was to determine the diagnostic accuracy of high-field (1.5-tesla) magnetic resonance (MR) imaging in the assessment of hyperacute (< 12 hours after onset of symptoms) subarachnoid hemorrhage (SAH). METHODS: This investigation included 13 patients who were examined 2 to 12 hours posthemorrhage by using an MR imaging protocol consisting of T2-weighted and proton-density (PD)-weighted images, T1-weighted images, fast echoplanar-diffusion-weighted (EP-DW) images, and fluid-attenuated inversion-recovery (FLAIR) images. Subarachnoid hemorrhage had been diagnosed using computerized tomography (CT) scanning in all cases. In all 13 cases, SAH was reliably detected on both PD-weighted and FLAIR images. In contrast with FLAIR studies, the PD-weighted images were free of cerebrospinal fluid flow artifacts. The SAH was detected on T1-weighted images in only two cases and could not be detected on any T2-weighted or EP-DW images. CONCLUSIONS: Even hyperacute SAH can be diagnosed reliably from high-field MR images obtained using PD-weighted or FLAIR sequences. Use of these sequences in an emergency MR protocol may preclude the need for additional CT studies to rule out SAH.     

Transient osteoporosis of the hip. Magnetic resonance imaging

Magnetic resonance (MR) images of seven hips were reviewed in six patients with transient osteoporosis of the hip. The MR images of the affected joint showed increased joint fluid and diffuse signal abnormalities in the marrow of the femoral head, corresponding to a decreased signal intensity on T1-weighted images and an increased signal intensity on T2-weighted images. The MR images at the time of clinical improvement showed regression of the abnormalities. These MR abnormalities reflect the pathophysiology of this condition.     

Sequential magnetic resonance imaging following stereotactic radiofrequency ventralis lateralis thalamotomy

Serial postoperative magnetic resonance (MR) studies were obtained in 21 patients who underwent somatotopically placed stereotactic radiofrequency (rf) ventralis lateralis thalamotomy for the control of movement disorders. The MR studies were reviewed to determine the MR characteristics of early-phase (less than or equal to 7 days) and late-phase (8 days to 5 months) lesions. Surgery was performed for the control of parkinsonian tremor (14 cases), intention tremor (six cases), and essential tremor (one case). Single rf lesions were made with an electrode (1.6 mm in diameter, 3 mm in tip length) heated to 78 degrees C for 60 seconds. On MR images of the lesions, three distinct concentric zones were identified, described as follows (from the center outward). Zone 1 gives increased signal on long-relaxation time (TR) (T2-weighted) MR images in early- and late-phase lesions and decreased signal on short-TR (T1-weighted) MR images in early-phase lesions only. Zone 2 gives decreased signal on long-TR (T2-weighted) images in early- and late-phase lesions; it gives isointense signal on short-TR (T1-weighted) images in early-phase lesions only. Zone 3 gives increased signal on long-TR (T2-weighted) images in early-phase lesions only and decreased signal on short-TR (T1-weighted) MR images in early-phase lesions only. It is considered that in early-phase lesions, Zone 2, with a mean diameter of 7.3 mm on axial long-TR (T2-weighted) imaging, represents an area of hemorrhagic coagulation necrosis. In late-phase lesions, Zone 2, with a mean diameter of 5.0 mm on axial long-TR (T2-weighted) imaging, represents hemosiderin deposition. Zone 3 likely represents edema, and this zone disappears between the early and late periods. From regression analysis, lesion size began to stabilize at approximately 7 months with a mature lesion diameter of 3.3 mm. Long-term follow-up monitoring (median 16 months) showed good tremor control. Based on clinical and radiological findings, the authors conclude that forms of hemoglobin are suitable markers to assess the size of rf lesions. Serial MR imaging provides a noninvasive means of studying the evolution of rf thalamotomy lesions.     

Association between a black band on the inner membrane of a chronic subdural hematoma on T2*-weighted magnetic resonance images and enlargement of the hematoma

OBJECT: The cause and indication for enlargement of chronic subdural hematomas (CSDHs) have remained unresolved. The authors observed a black band on the inner membrane of a CSDH on T2*-weighted magnetic resonance (MR) images obtained in patients with symptoms. After surgical treatment, the band disappeared. The T2*-weighted sequence of MR imaging is an excellent diagnostic tool for detecting ferromagnetic substances, but it is rarely performed in cases of a CSDH. The authors speculate that the black band may be associated with the development of CSDH. METHODS: To investigate how the black band observed on T2*-weighted MR images contributes to the development of a CSDH, 59 lesions in 50 patients with CSDH (41 men and nine women, mean age 70 +/- 11 years [range 48-93 years]) were investigated prospectively. The incidence of black bands on the first T2*-weighted MR image obtained in patients with symptomatic CSDH was 97% (31 of 32 CSDHs), which was significantly higher than that associated with asymptomatic CSDH (11% [three of 27 CSDHs], p < 0.001). The black bands associated with symptomatic CSDH disappeared soon after surgical treatment in 31 CSDHs and became fainter in another. In two instances the CSDH recurred with reappearance of the band. Twenty-four of 27 asymptomatic CSDHs had no accompanying black band. Follow-up MR images demonstrated a later formation of bands in two of 24 asymptomatic CSDHs that enlarged to symptomatic size. Logistic regression analysis revealed that the heterogeneity and thickness of the CSDH on computerized tomography scans were independently and significantly associated with the black band. CONCLUSIONS: The dynamics of the black band may depend on the enlargement or shrinkage of the CSDH.     

High incidence of microbleeds in hemodialysis patients detected by T2*-weighted gradient-echo magnetic resonance imaging

The incidence and characteristics of microbleeds in hemodialysis (HD) patients were investigated to elucidate the clinical significance with T(2)(*)-weighted gradient-echo magnetic resonance (MR) imaging. The 57 patients with chronic renal failure maintained by HD had no previous history of stroke. The control group consisted of 53 patients without previous history of stroke or chronic renal failure. The incidence and the number of microbleeds were assessed in the HD and control groups. The findings of microbleeds with T(2)(*)-weighted gradient-echo MR imaging were compared with those of T(1)- and T(2)-weighted MR imaging in HD patients. The incidence of microbleeds was significantly greater in the HD patients compared with the control patients. T(2)(*)-weighted gradient-echo imaging revealed a total of 44 microbleeds in 11 HD patients. T(2)-weighted imaging demonstrated 13 of 44 microbleeds as hyperintensity, whereas T(1)-weighted imaging demonstrated 12 lesions as hypointensity. T(2)- and T(1)-weighted imagings did not demonstrate any findings in 31 and 32 lesions, respectively. T(2)(*)-weighted gradient-echo MR imaging is effective to detect microbleeds which may be a predictor of intracerebral hemorrhage in HD patients and should be included in the protocol for the study of cerebrovascular disease, because T(2)- and T(1)-weighted MR imaging recognizes microbleeds as lacunar infarction.     

Colloid (enterogenous) cyst in the frontal lobe

A 60-year-old man presented with a left frontal mass lesion incidentally detected at a health check without apparent symptoms. Computed tomography revealed the lesion as homogeneous high density and magnetic resonance (MR) imaging showed the lesion as hyperintense on T(1)-weighted images, isointense on T(2)-weighted images, and hypointense on diffusion-weighted images. T(1)-weighted MR images with gadolinium showed no enhancement of the mass lesion. Cerebral angiography revealed an avascular area around the left frontal lesion. Total removal of the lesion was achieved through a craniotomy without complications. Histological, immunohistochemical, and electron microscopy examinations established the definite diagnosis of colloid cyst.     

Computed tomography and magnetic resonance imaging of nonhemorrhagic, metastatic melanoma of the brain--case report.

Malignant melanoma frequently metastasizes to the central nervous system. Characteristic features of such lesions are increased density on computed tomography (CT) and shortening of the T1 and T2 on magnetic resonance (MR) imaging. Intratumoral hemorrhage, rather than melanin, is considered to be mainly responsible for these unique radiological features. The authors report a case involving a nonhemorrhagic, metastatic intracerebral melanoma. CT revealed a high-density mass, and MR imaging demonstrated a hyperintense mass both on T1- and T2-weighted images. These observations suggest that melanin is in fact a major determinant of the increased density on CT scans and the high signal intensity on T1-weighted MR images. On T2-weighted images, the paramagnetic effect appears to vary according to the melanin content.     

Rathke cleft cyst intracystic nodule: a characteristic magnetic resonance imaging finding

OBJECT: The fluid content of Rathke cleft cysts (RCCs) displays variable appearances on magnetic resonance (MR) images and can appear indistinguishable from other intrasellar or suprasellar cystic lesions. Intracystic nodules associated with individual RCCs have been noted, but to date their significance has not been fully explored. METHODS: The authors retrospectively reviewed MR imaging studies obtained in patients harboring intrasellar or suprasellar lesions that were consistent with RCCs to identify the presence and imaging characteristics of intracystic nodules. An intracystic nodule was present in nine (45%) of 20 patients with an RCC. All intracystic nodules were clearly visible and displayed a characteristic low signal intensity on T2-weighted MR images. The nodule was only visualized on T1-weighted images in four cases, in which it exhibited a consistent high signal intensity similar to that of the cyst fluid. The nodules did not enhance following the intravenous administration of a contrast agent. CONCLUSIONS: Although it is difficult to differentiate RCCs from other sellar cystic lesions because of the variable signal intensities displayed on MR images, the intensity of the intracystic nodule seems consistent on T1- and T2-weighted images, and the nodule is always clearly visible on T2-weighted images. With a nonenhancing cystic lesion that does not cause significant symptoms in the patient, the identification of an intracystic nodule with a characteristic signal intensity will aid in the diagnosis of RCC and the selection of conservative management.     

Atypical growth pattern of a meningioma in an adult

A 49-year-old woman presented with a rare atypical growth pattern of meningioma without evidence of dural attachment manifesting as chronic headache associated with transient paresthesia and left motor disorders. On admission, neurological examination showed no abnormalities. Magnetic resonance (MR) imaging revealed a right temporo-parieto-occipital lesion, which appeared to involve the subdural space and filling the cortical sulci. The lesion caused peritumoral white matter edema. The tumor appeared hypointense on T(1)-weighted and hyperintense on T(2)-weighted MR images, with homogeneous enhancement after contrast administration. A biopsy of the lesion was performed. Histological examination indicated that the lesion was a meningioma. Intraparenchymal meningiomas should be considered in the differential diagnosis of intraaxial lesions in patients of any age.     

High-resolution three-dimensional T2-weighted sequence for neuronavigation: a new setup and clinical trial

OBJECT: Conventional imaging for neuronavigation is performed using high-resolution computerized tomography (CT) scanning or a T1-weighted isovoxel magnetic resonance (MR) sequence. The extension of some lesions, however, is depicted much better on T2-weighted MR images. A possible fusion process used to match low-resolution T2-weighted MR image set with a referenced CT or T1-weighted data set leads to poor resolution in the three-dimensional (3D) reconstruction and decreases accuracy, which is unacceptable for neuronavigation. The object of this work was to develop a 3D T2-weighted isovoxel sequence (3D turbo-spin echo [TSE]) for image-guided neuronavigation of the whole brain and to evaluate its clinical application. METHODS: The authors performed a phantom study and a clinical trial on a newly developed T2-weighted isovoxel sequence, 3D TSE, for image-guided neuronavigation using a common 1.5-tesla MR imager (Siemens Sonata whole-body imager). The accuracy study and intraoperative image guidance were performed with the aid of the pointer-based Medtronic Stealth Station Treon. The 3D TSE data set was easily applied to the navigational setup and demonstrated a high registration accuracy during the experimental trial and during an initial prospective clinical trial in 25 patients. The sequence displayed common disposable skin fiducial markers and provided convincing delineation of lesions that appear hyperintense on T2-weighted images such as low-grade gliomas and cavernomas in its clinical application. CONCLUSIONS: Three-dimensional TSE imaging broadens the spectrum of navigational and intraoperative data sets, especially for lesions that appear hyperintense on T2-weighted images. The accuracy of its registration is very reliable and it enables high-resolution reconstruction in any orientation, maintaining the advantages of image-guided surgery.     

Prognostic relevance of the postoperative evolution of intramedullary spinal cord changes in signal intensity on magnetic resonance imaging after anterior decompression for cervical spondylotic myelopathy

OBJECT: Areas of intramedullary signal intensity changes (hypointensity on T1-weighted magnetic resonance [MR] images and hyperintensity on T2-weighted MR images) in patients with cervical spondylotic myelopathy (CSM) have been described by several investigators. The role of postoperative evolution of these alterations is still not well known. METHODS: A total of 47 patients underwent MR imaging before and at the end of the surgical procedure (intraoperative MR imaging [iMRI]) for cervical spine decompression and fusion using an anterior approach. Imaging was performed with a 1.5-tesla scanner integrated with the operative room (BrainSuite). Patients were followed clinically and evaluated using the Japanese Orthopaedic Association (JOA) and Nurick scales and also underwent MR imaging 3 and 6 months after surgery. RESULTS: Preoperative MR imaging showed an alteration (from the normal) of the intramedullary signal in 37 (78.7%) of 47 cases. In 23 cases, signal changes were altered on both T1- and T2-weighted images, and in 14 cases only on T2-weighted images. In 12 (52.2%) of the 23 cases, regression of hyperintensity on T2-weighted imaging was observed postoperatively. In 4 (17.4%) of these 23 cases, regression of hyperintensity was observed during the iMRI at the end of surgery. Residual compression on postoperative iMRI was not detected in any patients. A nonsignificant correlation was observed between postoperative expansion of the transverse diameter of the spinal cord at the level of maximal compression and the postoperative JOA score and Nurick grade. A statistically significant correlation was observed between the surgical result and the length of a patient's clinical history. A significant correlation was also observed according to the preoperative presence of intramedullary signal alteration. The best results were found in patients without spinal cord changes of signal, acceptable results were observed in the presence of changes on T2-weighted imaging only, and the worst results were observed in patients with spinal cord signal changes on both Tl- and T2-weighted imaging. Finally, a statistically significant correlation was observed between patients with postoperative spinal cord signal change regression and better outcomes. CONCLUSIONS: Intramedullary spinal cord changes in signal intensity in patients with CSM can be reversible (hyperintensity on T2-weighted imaging) or nonreversible (hypointensity on T1-weighted imaging). The regression of areas of hyperintensity on T2-weighted imaging is associated with a better prognosis, whereas the T1-weighted hypointensity is an expression of irreversible damage and, therefore, the worst prognosis. The preliminary experience with this patient series appears to exclude a relationship between the time of signal intensity recovery and outcome of CSM.     

Intracranial epidermoid tumor with changes in signal intensity on magnetic resonance imaging because of non-hemorrhagic pathology: case report

A 61-year-old woman presented an intracranial epidermoid tumor manifesting as dizziness and right facial hypesthesia. Magnetic resonance (MR) imaging revealed a well-defined lobulated mass in the right cerebellopontine angle as nearly isointense to the cerebrospinal fluid (CSF) on both T(1)- and T(2)-weighted images but inhomogeneously hyperintense on fluid-attenuated inversion recovery images. MR imaging performed 1 year later revealed that the tumor had significantly enlarged, and now appeared hyperintense to the CSF on T(1)- and T(2)-weighted images. The lesion was confirmed at surgery to be an epidermoid tumor filled with xanthochromic fluid. Histological examination found no evidence of hemorrhage in the resected tumor, so the changes in the MR imaging signal intensity were attributed to changes in the protein concentration of the intratumoral fluid, accumulation of debris, or some other non-hemorrhagic process.     

Multicentric intracranial fibrous xanthoma--case report.

Intracranial fibrous xanthoma is extremely rare; only 11 cases have been reported so far. The authors report a case of multicentric intracranial fibrous xanthoma. Precontrast computed tomographic (CT) scans revealed a left frontal subdural mass, which had previously been diagnosed as a chronic subdural hematoma at another hospital. However, operation disclosed no hematoma but a granulomatous tumor. The biopsied specimen was histologically diagnosed as fibrous xanthoma. Postoperative postcontrast CT scans showed intense homogeneous enhancement at the clival and the left frontal regions, both of which appeared as iso- to low-intensity areas on T1-weighted magnetic resonance (MR) images and as low-intensity areas on T2-weighted MR images. She gradually recovered by conservative treatment but suddenly died of cerebral infarction. Autopsy revealed fibrous xanthomas in the left frontal and the clival regions. This is the first report of the use of MR imaging for intracranial fibrous xanthoma, and its features differ from those of common intracranial parenchymal tumors, MR imaging can be helpful in the diagnosis of this tumor.     

Application of three-tesla magnetic resonance imaging for diagnosis and surgery of sellar lesions

OBJECT: The aim of this study was to determine the value of high-field magnetic resonance (MR) imaging for diagnosis and surgery of sellar lesions. METHODS: High-field MR images were obtained using a 3-tesla unit with emphasis on sellar and parasellar structures in 21 patients preoperatively to delineate endo-, supra-, and parasellar anatomical structures. Special attention was given to the medial border of the cavernous sinus and possible invasion of a sellar tumor therein, and to assessing the application of high-resolution images during intraoperative neuronavigation. The 3-tesla MR images were compared with the standard MR images already obtained and with intraoperative findings. Anatomical structures were studied in all 42 cavernous sinuses; in 32 of them comparisons with intraoperative findings were possible. The medial cavernous sinus border was rated intact in 53% on standard MR images, in 72% on 3-tesla MR images, and in 81% intraoperatively. With a positive correlation to surgical findings on 84% of 3-tesla MR images compared with 59% of standard MR images, a sensitivity of 83% compared with 67%, and a specificity of 84% compared with 58% (p = 0.016, McNemar test), 3-tesla MR imaging was superior for predicting tumor invasion through the medial cavernous sinus border. Although no difference was noted in delineation of the medial, superior, and inferior compartments, there was a better delineation of the lateral cavernous sinus compartment with 3-tesla MR imaging. This compartment was clearly visible on 40 sides (95%) on 3-tesla MR images compared with 34 sides (81%) on standard MR images. Identification of the cavernous sinus segments of the third, fourth, fifth (V1 and V2), and sixth cranial nerves was improved using high-resolution 3-tesla imaging compared with standard MR imaging. A mean of four cranial nerves was found as hypointense spots (range two-five spots) on 3-tesla MR imaging compared with a mean of three (range zero-four spots) on standard MR imaging. After addition of contrast agents, the anterior pituitary gland was found to be highly intense on 78% of T1-weighted three-dimensional magnetization-prepared rapid acquisition gradient-echo (MPRAGE) 3-tesla MR images compared with 73% of standard T1-weighted MR images. The optochiasmatic system displayed increased intensity on pre-contrast T1-weighted MPRAGE 3-tesla compared with standard T1-weighted MR images; it was hyperintense on 76% of 3-tesla compared with 15% of standard MR images, which was helpful for its delineation from suprasellar pituitary and tumor structures. Intraoperative navigation guided by fusion of 3-tesla MR images and computerized tomography (CT) scans was performed in seven patients. Whereas CT scanning was used during the transsphenoidal approach to depict the nasal bone structures, 3-tesla MR imaging was particularly useful for the visualization of parasellar tumor extension during microsurgical and/or endoscopic resection. CONCLUSIONS: Due to its higher resolution, 3-tesla MR imaging was found to be superior to standard MR imaging for the delineation of parasellar anatomy and tumor infiltration of the cavernous sinus, and this modality provided improved imaging for intraoperative navigation.     

Cavernous angioma of the internal acoustic meatus--case report

A 39-year-old female presented with an intrameatal cavernous angioma manifesting as hearing loss and tinnitus in the right ear which progressed over 8 months. Magnetic resonance (MR) images revealed an intrameatal lesion as ultra-high intensity, nearly as bright as cerebrospinal fluid, on the T2-weighted images, and isointensity on the T1-weighted images. Computed tomography (CT) showed the mass accompanied by stippled patterns of calcification. The patient underwent surgery under a diagnosis of calcified acoustic neurinoma. Histological studies were compatible with cavernous angioma. Intrameatal cavernous angioma is a rare disease which requires differential diagnosis from the more common neurinoma or meningioma in this location. Intrameatal lesion with ultra-high intensity on T2-weighted MR imaging and stippled patterns of calcification on CT is more likely to be cavernous angioma than acoustic neurinoma. These neuroimaging features are important information in deciding the treatment strategy.     

Neuroimaging of a wooden foreign body retained for 5 months in the temporalis muscle following penetrating trauma with a chopstick--case report

A 48-year-old female was stabbed by her husband with a chopstick made of wood in the left temporal region during a quarrel. She suffered laceration of the left temporal scalp. At initial examination, she concealed the assault with a chopstick. Radiography showed no abnormality, so the wound was sutured. One month after the injury, a painless subcutaneous mass appeared in the left temporal region which grew rapidly for 3 months. She was then admitted to our department. Computed tomography (CT) on admission showed a hyperdense area at the center of the mass. This area was hypointense on both T1- and T2-weighted magnetic resonance (MR) images. Temporalis muscle tumor with accompanying central necrosis, old hematoma, and inflammatory granuloma was considered. The mass was totally resected for cosmetic purposes and was found to be wooden foreign body granuloma. High density on CT and hypointensity on both T1- and T2-weighted MR images are characteristic of a chronically retained wooden foreign body in the living body and are useful for detecting wooden foreign bodies in the chronic granulomatous phase.     

Effect of intracranial pressure on the diameter of the optic nerve sheath

OBJECT: The subarachnoid space around the optic nerve in the orbit can be visualized using T2-weighted MR imaging with the fat-saturation pulse sequence. The optic nerve sheath (ONS) diameter can be estimated by measuring the outer diameter of the subarachnoid space. Dilated ONS is associated with idiopathic intracranial hypertension and hydrocephalus, and is believed to reflect increased intracranial pressure (ICP). The relationship between dilated ONS and ICP is unclear because of the difficulty in obtaining noninvasive measurements of ICP. The authors investigated the relationship between subdural pressure measured at the time of surgery and ONS diameter measured on MR images in patients with chronic subdural fluid collection. METHODS: Twelve patients underwent bur-hole craniostomy with continuous drainage for chronic subdural hematoma or hygroma in 2006. Orbital thin-slice fat-saturated MR images were obtained before and after surgery, and the ONS diameters were measured just behind the optic globe. Subdural pressure was measured using a manometer before opening of the dura mater. RESULTS: A significant correlation was found between the ONS diameter and the subdural pressure (correlation coefficient 0.879, p = 0.0036). The ONS diameter before surgery (6.1 +/- 0.7 mm) was significantly reduced after surgery (4.8 +/- 0.9 mm, p = 0.003; measurements are expressed as the mean +/- standard deviation). CONCLUSIONS: Increased ONS diameter measured on coronal orbital thin-slice fat-saturated T2-weighted MR images is a strong indicator of increased ICP, and helps to differentiate between passive subdural fluid collection due to brain atrophy and subdural hygroma with increased ICP.