CNS cavernous haemangioma: "popcorn" in the brain and spinal cord.

Cavernous haemangiomas (CH) are relatively uncommon non-shunting vascular malformations of the central nervous system and can present with seizures or with neurological deficits due to haemorrhage. Radiologists can often suggest the diagnosis of CH based on characteristic magnetic resonance imaging (MRI) features, thus avoiding further invasive procedures such as digital subtraction angiography or surgical biopsy. Although typical MRI appearance combined with the presence of multiple focal low signal lesions on T2*-weighted images or the presence of one or more developmental venous anomaly within the brain can improve the diagnostic confidence, serial imaging studies are often required if a solitary CH presents at a time when the imaging appearances had not yet matured to the typical "popcorn" appearance.

Primitive neuroectodermal tumour metastases mimicking neurofibromatosis type 2.

Bilateral vestibular schwannomas are the diagnostic features of neurofibromatosis type 2 (NF-2), and are the most common findings associated with the disorder. We report a three-year-old boy who presented with left facial nerve palsy and weight loss with bilateral large cerebellopontine (CP) angle masses that extended into the internal auditory canal on magnetic resonance imaging. The patient also had synchronous tumours in the lateral ventricle and intradural extramedullary spinal canal. The above findings were misinterpreted as NF-2 with bilateral vestibular schwannomas, ventricular meningioma and spinal schwannomas/meningiomas. However, histological examination of the spinal masses revealed a primitive neuroectodermal tumour. Although bilateral CP angle masses are characteristic of NF-2, the possibility of diffuse craniospinal malignancy should be considered in a very young child who presents with weight loss and extensive tumours.

Lipid Resonance on In Vivo Proton MR Spectroscopy: Value of Other Metabolites in Differential Diagnosis.

In vivo proton MR spectroscopy ((1)H-MRS) can non-invasively provide biochemical information at the same examination as conventional magnetic resonance imaging (MRI). Lipid resonance (0.9-1.5 ppm) is a marker of cell membrane breakdown and tissue necrosis, but its diagnostic significance has not been well described. We retrospectively analyzed spectra to study the different pathological conditions in patients with abnormal lipid resonance. All patients with neurological diseases showing lipid resonance on (1)H-MRS (1.5T) in a tertiary hospital over two years were retrospectively analyzed. (1)H-MRS was performed using the single voxel PRESS technique (TR/TE=3000/144 ms, eight excitations). Spectra were analysed for the presence of NAA (2.0 ppm), creatine (3.0 ppm), choline (3.2 ppm), acetate (1.92 ppm), succinate (2.4 ppm), cytosolic amino acids (0.9 ppm), lactate (1.3 ppm) and lipid (0.9-1.5 ppm) peaks. Ninety-two spectra from 69 patients (38 males, 31 females; aged 9 to 89 years) were analyzed. The final diagnosis was infective (n= 33), (tuberculoma n=17, pyogenic abscess n= 8, fungal abscess n= 3, sterile abscess n= 3, tubercular abscess n= 2), neoplastic (n= 21) (glial tumors n= 9, metastasis n= 8, lymphoma n= 4), and other (n= 15) abnormalities (subacute and chronic stroke n= 6, postictal edema n= 4, multiple sclerosis n= 2, Erdhiem Chester disease n= 2, Rosai Dorfmann disease n= 1). Succinate and acetate were detected only in pyogenic abscesses (2/4 cases), but amino acids were present in both pyogenic (4/8) and fungal (3/3) abscesses. Choline was seen not only in neoplasms (18) but also in tuberculomas (11/17), but was consistently absent in the abscesses. Lactate was present in glioblastoma (7/9), pyogenic (3/8) tubercular (2/2) and fungal (3/3) abscess. Isolated lipid resonance was found in Erdheim Chester disease (2/2) of the orbit, and lipid and choline was seen in Rosai Dorfmann's disease (1/1). Brain lesions containing lipid on (1)H-MRS could be differentiated by the presence of succinate and acetate in pyogenic abscess, and amino acids in pyogenic/fungal abscesses. Choline was seen in neoplasms and in tuberculomas, but not in the abscesses. Thus, the presence of a lipid peak, when combined with features on other MR pulse sequences and available clinical data can help arrive at a specific diagnosis. (1)H-MRS should not be interpreted in isolation: it should always be correlated with conventional imaging features, and performing (1)H-MRS in isolation remains an important pitfall.

Diffusion-weighted MR imaging: diagnosing atypical or malignant meningiomas and detecting tumor dedifferentiation.

BACKGROUND AND PURPOSE: Atypical and malignant meningiomas are uncommon tumors with aggressive behavior and higher mortality, morbidity, and recurrence compared with benign tumors. We investigated the utility of diffusion-weighted (DW) MR imaging to differentiate atypical/malignant from benign meningiomas and to detect histologic dedifferentiation to higher tumor grade. MATERIALS AND METHODS: We retrospectively compared conventional and DW MR images (b-value 1000 s/mm(2)) acquired on a 1.5T clinical scanner between 25 atypical/malignant and 23 benign meningiomas. The optimal cutoff for the absolute apparent diffusion coefficient (ADC) and normalized ADC (NADC) ratio to differentiate between the groups was determined by using receiver operating characteristic (ROC) analysis. RESULTS: Irregular tumor margins, peritumoral edema, and adjacent bone destruction occurred significantly more often in atypical/malignant than in benign meningiomas. The mean ADC of atypical/malignant meningiomas (0.66 +/- 0.13 x 10(-3) mm(2)/s) was significantly lower compared with benign meningiomas (0.88 +/- 0.08 x 10(-3) mm(2)/s; P < .0001). Mean NADC ratio in the atypical/malignant group (0.91 +/- 0.18) was also significantly lower than the benign group (1.28 +/- 0.11; P < .0001), without overlap between groups. ROC analysis showed that ADC and NADC thresholds of 0.80 x 10(-3) mm(2)/s and 0.99, respectively, had the best accuracy: at the NADC threshold of 0.99, the sensitivity and specificity were 96% and 100%, respectively. Two patients had isointense benign tumors on initial DW MR imaging, and these became hyperintense with the decrease in ADC and NADC below these thresholds when they progressed to atypical and malignant meningiomas on recurrence. CONCLUSIONS: ADC and NADC ratios in atypical/malignant meningiomas are significantly lower than in benign tumors. Decrease in ADC and NADC on follow-up imaging may suggest dedifferentiation to higher tumor grade.

Delineation and segmentation of cerebral tumors by mapping blood-brain barrier disruption with dynamic contrast-enhanced CT and tracer kinetics modeling-a feasibility study.

Dynamic contrast-enhanced (DCE) imaging is a promising approach for in vivo assessment of tissue microcirculation. Twenty patients with clinical and routine computed tomography (CT) evidence of intracerebral neoplasm were examined with DCE-CT imaging. Using a distributed-parameter model for tracer kinetics modeling of DCE-CT data, voxel-level maps of cerebral blood flow (F), intravascular blood volume (vi) and intravascular mean transit time (t1) were generated. Permeability-surface area product (PS), extravascular extracellular blood volume (ve) and extraction ratio (E) maps were also calculated to reveal pathologic locations of tracer extravasation, which are indicative of disruptions in the blood-brain barrier (BBB). All maps were visually assessed for quality of tumor delineation and measurement of tumor extent by two radiologists. Kappa (kappa) coefficients and their 95% confidence intervals (CI) were calculated to determine the interobserver agreement for each DCE-CT map. There was a substantial agreement for the tumor delineation quality in the F, ve and t1 maps. The agreement for the quality of the tumor delineation was excellent for the vi, PS and E maps. Concerning the measurement of tumor extent, excellent and nearly excellent agreement was achieved only for E and PS maps, respectively. According to these results, we performed a segmentation of the cerebral tumors on the base of the E maps. The interobserver agreement for the tumor extent quantification based on manual segmentation of tumor in the E maps vs. the computer-assisted segmentation was excellent (kappa = 0.96, CI: 0.93-0.99). The interobserver agreement for the tumor extent quantification based on computer segmentation in the mean images and the E maps was substantial (kappa = 0.52, CI: 0.42-0.59). This study illustrates the diagnostic usefulness of parametric maps associated with BBB disruption on a physiology-based approach and highlights the feasibility for automatic segmentation of cerebral tumors.

MR regional perfusion imaging: visualizing functional collateral circulation.

SUMMARY: We applied regional perfusion imaging (RPI), a new arterial spin-labeling MR imaging method that selectively studies regions of the brain perfused by individual carotid and basilar arteries. In a patient with cerebrovascular disease, RPI showed cerebral tissue perfused by pial collateral vessels, thereby demonstrating the relationship between anatomic and functional information, which was lacking in conventional x-ray angiography. RPI may be useful to study functional collateral circulation and hence guide therapy in ischemic disease.

Neuroradiology imaging database: using picture archive and communication systems for brain tumour research.

INTRODUCTION: Disease registries and databases form an important component of research in clinical medicine, and can be useful to support retrospective studies and prospective clinical trials. However, analysis of radiological imaging databases has not been explored: imaging and clinical data often exist as separate silos of information, even in modern digital-enabled hospitals in Singapore. We describe a computerised method for creating a radiological research database using data from the picture archive and communication system (PACS) and hospital information system (HIS). METHODS: Using a relational database and Java programming language, we created the neuroradiology imaging database (NRID). A web-interface for keyword searches were tested with the clinical data from PACS of a tertiary referral hospital for neurological diseases. Keyword and wildcard searches were conducted for various brain neoplasms and compared to HIS discharge diagnosis. RESULTS: The NRID was deployed successfully and keyword search could be completed in real time. Lists of patients with meningioma, oligodendroglial tumour, neurocytomas, cerebral abscess, and neurocysticercosis could be exported and compared with the HIS discharge diagnosis. Patients with neurological diseases could be obtained by manually combining lists. CONCLUSION: An imaging database can be created using clinical PACS data, which can enable keyword search functions to support brain tumour research. Radiological databases can help support clinical research, but further work needs to be done in order to take full advantage of the potential of digital health information.

Paediatric PNET: pre-surgical MRI features.

AIM: To describe the preoperative magnetic resonance imaging (MRI) characteristics of primitive neuroectodermal tumours (PNETs), in particular the diffusion-weighted imaging (DWI), MR spectroscopy (MRS) features and cerebrospinal fluid (CSF) tumour dissemination. MATERIAL AND METHODS: Twelve patients with PNETs were reviewed: nine with medulloblastoma and three with supratentorial PNETs (SPNETs). The MRI examination included contrast-enhanced intracranial and spinal MRI, and in some patients, gradient recalled echo, fluid-attenuated inversion recovery (FLAIR), DWI, and MRS. RESULTS: All PNETs were either hypointense or isointense on T1-weighted images. Ten of the 12 tumours were either isointense or hypointense on T2-weighted images, and 11 were isointense on FLAIR images. Patients with SPNETs had large, vascular and haemorrhagic tumours. On DWI, all PNETs were hyperintense and had restricted apparent diffusion coefficient. MRS (two patients with medulloblastoma and one with a SPNET), showed elevated choline, decreased N-acetyl aspartate, and a small taurine peak in all three patients. Intraspinal tumour dissemination, visible as uniform or nodular enhancement coating the conus medullaris, was detected in six of 12 patients, two of whom also had intracranial dissemination. CONCLUSION: PNETs have a characteristic imaging appearance on FLAIR, DWI and MRS, which may help in differentiating these highly cellular neoplasms from other tumours. There is CSF tumour dissemination in a high proportion of patients, and spinal imaging is important for disease staging and to formulate treatment protocols.

MR spectroscopy in sinus mucocele: N-acetyl mimics of brain N-acetylaspartate.

We describe MR spectroscopy in 2 patients with frontal sinus mucoceles that showed a dominant metabolite peak at 2.0-ppm chemical shift, simulating N-acetylaspartate (NAA) of normal neuronal tissue. In vitro analysis of postsurgical mucocele samples confirmed that the signal at 2.0 ppm was arising from the methyl moiety of an N-acetyl compound. This is probably caused by N-acetylgalactosamine or N-acetylglucosamine, which are glycoproteins found in normal respiratory mucus produced by the paranasal sinus epithelium.

Independent component analysis of dynamic contrast-enhanced computed tomography images.

Independent component analysis (ICA) was applied on dynamic contrast-enhanced computed tomography images of cerebral tumours to extract spatial component maps of the underlying vascular structures, which correspond to different haemodynamic phases as depicted by the passage of the contrast medium. The locations of arteries, veins and tumours can be separately identified on these spatial component maps. As the contrast enhancement behaviour of the cerebral tumour differs from the normal tissues, ICA yields a tumour component map that reveals the location and extent of the tumour. Tumour outlines can be generated using the tumour component maps, with relatively simple segmentation methods.

Assessment of perfusion by dynamic contrast-enhanced imaging using a deconvolution approach based on regression and singular value decomposition.

The assessment of tissue perfusion by dynamic contrast-enhanced (DCE) imaging involves a deconvolution process. For analysis of DCE imaging data, we implemented a regression approach to select appropriate regularization parameters for deconvolution using the standard and generalized singular value decomposition methods. Monte Carlo simulation experiments were carried out to study the performance and to compare with other existing methods used for deconvolution analysis of DCE imaging data. The present approach is found to be robust and reliable at the levels of noise commonly encountered in DCE imaging, and for different models of the underlying tissue vasculature. The advantages of the present method, as compared with previous methods, include its efficiency of computation, ability to achieve adequate regularization to reproduce less noisy solutions, and that it does not require prior knowledge of the noise condition. The proposed method is applied on actual patient study cases with brain tumors and ischemic stroke, to illustrate its applicability as a clinical tool for diagnosis and assessment of treatment response.

Clinics in diagnostic imaging (91). Subarachnoid haemorrhage.

Computed tomography (CT) is the initial radiological investigation of patients with an acute neurological event. A 64-year-old woman presenting with generalised weakness and headache for two days was diagnosed on CT to have subarachnoid haemorrhage. Digital subtraction angiography confirmed the cause to be a ruptured posterior communicating artery aneurysm. The patient was treated by neuroradiological intervention using occlusive coils. The CT features of subarachnoid haemorrhage are discussed. Accurate CT interpretation is essential to direct appropriate investigations and management in patients with stroke, particularly as acute cerebral infarction may occasionally mimic subarachnoid haemorrhage. The role of magnetic resonance (MR) imaging in evaluation of cerebral infarct is also discussed.

Late clinical and magnetic resonance imaging follow up of Nipah virus infection.

The Nipah virus is a newly identified paramyxovirus responsible for an outbreak of fatal encephalitis in Malaysia and Singapore. This paper reports the follow up clinical and magnetic resonance imaging findings in 22 affected subjects. Of 13 patients with encephalitis, one died, one was lost to follow up, and seven recovered. Among the four remaining patients, one had residual sixth nerve palsy, another suffered from severe clinical depression, and a third patient had evidence of retinal artery occlusion. One patient with delayed onset Horner syndrome had a single lesion in the cervical spinal cord. The brain magnetic resonance findings were stable or improved in nine patients over 18 months of follow up. Among a second group of nine asymptomatic seropositive abattoir workers, magnetic resonance examination in seven subjects revealed discrete small lesions in the brain; similar to those detected in encephalitis patients. These findings suggest that in addition to encephalitis, the newly discovered Nipah virus affects the spinal cord and the retina. Late clinical and radiological findings can occur in Nipah virus infections as with other paramyxoviruses.

Rising signal intensity observed in extra-axial brain tumours - a potential pitfall in perfusion MR imaging.

OBJECTIVE: Dynamic perfusion magnetic resonance (MR) techniques may be used to track the susceptibility effects of gadolinium contrast material as it passes through the brain. We describe three intracranial tumours that showed progressively rising signal intensity above the baseline during first-pass contrast-enhanced echo-planar imaging (EPI) MR imaging. METHODS: Multiphase acquisition using single-shot EPI was performed during rapid bolus contrast injection. Ten studies, using either spin-echo or gradient-echo EPI sequences, were carried out in eight patients with intracranial tumours. Time-signal intensity graphs and regional cerebral blood volume (rCBV) were reviewed. RESULTS: In seven studies, the signal intensity within the tumour showed initial signal drop and quick recovery to baseline and increased rCBV. Three studies revealed progressively rising signal intensity. These patients were all imaged using a spin-echo EPI method and subsequent histology revealed meningioma, hemangiopericytoma and pinealblastoma. CONCLUSION: Dynamic perfusion MR methods may be used to study intracranial tumours. However, in short relaxation time spin-echo EPI, the T1- effect of gadolinium becomes noticeable during the first-pass acquisition in extra-axial tumours that lack a well-developed blood-brain barrier. Careful selection of patients and pulse sequence is essential to avoid this potential pitfall.