Dural masses: meningiomas and their mimics.

Meningiomas are the most common dural tumour. They are regularly being seen as an incidental finding on brain imaging and treated conservatively. However, there are many other dural masses which mimic their appearances, including primary neoplastic processes, metastases, granulomatous diseases and infection. While some of these are rare, others such as metastases and tuberculosis arise relatively frequently in practice. Although not pathognomonic, key features which increase the probability of a lesion being a meningioma include intralesional calcifications, skull hyperostosis, local dural enhancement and increased perfusion. It is important to have an awareness of these entities as well as their main imaging findings, as they have a wide range of prognoses and differing management strategies. This review outlines several of the most important mimics along with their imaging findings on both standard and advanced techniques with key features which may be used to help differentiate them from meningiomas.

Pineal and leptomeningeal metastases from a parotid carcinoma ex pleomorphic adenoma.

Carcinoma ex pleomorphic adenoma (CEPA) is an uncommon complication of an untreated pleomorphic adenoma (PA), but one that has a life-threatening significance. This case report documents the clinical, radiological and histopathological features of an extremely rare case of biopsy-proven pineal metastasis, with cerebellopontine and leptomeningeal spread, from CEPA of the parotid gland in spite of the patient having undergone parotidectomy, ipsilateral neck dissection and adjuvant radiotherapy. In spite of the current surgical and oncological treatment of CEPA, the rates of recurrence and distant metastases are high, with a subsequently poor prognostic outcome in most patients. Distant spread is usually to the bones and the lungs; however, more unusual locations have been documented. Our finding of pineal metastasis from CEPA has not previously been reported in the literature. Although this is a rare complication of an unusual condition, the aggressive behaviour of these malignancies warrants close clinical follow-up, with a low threshold for re-imaging and investigation if indicated.

New vistas in clinical practice: susceptibility-weighted imaging.

Susceptibility-weighted imaging (SWI) is a recently developed magnetic resonance imaging (MRI) technique where image contrast represents 'magnetic susceptibility effects'-a natural property of tissues. The applications of SWI are rapidly increasing, with much work being carried out to determine the usefulness of the technique in multiple disease states. Current clinical applications of the technique include detection of microbleeds, subarachnoid hemorrhage (SAH), ferromagnetic deposition in neurodegenerative disease, and characterization of cerebral tumors.

Analysis of image heterogeneity using 2D Minkowski functionals detects tumor responses to treatment.

PURPOSE: The acquisition of ever increasing volumes of high resolution magnetic resonance imaging (MRI) data has created an urgent need to develop automated and objective image analysis algorithms that can assist in determining tumor margins, diagnosing tumor stage, and detecting treatment response. METHODS: We have shown previously that Minkowski functionals, which are precise morphological and structural descriptors of image heterogeneity, can be used to enhance the detection, in T1 -weighted images, of a targeted Gd(3+) -chelate-based contrast agent for detecting tumor cell death. We have used Minkowski functionals here to characterize heterogeneity in T2 -weighted images acquired before and after drug treatment, and obtained without contrast agent administration. RESULTS: We show that Minkowski functionals can be used to characterize the changes in image heterogeneity that accompany treatment of tumors with a vascular disrupting agent, combretastatin A4-phosphate, and with a cytotoxic drug, etoposide. CONCLUSIONS: Parameterizing changes in the heterogeneity of T2 -weighted images can be used to detect early responses of tumors to drug treatment, even when there is no change in tumor size. The approach provides a quantitative and therefore objective assessment of treatment response that could be used with other types of MR image and also with other imaging modalities.

A comparison of MR elastography and 31P MR spectroscopy with histological staging of liver fibrosis.

OBJECTIVES: Conventional imaging techniques are insensitive to liver fibrosis. This study assesses the diagnostic accuracy of MR elastography (MRE) stiffness values and the ratio of phosphomonoesters (PME)/phosphodiesters (PDE) measured using (31)P spectroscopy against histological fibrosis staging. METHODS: The local research ethics committee approved this prospective, blinded study. A total of 77 consecutive patients (55 male, aged 49 ± 11.5 years) with a clinical suspicion of liver fibrosis underwent an MR examination with a liver biopsy later the same day. Patients underwent MRE and (31)P spectroscopy on a 1.5 T whole body system. The liver biopsies were staged using an Ishak score for chronic hepatitis or a modified NAS fibrosis score for fatty liver disease. RESULTS: MRE increased with and was positively associated with fibrosis stage (Spearman's rank = 0.622, P < 0.001). PME/PDE was not associated with fibrosis stage (Spearman's rank = -0.041, p = 0.741). Area under receiver operating curves for MRE stiffness values were high (range 0.75-0.97). The diagnostic utility of PME/PDE was no better than chance (range 0.44-0.58). CONCLUSIONS: MRE-estimated liver stiffness increases with fibrosis stage and is able to dichotomise fibrosis stage groupings. We did not find a relationship between (31)P MR spectroscopy and fibrosis stage. KEY POINTS: Magnetic resonance elastography (MRE) and MR spectroscopy can both assess the liver. MRE is superior to ( 31 ) P MR spectroscopy in staging hepatic fibrosis. MRE is able to dichotomise liver fibrosis stage groupings. Gradient-echo MRE may be problematic in genetic haemochromatosis.

Imaging of congenital and acquired disorders of the pulmonary artery.

The pulmonary artery is affected by a multitude of conditions that can be congenital or acquired. These disorders may be detected incidentally, or the clinical features of the different conditions may overlap. This pictorial review illustrates the imaging findings of some of the main conditions that affect the pulmonary artery by considering them in 3 main categories: congenital disorders; enlargement of the pulmonary arteries, most commonly seen in pulmonary hypertension; obstruction or occlusion of the pulmonary arteries, as seen in thromboembolic disease or large vessel vasculitis. It is important for the radiologist to understand the radiological manifestations of these disorders, as early recognition would be of significant benefit in their diagnosis and treatment.

Characterization of image heterogeneity using 2D Minkowski functionals increases the sensitivity of detection of a targeted MRI contrast agent.

A targeted Gd(3+)-based contrast agent has been developed that detects tumor cell death by binding to the phosphatidylserine (PS) exposed on the plasma membrane of dying cells. Although this agent has been used to detect tumor cell death in vivo, the differences in signal intensity between treated and untreated tumors was relatively small. As cell death is often spatially heterogeneous within tumors, we investigated whether an image analysis technique that parameterizes heterogeneity could be used to increase the sensitivity of detection of this targeted contrast agent. Two-dimensional (2D) Minkowski functionals (MFs) provided an automated and reliable method for parameterization of image heterogeneity, which does not require prior assumptions about the number of regions or features in the image, and were shown to increase the sensitivity of detection of the contrast agent as compared to simple signal intensity analysis.

Detection of cell death in tumors by using MR imaging and a gadolinium-based targeted contrast agent.

PURPOSE: To prospectively determine in an animal model whether an ionic gadolinium (Gd(3+)) chelate conjugate of the C2A domain of synaptotagmin I can be used with magnetic resonance (MR) imaging to detect tumor cell death noninvasively in vivo. MATERIALS AND METHODS: Animal experiments were approved by a local ethics review committee. Gd(3+) chelates and fluorescent probes were attached to the lysine epsilon-amino groups of a glutathione-S-transferase-C2A fusion protein. Binding to phosphatidylserine (PS) was characterized by using surface plasmon resonance, and binding to dying cells in vitro was characterized by using flow cytometry and MR imaging. Binding to dying tumor cells in vivo was detected with T1 mapping and T1-weighted MR imaging and compared in drug-treated animals (n = 10); in animals injected with a site-directed mutant, which was inactive in PS binding (PS inactive) and which showed lesser binding to dying cells (n = 6); and in untreated animals injected with PS-active (n = 6) and PS-inactive (n = 6) contrast agents. Among groups, differences that were significant were analyzed by using analysis of variance and Dunnett post hoc analysis. RESULTS: The contrast agent had a relatively high affinity for PS (dissociation constant = 333 nmol/L +/- 85 [mean +/- standard error of the mean]; n = 3) and bound to apoptotic and necrotic, but not viable, cells in vitro. There was a greater tumor accumulation of the PS-active contrast agent compared with the PS-inactive contrast agent in drug-treated animals (P < .05) and compared with untreated animals injected with the PS-active and PS-inactive contrast agents (P < .01 for both). CONCLUSION: A relatively small (approximately 100 kDa) Gd(3+)-based contrast agent, which gives positive contrast on MR images, can be used to detect tumor cell death in vivo, and future derivatives of it may be used to assess early tumor responses to treatment.

A paramagnetic nanoprobe to detect tumor cell death using magnetic resonance imaging.

A 110 kDa (ca. 5 nm in diameter) bivalent paramagnetic nanoprobe for detecting cell death using magnetic resonance imaging (MRI) is described, in which two biotinylated C2A domains of the protein synaptotagmin-I were complexed with a single avidin molecule, which had been labeled with gadolinium chelates. This nanoprobe bound with high affinity and specificity to the phosphatidylserine exposed by dying cells and was demonstrated to allow MRI detection of apoptotic tumor cells in vitro.