Maurits Voormolen

Trauma of the spine and spinal cord: imaging strategies

Traumatic injuries of the spine and spinal cord are common and potentially devastating lesions. We present a comprehensive overview of the classification of vertebral fractures, based on morphology (e.g., wedge, (bi)concave, or crush fractures) or on the mechanism of injury (flexion-compression, axial compression, flexion-distraction, or rotational fracture-dislocation lesions). The merits and limitations of different imaging techniques are discussed, including plain X-ray films, multi-detector computed tomography (MDCT), and magnetic resonance imaging (MRI) for the detection. There is growing evidence that state-of-the-art imaging techniques provide answers to some of the key questions in the management of patients with spine and spinal cord trauma: is the fracture stable or unstable? Is the fracture recent or old? Is the fracture benign or malignant? In summary, we show that high-quality radiological investigations are essential in the diagnosis and management of patients with spinal trauma.

Magnetic Resonance Imaging of the Brain

Magnetic resonance imaging (MRI) examinations of the brain can be performed with several coil types, depending on the design of the MRI unit and the information required. Traditionally, MRI examinations of the brain are performed with quadrature (i.e., circularly polarized) head coils. These volume coils are closely shaped around the head of the patient and usually present a so-called “bird-cage” configuration. Many coils are split in half, for easier patient access and positioning. Recently, phased-array head coils have become the standard of practice for state-of-the-art high-resolution MRI of the brain. Phased-array head coils contain multiple small coil elements, which are arranged in an integrated design which surrounds the head (e.g., 8-, 12- or even 32-channel head coils). Data from the individual coils are integrated by special software to compensate for the nonuniform distribution of the signal-to-noise ratio (SNR) between the peripheral and central parts of the brain. The major advantage of a multichannel, phased-array head coil is that it allows the application of parallel acquisition techniques (PAT), which can be used to speed up MRI. The concept is to reduce the number of phase-encoding steps by switching a field gradient for each phase-encoding step. Skipping, for example, every second phase-encoding line accelerates the acquisition speed by a factor of two. This is called the acceleration or PAT factor. The trade-off for this increased imaging speed is a decrease in SNR. Image reconstruction with PAT techniques is more complicated, and several algorithms have been described, depending on whether image reconstruction takes place before (SMASH, GRAPPA (generalized autocalibrating partially parallel acquisition)) or after (SENSE) Fourier transform of the image data.

Neural tonotopy in cochlear implants: An evaluation in unilateral cochlear implant patients with unilateral deafness and tinnitus

In cochlear implants, the signal is filtered into different frequency bands and transmitted to electrodes along the cochlea. In this study the frequency-place function for electric hearing was investigated as a means to possibly improve speech coding by delivering information to the appropriate cochlear place. Fourteen subjects with functional hearing in the contralateral ear have been provided with a MED-EL cochlear implant in the deaf ear in order to reduce intractable tinnitus. Pitch scaling experiments were performed using single-electrode, constant-amplitude, constant-rate stimuli in the implanted ear, and acoustic sinusoids in the contralateral ear. The frequency-place function was calculated using the electrode position in the cochlea as obtained from postoperative skull radiographs. Individual frequency-place functions were compared to Greenwoods function in normal hearing. Electric stimulation elicited a low pitch in the apical region of the cochlea, and shifting the stimulating electrode towards the basal region elicited increasingly higher pitch. The frequency-place function did not show a significant shift relative to Greenwoods function. In cochlear implant patients with functional hearing in the non-implanted ear, electrical stimulation produced a frequency-place function that on average resembles Greenwoods function. These results differ from previously derived data.

Degenerative Disc Disease

The spinal column is a complex anatomical structure which is composed of vertebrae, intervertebral discs, and ligaments. All components undergo degenerative changes and morphologic alterations during life (Prescher 1998). In this chapter we shall focus our attention on the intervertebral discs, which are also referred to as “intervertebral fibrocartilages”; the two terms can be used interchangeably (Warwick and Williams 1973). From the axis (C2) to the sacrum, the intervertebral discs are situated between the upper and lower endplates of adjacent vertebral bodies. They constitute the principal connections between the vertebrae, and have two main functions: to serve as shock absorbers, and to allow movement of the spinal column. Movement at a single disc level is limited, but all of the vertebrae and discs combined allow for a significant range of motion (Inoue and Takeda 1975).

Frequency-place map for electrical stimulation in cochlear implants: Change over time

The relationship between the place of electrical stimulation from a cochlear implant and the corresponding perceived pitch remains uncertain. Previous studies have estimated what the pitch corresponding to a particular location should be. However, perceptual verification is difficult because a subject needs both a cochlear implant and sufficient residual hearing to reliably compare electric and acoustic pitches. Additional complications can arise from the possibility that the pitch corresponding to an electrode may change as the auditory system adapts to a sound processor. In the following experiment, five subjects with normal or near-to-normal hearing in one ear and a cochlear implant with a long electrode array in the other ear were studied. Pitch matches were made between single electrode pulse trains and acoustic tones before activation of the speech processor to gain an estimate of the pitch provided by electrical stimulation at a given insertion angle without the influence of exposure to a sound processor. The pitch matches were repeated after 1, 3, 6, and 12 months of experience with the sound processor to evaluate the effect of adaptation over time. Pre-activation pitch matches were lower than would be estimated by a spiral ganglion pitch map. Deviations were largest for stimulation below 240° degrees and smallest above 480°. With experience, pitch matches shifted towards the frequency-to-electrode allocation. However, no statistically significant pitch shifts were observed over time. The likely explanation for the lack of pitch change is that the frequency-to-electrode allocations for the long electrode arrays were already similar to the pre-activation pitch matches. Minimal place pitch shifts over time suggest a minimal amount of perceptual remapping needed for the integration of electric and acoustic stimuli, which may contribute to shorter times to asymptotic performance.

Genomewide association study identifies no major founder variant in Caucasian moyamoya disease

Moyamoya disease (MMD) is an idiopathic cerebrovascular occlusive-stenosis disorder at the terminal portion of internal carotid arteries and its main branches, accompanied by collateral vascular networks at the base of the circle of Willis (Takeuchi and Shimizu 1957; Suzuki and Takaku 1969). MMD has the highest prevalence in East Asian countries and a low prevalence in European countries (Goto and Yonekawa 1992; Kuroda and Houkin 2008). We have found that the p.R4810K variant in the ring finger protein 213 (RNF213) is a major founder susceptibility gene for East Asian MMD (Liu et al. 2010, 2011). In this study, we aimed to test whether there is a major founder susceptibility gene for Caucasian MMD using a genomewide association study (GWAS). We demonstrated that there was no major founder variant in Caucasian MMD as it is in East Asian MMD. We identified several suggestive association regions for Caucasian MMD.

Microsurgical removal of Onyx HD-500 from an aneurysm for relief of brainstem compression. Case report.

The authors report the successful removal of Onyx HD-500 from an aneurysm sac by means of ultrasonic aspiration. This 46-year-old woman presented with progressive spasms of her left arm and leg due to mass effect and compression on the right cerebral peduncle 5 years after endovascular treatment of an unruptured giant posterior communicating artery aneurysm with Onyx HD-500. No filling of the aneurysm was detected on angiography. The patient underwent a right pterional craniotomy and the aneurysm was opened to remove the Onyx mass. However, contrary to expectations, the aneurysm was still patent, filling with blood between the Onyx mass and the aneurysm wall. Under temporary clipping of the carotid artery, the Onyx mass within the aneurysm was removed in a piecemeal fashion using an ultrasonic aspirator and the aneurysm was then successfully clipped. The patient experienced significant improvement of the spasm after surgery. Angiography showed complete occlusion of the posterior communicating artery aneurysm. It is rarely necessary to remove embolization material such as Onyx HD-500, and little is known about the most appropriate surgical technique. This case report demonstrates that removal can be safely accomplished by means of ultrasonic aspiration.

Spontaneous closure of cerebral dural arteriovenous fistulas with direct cortical venous drainage. A case report.

We describe two rare cases of spontaneous closure of cerebral dural arteriovenous fistulas (DAVFs) with a small nidus and draining directly in a single cortical vein with several ectasias. Eighteen previously published cases of spontaneous closure of cerebral DAVF comprised more benign fistula types. In literature, several explanations for DAVF occlusion have been proposed. We hypothesize that, in addition to the known causes, the specific contrast medium used during the diagnostic selective angiography might have played a role in the thrombosis and subsequent fistula closure.

Intraventricular thrombolysis for massive intraventricular hemorrhage due to periventricular arteriovenous malformations: No absolute contraindications as rescue therapy prior to surgical repair or embolization?

Intraventricular hemorrhage (IVH) after bleeding from a cerebral aneurysm or an arteriovenous malformation (AVM) results in a high mortality. A limited number of publications have shown that intraventricular thrombolysis with e.g. recombinant tissue plasminogen activator (rt-PA) can be a therapeutic option in IVH. However, this treatment is considered as an absolute contraindication prior to the treatment of the bleeding source. We report the successful use of low-dose intraventricular thrombolysis (rt-PA) in two cases of life-threatening intraventricular hemorrhage due to periventricular AVMs as rescue therapy, even prior to source control of the bleeding. Our observations, together with nine comparable published cases, illustrate that this treatment might be useful to clear the intraventricular blood and lower intracranial pressure. It might also improve neurological outcome and mortality in these selected patients. This suggests that hemorrhage from a periventricular AVM, even before surgical resection or endovascular embolization, is not necessarily an absolute contraindication for intraventricular thrombolysis in patients with massive IVH.

Brain stones revisited—between a rock and a hard place

Objectives and methodsLarge intracranial calcifications are occasionally encountered in routine computed tomography (CT) scans of the brain. These calcifications, also known as “brain stones”, can be classified according to location and aetiology. Combining imaging findings with relevant clinical history and physical examination can help narrow down the differential diagnosis and may allow confident diagnosis in certain situations.ResultsThis article provides a pictorial review illustrating various clinical entities resulting in brain stones.DiscussionBased on location, brain stones can be classified as extra- or intra-axial. Extra-axial brain stones comprise tumours and exaggerated physiological calcifications. Intra-axial brain stones can further be classified according to aetiology, namely neoplastic, vascular, infectious, congenital and endocrine/metabolic. Imaging findings combined with essential clinical information can help in narrowing the differential diagnosis, determining disease state and evaluating effect of therapy.Teaching Points• Based on location, brain stones can be either extra- or intra-axial.• Extra-axial brain stones comprise tumours and exaggerated physiological calcifications.• Intra-axial aetiologies include neoplastic, vascular, infectious, congenital and endocrine/metabolic.• CT scan is the mainstay in identifying and characterising brain stones.• Certain MRI sequences (gradient echo T2* and susceptibility-weighted imaging) are considered adjunctive.