Extracorporeal membrane oxygenation (ECMO)

1. Extracorporeal membrane oxygenation for 2009 Influenza (H1N1) ARDS - ANZ ECMO influenza investigators. Journal: JAMA, Oct 19, 2009 A descriptive analysis of all adult and paediatric (neonates excluded) patients treated with ECMO, 1st june - 31 August 2009 in Australia, NZ ICU's during 2009 H1N1 epidemic. In 200 ICUs, 15 supplied ECMO for 61 (32%) of 194 H1N1/ Influenza A ventilated patients with 21% mortality. All these patients met inclusion criteria for the CESAR trial. to be continued..

MRI pearls

1. FLAIR - fluid attenuated inversion recovery sequence eliminates the signal from CSF. it is sensitive to oedema and inflammation. Axial T2 FLAIR: nulls the normally bright T2 signal of CSF (becomes black), while other parenchymal fluid appears bright (as in oedema or tumour).


2. Diffusion Weighted Imaging (DWI) DWI assesses the movement of protons due to diffusion over a short time. If there is restricted diffusion the signal is of high intensity. If there is unrestricted diffusion (e.g. CSF), there is low intensity signal. Unfortunately the signal on DWI is not just produced by the diffusion characteristics but also changes in parallel with the T2 and PD of the tissue. To eliminate these cofounders an apparent diffusion coefficient (ADC) map is generated. The ADC signal is low with true restricted diffusion. Using a combination of these sequences vasogenic oedema (intensity high on T2, high on DWI and high on ADC map) may be distinguished from cytotoxic oedema (intensity high on T2, high on DWI and reduced on ADC map).


3. Gadolinium contrast: Gd is a paramagnetic substance that acts as a contrast agent by markedly shortening T1 when it is present. Gd based contrast distributes throughout the extracellular fluid, and does not cross the normal BBB. In pathological conditions in which the BBB breaks down, there is marked hyper-intensity (enhancement) of affected areas on T1 weithted images.

Radiology pearls 3 --> subaxial cervical spine and thoracolumbar spine

subaxial cervical spine - C3 to C7

The classification of injury is based on the mechanism of injury. The patterns are distraction, compression, flexion and extension. Then there are distractive flexion, distractive extension, compressive flexion and compressive extension injuries.

A. On sagittal reconstructions, check for the following:

• anterior and posterior vertebral body lines and spinolaminar line are uninterrupted
• vertebral body height is the same anteriorly and posteriorly
• no prevertebral swelling
• no widening of distances between spinous process
• facet joints aligned, appearing as stacked parallelograms
• disc spaces intact

B. On coronal images check the following:

• height on each side of the vertebral body is the same
• disc spaces are intact
• facet joints are aligned

C. On axial images check the following:

• no soft tissue swelling
• facet joints aligned
• no significant rotation

i. compressive extension injury:

there is damage to the vertebral arch but the body remains intact. The vertebral arch fractures may be unilateral or bilateral, involving the pedicle, articular process, the lamina or a combination of these. In more severe injuries, the affected vertebra may be displaced anteriorly relative to the subjacent vertebra. The antero superior aspect of the subjacent vertebra may be sheared off.

ii. compressive flexion injury:

• stage 1 - there is blunting of the anterior-superior vertebral margin.
• stage 2 - there is a beak like appearance to the anterioe vertebral body with loss of anterior vertebral height and oblique contour.
• stage 3 -there is fracture extending from anterior surface of the vertebral body into the disc space.
• stage 4 - there is posterior displacement of the inferoposterior aspect of the vertebral body less than 3 mm.
• stage 5 -displacement relative to the vertebra below is more than 3 mm

iii. distractive extension injury

• stage 1 -abnormal widening of the disc space, representing disruption of the anterior longitudinal ligament and disc
• stage 2 - posterior ligaments are disrupted and the cephalad vertebtrae are displaced into the spinal canal

iv. distractive flexion injury:

range from facet subluxation, through unilateral facet fracture or dislocation to bilateral facet joint fracture or dislocation.

v. vertical compression

• stage 1: there is central fracture of either the superior or inferior endplate with a cupping deformity of the endplate.
• stage 2: bothe endplates are involved.
• stage 3: the vertebral body is fragmented with fragments displaced in multiple directions. The vertebral arch may not be involved.

Thoracolumbar spine

Classification of injury is based on three column concept. Columns of thoracic spine are anterior, middle and posterior. common injury patterns are compression fractures, burst fractures, flexion distraction (seat belt type), and fracture dislocations.

The anterior column:is formed by the anterior longitudinal ligament, the anterior half of the vertebral body and the anterior annulus fibrosus.

Middle column: posterior longitudinal ligament, the posterior half of the vertebral body and posterior annulus fibrosus.

Posterior column: posterior osseous arch, supraspinous and interspinous ligaments, the ligamentum flavum and the facet joint capsule.

The features sought on sagittal, coronal and axial images of the T-L spine are similar to those described for lower cervical spine injuries.

i. compression fracture:

the anterior column fails under compression. The middle column remains intact and acts as a hinge. The posterior column is usually intact but with severe injuriew it may partially fail in distraction. This injury may be anterior or lateral.

ii. burst fractures:

there is failure of compression of the anterior and middle columns, but no posterior column. Failure in compression of the anterior column is shown by fracture of the cortex of the anterior vertebral body, which loses height. Failure in compression of the middle column is shown by similar findings in the posterior vertebral body. Characteristically the pedicles are spread apart by the posterior vertebral body fracture. There is commonly a vertical fracture of the lamina, and splaying of the facet joints, without which there could not be significant widening of the interpedicular distance.

iii. flexion distraction "seat-belt type" injury:

there is failure in distraction of the middle and posterior columns with either no injury to the anterior column or minor compression. The injury may be through bone, through the ligaments or a combination of the two. When injury is through the bone at one level, it is known as "chance" fracture. There is a high incidence (around 60%) of intra-abdominal injury in association with flexion-distraction injuries.

iv. fracture dislocation:

failure of all three columns leading to translational deformity (sublaxation or dislocation) which may be in the sagittal or coronal plane. Fracture dislocation of thoracic spine occur with high energy trauma.

Fracture dislocations involve all three column making them extremely unstable injuries, commonly associated with neurological damage.

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Clearing the C-spine

The best approach to clearing the cervical spine with multiple trauma remains controversial. In this group of patients, plain XRay miss a significant proportion of bony cervical injuries. A single cross table lateral view missed 37% of significant injuries. A three view series missed 10% while cervical spine CT missed none. Ligamentous injuries are not well imaged with CT scan. When multiple trauma patients are imaged with CT scan, 6% have discoligamentous injuries that are not detected.

CT is the imaging modality of choice in this group of patients with supplementary MRI when spinal cord of ligamentous injury is suspected.

Radiology pearls 2 -craniocervical junction

Craniocervical junction: the skull base, atlas and axis form the craniocervical junction that in conjunction with associated ligaments acts as a single functional unit.
A. On sagittal CT images check for the following:

1. atlanto dental space should be less than 3 mm in adult and less than 5 mm in child
2. anterior cortex of the odontoid peg and posterior cortex of anterior arch of C1 are parallel
3. anterior aspects of the laminae of C1-C3 are in alignment, the spinolaminar line
4. bodies of C2 and C3 are in alignment with a normal disc space
5. no sublaxation or widening of the atlanto occipital joints
6. facet joints between C1/C2 and C2/C3 are aligned

B. On axial images check the following:

1. space between anterior arch of C1 and the odontoid peg should be less than 3 mm
2. C1 is symmetrically aligned around the odontoid peg
3. no significant rotation of C0/C1 or C1/C2
4. absence of soft tissue swelling

C. On coronal images, check the following:

1. space between odontoid peg and lateral mass of C1 is the same on both sides
2. there is no sublaxation or widening of the atlanto-occipital joints
3. the facet joints between C1/C2 and C2/C3 are aligned
4. the edge of the lateral mass of C1 does not over hang C2 at the facet joint

The major ligaments of the craniojunction are:

1. the paired alar ligaments that extend from the odontoid peg to the medial aspect of the occipital condyles
2. the posterior longitudinal ligament that runs posterior to the vertebral bodies and extends as the tectorial membrane to insert into basion
3. the anterior longitudinal ligament that runs anterior to the vertebral bodies and extends as anterior atlanto occipital membrane to insert into the basion
4. the transverse atlantal ligament that extends between the lateral masses of C1, passing posterior to the odontoid peg.

Occipitocervical dissociation

occipitocervical dissociation which is also known as atlanto-occipital sublaxation is easily missed on plain radiography, and is potentially fatal!

It maybe

• type 1 - anterior sublaxation
• type 2 -vertical distraction of atlanto-occipital joint more than 2 mm, or
• type 3 - posterior dislocation

CT Brain pearls -1

CT features suggesting elevated ICP include:

• effacement of basal cisterns
• loss of grey-white differentiation
• loss of sulci
• midline shift
• herniation of cerebellar tonsils into the foramen magnum
• uncal herniation

The features of uncal herniation are:

• shift of the brainstem and distortion of adjacent cisterns
• dilatation of contralateral temporal horn
• compression of the posterior cerebral artery as it crosses the tentorium, causing a posterior cerebral artery territory infarct

PATTERN OF BRAIN HERNIATION

• Uncal transtentorial herniation: the uncinate process of the temporal lobe herniates into the anterior part of the opening of the tentorium cerebelli.
• Central tentorial herniation: there is symmetrical downward movement of the thalamic region through the opening of the tentorium cerebelli
• Subfalcine herniation: there is displacement of the cingulate gyrus under the falx and across the midline
• Foraminal herniation: there is downward herniation of the cerebellar tonsils into the foramen magnum

The level of foramen magnum is measured on the saggital T1 image. It is defined as a line between the front (basion) and the back (opisthion) of the foramen magnum. The signal of cortical bone, not marrow must be used to define these landmarks.

Brain herniation

There are two type of cerebral oedema:

1. Cytotoxic: intracellular oedema caused by cell swelling with an intact blood brain barrier. Cytotoxic oedema affects predominantly grey matter, with subsequent loss in grey-white matter differentiation. It generally accompanies stroke and hypoxia and gives a pattern of "restricted diffusion" on MRI sequences

2. Vasogenic: extracellular oedema caused by loss of integrity of the BBB. Vasogenic odema predominantly affects white matter and spreads along white matter tracts, accentuating the grey-white matter differentiation. It generally accompanies inflammatory disease and brain tumors. It does not give a pattern of "restricted diffusion" on MRI sequences.

http://en.wikipedia.org/wiki/Brain_herniation

Radiological signs suggesting aortic disruption

Hi again,
This week I am studying radiology. Certain essential knowledge must be remembered by heart. There is a classic constellation of signs on the chest X-Ray associated with aortic injury. (Clarke 1977):

1. Displacement of trachea and NG tube to the right
2. Wide upper mediastinum
3. Left pleural cap
4. Loss of aorto-pulmonary window, the space on the left mediastinal border between the aortic knuckle and the pulmonary artery.
5. Indistinct outline of aortic knuckle
6. Depression of left main bronchus
7. Fracture of first or second rib
8. Left haemothorax
9. Loss of paratracheal stripe

CT angiography, TEE or DSA would be acceptable for investigation of a possible traumatic rupture of the aorta. MRA may be used, but the requirement for prolonged investigation in a suboptimally monitored environment limits its usefullness.