Neonatal Abdominal Radiography

Introduction

'Cotside' abdominal radiography in the neonatal unit presents a number of radiographic challenges. This page considers the radiographic techniques required for particular pathologies and line placements.

The number of attachments makes for a high level of complexity and a significant array of potential artifacts.

Abbreviations and Terminology

UAC: UVC: ETT: NGT: TPT: VP Shunt: CVC: VLBW: NEC:

Umbilical artery catheter Umbilical vein catheter Endotracheal tube Nasogastric tube Transpyloric tube Ventriculo-peritoneal shunt Central Venous Catheter Very Low Birthweight Necrotising Enterocolitis

Ground Rules

You learn quickly that radiography in the neonatal unit is different. The patients are very small, vulnerable and sometimes very ill. The following are some very simple dot point tips:

• wash your hands before entering the unit and on exiting. Also, wash your hands between babies (important)
• ensure that the baby's name matches the one on the request form (careful you don't get confused with twins)
  
• check the clinical information on the request form- this can influence what you include on the image
  
• don't run the mobile machine into the cot/incubator (surprisingly easy to do)
• ask the nurses for help- they know the babies, know their illnesses, and are used to handling them
• be careful to avoid patient rotation, particularly with chest radiography
• use a side marker (see Baker Cone)- left and right are not always clear from the anatomy, particularly in chest radiography
• check departmental protocol re removal of ECG leads
• think about radiation protection- horizontal ray technique considerations, gonad protection, long bone protection, the nurse's fingers
  
• you are not the boss- if the nurse says the baby can't be moved..the baby can't be moved.
• use a cassette tray if there is one built into the cot/isolette

Technique Tips

• I have noticed that some radiographers set an approximate neonatal exposure (kV, mAS) in advance i.e. before they leave for the unit, on the way, or on arrival at the unit. The reason for this is that the previous exposure might be an adult exposure. It is possible that in concentrating on the positioning task that you might overlook setting the exposure. This could be a disaster if the previous exposure was for an adult abdomen in ICU with a grid (I have seen it happen). This practice is not required if there is a dedicated mobile X-ray machine for the neonatal unit.
  

Radiation Protection

Operator Irradiation

The person holding the baby can receive an undesirable bonus image of their fingers. This is largely avoided by education, coning and diligence. The nurse holding the baby may not be as aware of the significance of her fingers in the LBD light as you are. It is worthwhile pointing out to the nurse that 'where the light is the radiation is- this might seem self-evident to you, but possibly the nurse might be less aware than you are of the primary X-ray beam

Side Markers

Side markers in the neonatal unit are important. The difficulty is that your side marker can appear to be almost as big as the baby's chest. There are three solutions that I am aware of Baker Cones Baker cones are pieces of lead rubber that have the side marker punched into them. Dedicated Neonatal Markers The side marker on the left is simply too large for use in the Neonatal Unit. You don't want to collimate out to include this relatively large marker. The side marker on the left is the type used by the radiographers at the Adelaide Womens and Childrens Hospital. They also use these small side markers with the operator's initials. Importantly, the operator's initials are engraved laterally on the marker- to the right on a right marker and to the left on a left marker. This ensures that if the marker is partly collimated off, it is the operator's initials that are collimated off and not the "L" or "R". Lead on Plastic Markers These markers work on the opposite principle to brass engraved markers. They are usually a lead letter stuck onto a plastic base material. The image from these markers is less bulky/conspicuous than that produced by a brass engraved side marker

Left Lateral Decubitus

This is the preferred decubitus position. The free intraperitoneal gas is seen easily because it is contrasted against the liver. Although it is described as a "left lateral decubitus" it is marked with a right marker.

Right Lateral Decubitus

The right lateral decubitus abdominal projection(right side down) is not the decubitus of choice. The preferred decubitus is the left lateral decubitus- left lateral decubitus is more sensitive for pneumoperitoneum. This is, nevertheless, an acceptable decubitus position when the left lateral decubitus cannot be achieved. This is also arguably preferable to a dorsal (supine) decubitus. Operators phalanges noted in image.

Supine Decubitus

The dorsal (supine) decubitus is a projection that can be employed when horizontal ray abdominal radiography is required in a patient that cannot be moved. This technique can be equally employed in adults, children and neonates. It is important to note that this technique is usually employed as a last resort. Despite its limitations, I would suggest that it is good radiography to adopt this view in preference to giving up. If the referring doctor is looking for free intraperitoneal gas (pneumoperitoneum), it is important to include all of the anterior abdominal wall. Raising the baby onto a positioning sponge to improve the radiographic image is both counterproductive and of no diagnostic benefit when looking for free gas. i.e. the advantage of this technique is that you don't move the baby. The removal of all ECG leads where appropriate will improve the image. I suspect these ECG leads were removed and placed next to the baby- arguably better to keep them out of the field altogether.

The baby's right arm is superimposed over the chest/abdomen (white arrow). This is highly undesirable when you are looking for free gas sited at the lateral aspect of the liver

Imperforate Anus

There is a specific abdominal radiography technique for imperforate anus. The position and image are shown below.

Inverted lateral rectum position <a class="external" href="http://books.google.com.au/books?id=vgHF3KvGFzcC&pg=PA126&lpg=PA126&dq=neonatal+radiography&source=web&ots=j0frDYgDKU&sig=wpdDsFTjxLl5wtz0z3Eb5K-cydU&hl=en&sa=X&oi=book_result&resnum=6&ct=result#PPA125,M1" rel="nofollow" target="_blank">Source: Maryann Hardy and Stephen Boynes, Paediatric Radiography, 2003</a>	Horizontal ray lateral rectum with lead shot marker indicating the position of the anus Source: Maryann Hardy and Stephen Boynes, Paediatric Radiography, 2003

Inguinal Hernia

The arrowed structure is air in bowel which has herniated into the scrotum. Clearly, if this anatomy had not been included on the image, the diagnosis would have been missed. If the request form suggests that there is a possibility of inguinal hernia, the scrotum should be included in the abdominal image (unnatural as that may be). If the request form lists "obstruction" as a differential diagnosis, ask the referring doctor if he/she wants the scrotum included.

This baby has an inguinal hernia with air-filled bowel within the scrotum (bottom arrow) The artifact is an umbilical clamp (top arrow)

Tubes, Lines and Catheters

You may be called to the Neonatal Unit to confirm the position of a line, tube or catheter. A knowledge of these lines will be useful in determining which anatomy should be included on the image (i.e. it will determine your beam coning).

Umbilical Catheters

UVC

• The umbilical vein is 2-3cm long and 4-5mm in diameter
• From the umbilicus, it passes cephalad and a little to the right. It joins the left branch of the portal vein after giving off several large intrahepatic branches.
• The ductus venosus arises from the point where the UV joins the left portal vein.

UAC

• The umbilical arteries are the direct continuation of the internal iliac arteries.
• A catheter passed into an umbilical artery will usually (but not always) enter the aorta via the internal iliac artery.
• Occasionally it will pass into the femoral artery via the external iliac artery or into the gluteal arteries.
• The femoral and gluteal arteries are unsuitable sites for sampling, infusion, or blood pressure monitoring.<a class="external" href="http://www.adhb.govt.nz/newborn/Guidelines/VascularCatheters/UmbilicalCatheters.htm#UAC" rel="nofollow" target="_blank">source</a>

There are two potential positions for the UAC. These are described as "high" or "low".

• The high position is at the level of thoracic vertebral bodies T6-T9. This position is above the coeliac axis (T12), the superior mesenteric artery (T12-L1), and the renal arteries (L1). This position is essentially "above the diaphragm".
• The low position is at the level of lumbar vertebral bodies L3-L4. This position is below the structures as above, and is above the aortic bifurcation (L4-L5). The inferior mesenteric artery arises from L3-L4. This position is essentially "above the bifurcation". <a class="external" href="http://www.adhb.govt.nz/newborn/Guidelines/VascularCatheters/UmbilicalCatheters.htm#UAC" rel="nofollow" target="_blank">source</a>

<img align="bottom" alt="Umbilical catheter position" height="600" src="http://image.wikifoundry.com/image/1/GWJuIjLId0OcSBW_Q3X4rg131678/GW450H600" title="Umbilical catheter position" width="450"/>

The umbilical catheters are inserted through the umbilicus into either the umbilical vein or the umbilical artery. The umbilical artery catheter (UAC) characteristically deviates inferiorly before tracking up the aorta. See the lateral decubitus abdominal image below for further appreciation of the course of the umbilical artery. The umbilical vein catheter takes a completely different course along the umbilical vein. See also below Double lumen catheters can be used in babies who are very sick and may require significant support

The UAC and UVC are seen in this dorsal decubitus abdominal image. UAC The umbilical artery catheter (UAC) can be seen to track inferiorly and posteriorly from the umbilicus before tracking up the aorta. UVC The umbilical vein catheter(UVC) takes a shorter course along the umbilical vein. NGT The nasogastric tube enters the stomach from the oesophagus. When assessing the position of the NGT the position of the sidehole should also be considered.

Nasogastric Tube

The Nasogastric tube (NGT) can be seen to have its tip well placed in the stomach. If the X-ray request makes it clear that the X-ray examination is for NGT position only, the lower half of the abdomen does not need to be included. If in doubt- ask. It is worth making sure that a NGT and not a TPT has been inserted- see below.

Transpyloric Tube and VP Shunt

The transpyloric tube (TPT) is similar to a nasogastric tube (NGT) except that it is longer and intended to have its tip sited distal to the pyloris. The ventriculo-peritoneal shunt provides a drainage path from the ventricles of the brain to the peritoneal cavity This image does not cover the entire length of the VP shunt- it should be complemented by a lateral skull view. Alternatively, I have seen radiographers employ a "head and torso" lateral approach in one image.

Central Venous Catheter (CVC) Longline- leg

The central venous catheter has been inserted in the right leg and its tip is difficult to localise precisely. This is a common problem with CVC lines and emphasises the need for good quality images when checking CVC lines. A study of printed CR images vs soft copy CR images reported a long line detection rate of 66.7% vs 95.6% respectively. <a class="external" href="http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1721656&blobtype=pdf" rel="nofollow" target="_blank">(A Evans, J Natarajan, C J Davies, 2004).</a> Other suggestions include "The authors emphasise the importance of verifying neonatal long line position using contrast, as the exact localisation of the catheter tip can be difficult on plain radiographs. As an alternative, Groves et al have described the use of colour Doppler to aid ultrasonographic line tip visualisation." <a class="external" href="http://fn.bmj.com/cgi/content/extract/91/4/F311" rel="nofollow" target="_blank">T M Berger, M Stocker, J Caduff</a> Gonad protection could have been used to good effect

A magnified view demonstrates the CVC tip to be at the level of the first sacral vertebra. This is an "actual pixels" image i.e. one pixel in the image is one pixel on the screen. This demonstrates the advantage of viewing images by 'softcopy' rather than hardcopy

Central Venous Catheter (PICC) - arm

The technique issues are much the same as for a leg longline. Include the arm of interest and a good exposure is required. A softcopy digital image is best.

The tip of the longline is in the proximal brachiocephalic vein. (lower white arrow) The top white arrow identifies the endotracheal tube (ETT) The black arrow identifies the nasogastric tube (NGT)

The tip of the right arm PICC line is hard to see (arrow). The tip of the PICC line is much easier to see on the enlarged image on the right.	This image is an "actual pixels" image. Any larger than this and you will lose detail.

Case Study

The radiographer was called to the Neonatal Unit and requested to undertake a chest/abdominal X-ray examination on one of the premature babies to establish the position of the double lumen Umbilical Vein Catheter (UVC). The image is shown below

The tube at the top of the screen is the endotracheal tube (ETT) with its tip in close proximity to the carina There are three ECG leads (unmarked) The black arrow points to an umbilical catheter which appears to be in the arterial side (UAC). Note that the UAC dips down (as it enters the umbilicus) before changing direction - this is characteristic of a UAC rather than the UVC. The tip of the UAC is at the level of T8. The stomach is airfilled. The umbilical venous catheter (UVC) appears to be kinked (middle white arrow) The lower white arrow identifies an oval shaped radiolucent structure that does not correspond with any hollow abdominal viscus. The radiographer thought that this represented pneumoperitoneum. The radiographer was called back to the neonatal unit for abdominal radiography on the same baby 1 hour later. It was assumed that this was for a decubitus abdominal projection to prove the pneumoperitoneum. This was not the case- the umbilical venous catheter had been repositioned and this was a check X-ray. The pneumoperitoneum was not suspected by the neonatal unit staff. The radiographer asked if the abdominal image could be performed in the horizontal ray decubitus position. This was agreed to and the image is shown below.

The horizontal ray decubitus abdominal image confirmed the pneumoperitoneum. The lateral edge of the baby's liver is contrasted against the free intraperitoneal gas. The UVC has been unkinked. The ideal position for the UVC is above the diaphragm but below the heart. The baby's left arm is superimposed over the left hemithorax

Discussion

This page covers a range of radiographic techniques, interventions and pathologies that you might encounter in a neonatal unit. An awareness of this material will make a trip to the neonatal unit more meaningful and possibly more effective.

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