Week 8 Abdominal Imaging Flashcards
What are common important problems in abdominal imaging?
Small bowel obstruction
Large bowel obstruction
Pneumoperitoneum or bowel perforation
foreign body
What are the different densities on X rays?
The more dense and object the whiter it appears on xray.
White - bone, foreign object (intensely white) , calcification
Grey - soft tissues, fat appears darker grey than other soft tissue (absorbs less x rays, less dense)
Black - air
Key landmarks of this abdominal xray?
Starting on the Left at the top going down:
Liver
R kidney
Left transverse process of L1
Ascending colon
Right psoas major muscle
?
R pelvis Iliac fossa
R femur (neck)
Right side starting from top going down:
Splenic flexure
Transverse colon
Left kidney
left 11th rib
descending colon
Left pedicle of L3
Spinous process L4
Left sacroiliac joint
Bladder
How do you tell the difference between small and large bowel on an xray?
Small bowel features - more central position (usually framed within the large bowel) and has valvulae conniventes (lines the cross the whole diameter of the bowel). Smaller diameter - around 5cm
Large bowel features - more peripheral position and pouches/ sacculations that protrude into the lumen - haustra - that do not fully cross the bowel diameter. Large bowel hangs off the mesentery therefore it is not always in the typical position. Large diameter - 8cm
Faeces usually have mottled appearance and are visible within the large bowel (due to trapped gas).
General approach to an abdominal xray? (not details steps just overall approach)
1) patient details Name/DOB/identification number
2) Date and time on Xray
3) assess quality of the xray:
Projection –> AP supine or AP erect?
Exposure –> Whole abdomen visible? (from dipahragm to the pelvis)
Note if bowel perforation is suspected then you need an erect CXR to see free gas under the diaphragm, pt upright for 20 mins prior.
4) BBC approach
5) Bowels –> small, large Bowel, lungs, Liver, gallbladder, stomach, psoas muscles, Kidney’s, spleen, bladder
6) Bones –> Ribs, lumbar vertebrae, Sacrum, coccyx, pelvis, proximal femurs
7) Calcifications –> Arterfacts and renal stones
What are the general rules for bowel diameter on abdominal xray?
3: 6: 9 Rule where upper limits of the normal diameter of different bowel segments are:
No more than 3cm for small bowel
No more than 6 cm for large bowel
No more than 9 cm for the caecum
What features should you be checking for when assessing the bowel on an abdominal xray?
1st –> differentiate between small and large bowel, small bowel less than 5cm diameter, valvulae conniventes, mostly central. Large bowel around 8cm diameter, hausta, more peripheral location.
2nd –> asses diameters of each 3: 6: 9 rule
3rd –> look for features of small or large bowel obstruction
4th –> Assess for pneumoperitoenum –> Riglers double wall sign –> gas outlining both the inside of the bowel and the outside of the bowel (normally only see the inside line). If suspecting pneumoperitoneum need to request erect CXR.
5th –> look for features of IBD (later card)
What are the xray features of a small bowel obstruction?
Most common cause of small bowel obstruction?
Signs:
- Diameter of small bowel > 3cm
- Dilated small bowel proximal to obstruction
- small bowel disproportionately dilated and large bowel less visible (collapsed as no movement of chyme into large bowel)
- Dilated small portions become fluid filled –> may see multiple fluid-air levels.
- Prominent valvulae conniventes - “coiled spring” appearance
Causes:
- Adhesions are the most common cause (related to prior bowel surgery)
- others are hernias (always assess the inguinal regions in abdominal xray).
- or external compression by tumour/ mass
- Crohns / gallstones/ foreign object.
What are the most common causes of large bowel obstruction?
What are the x-ray features of large bowel obstruction?
- Causes of large bowel obstruction:
- Colorectal carcinoma (60%)
- Diverticular strictures
- volvulus –> caecal and sigmoid volvulus. Volvulus = twisting of the bowel on its own mesentery, most common locations at the caecum and sigmoid colon. High risk of bowel perforation and/ or bowel ischaemia.
- faecal impaction –> elderly
- intussusception
- hernia (uncommon)
- Xray features:
- Colonic distention proximal to the obstruction and collapse distally
- very few air fluid levels found distally as water is reabsorbed.
- rectum has little or no air
- advanced cases might have perforation and pneumoperitoneum
What are the two types of volvulus?
What are the xray features of each type of volvulus?
Caecal and sigmoid volvulus:
Sigmoid = coffee bean appearance, large dilated portion of colon at lower end of pelvis, absent rectal gas. Very few air fluid levels.
Caecal = fetal appearance, Dilated bowel proximal to the caecum, caecum diameter greater than 9cm, distended caecum may be seen anywhere in the abdomen, often colonic haustra appearance maintained (not in sigmoid volvulus).
What is Riglers double wall sign?
what other investigation should be done?
Sign of pneumoperitoneum on xray –> usually only see inside of the bowel (due to gas within bowel lumen), do not usually see gas outside the bowel, therefore if see double wall –> sign of pneumoperitoneum.
Request erect cxr.
How would small bowel obstruction present?
abdominal pain and distention
Typically colicky in nature
N & V
Constipation
Prior hx of bowel or abdominal surgery
Bowel sounds hypeactive and high pitched –> if absent worried about bowel ischaemia
How would large bowel obstruction present?
Abdominal pain and distention
failure to pass faeces or flatusV
N & V
if perforated –> peritonitis features such as rebound tenderness and sepsis features (low BP, Raised HR/RR)
What are the features of IBD on Abdo xray?
- Thumbprinting –> mucosal thickening of haustra projecting into the lumen due to inflammation and oedema –> appears like thumbprints
- Lead pipe or featureless colon –> due to chronic colitis, loss of haustra.
- Toxic megacolon –> colonic dilatation without obstruction due to colitis
How would you assess the other structures/ organs in an abdominal xray?
- Lungs –> inspect lung bases for consolidation, basal pneumonia can sometimes cause abdominal pain
- liver –> RUQ, enlargement or nodules etc
- gallbladder –> Rarely visible, inspect for gallstones or cholecystectomy clips
- stomach –> visible between LUQ and midline, gastric air bubble
- spleen –> LUQ superior to left kidney
- bladder –> look for stones, variable appearance depending on fullness
How would you assess bones on Abdominal xray?
- Ribs, lumbar vertebrae, pelvis, sacrum and coccyx, proximal femur
- Look for sclerotic lesions or any signs of metastases
What calcifications or arterfacts may be seen on abdominal xray?
- Gallstones
- renal stones
- calcifiied pancreas
- vascular calcifications (e.g. atherosclerotic lesion, outside of vascular tree becomes calcified in aneurysm)
- costchondral calcification
- surgical clips
- jewellery
