Abdominal X-ray Radiological Signs

Suzanne O’Hagan

Lightbulb momenta moment of sudden inspiration, revelation, or recognition

Approach to AXR

• Bowel gas pattern

• Extraluminal air

• Soft tissue masses

• Calcifications

Normal AXR11th rib

Hepatic flexure

Gas in stomach

T12

Gas in caecum

Iliac crest

Femoral head

SI joint

Gas in sigmoid

Transverse colon

Splenic flexure

Psoas margin

Sacrum

Left kidney

Liver

Bladder

Gas pattern

• Stomach– Almost always air in stomach

• Small bowel– Usually small amount of air in

2 or 3 loops

• Large bowel– Almost always air in rectum

and sigmoid– Varying amount of gas in rest of large bowel

What is normal?

Normal fluid levels• Stomach

– Always (upright, decub)

• Small bowel– Two or three levels

acceptable (upright, decub)

• Large bowel– None normally

(functions to remove fluid)

Large vs small bowel

• Large bowel– Peripheral (except RUQ occupied by liver)– Haustral markings don’t extend from wall to wall

• Small bowel– Central– Valvulae conniventes extend across lumen and are

spaced closer together

Radiographic principles

Series of films for acute abdomen• Obstruction series/ Acute abdominal series/

Complete abdominal series

– Supine (almost always)– Upright or left decubitus (almost always)– Prone or lateral rectum (variable)– Chest, upright or supine (variable)

VIEW LOOK FOR

SUPINE ABDOMEN Bowel gas patternCalcificationsMasses

PRONE ABDOMEN Gas in rectosigmoidGas in ascending and descending colon

UPRIGHT ABDOMEN Free air, air-fluid levels

UPRIGHT CHEST Free air, lung pathology secondary to intraabdominal process

Acute abdominal seriesWhat to look for

Substitutes: Prone Lateral rectum Upright Left lateral decub Upright chest Supine chest

Obtaining views• Supine

– Patient on back, x ray beam directed vertically downward, casette posterior, x-ray tube anterior (AP)

• Prone– Patient on abdomen, x-ray beam

directed vertically downward, cassette anterior, x-ray tube posterior (PA)

• Upright– Patient stands or sits, x-ray beam

directed horizontally, cassette posterior, x-ray tube anterior (AP)

• Upright chest– Patient stands or sits, horizontal x-ray

beam, cassette anterior, x-ray tube posterior (PA) 1900s X-Ray-based fluoroscopy machine

in which radiation is shot directly through the patient and into the doctor’s face.

Abnormal Gas Patterns

• Functional ileus– One or more bowel loops become aperistaltic usually

due to local irritation or inflammation• Localised “sentinel loops” (one or two loops)• Generalised (all loops of large and small bowel)

• Mechanical obstruction– Intraluminal or extraluminal

• Small bowel obstruction• Large bowel obstruction

3, 6, 9 RULE

Maximum Normal Diameter of bowel

Small bowel 3cm

Large bowel 6cm

Caecum 9cm

Localised ileusKey features

• One or two persistently dilated loops of small or large bowel (multiple views)

• Often air-fluid levels in sentinel loops

• Local irritation, ileus in same anatomical region as pathology

• Gas in rectum or sigmoid• May resemble early SBO

Causes of Localised Ileusby location

SITE OF DILATED LOOPS CAUSE

Right upper quadrant Cholecystitis

Left upper quadrant Pancreatitis

Right lower quadrant Appendicitis

Left lower quadrant Diverticulitis

Mid-abdomen Ulcer or kidney/ureteric calculi

Colon cut off sign

Explanation:

Inflammatory exudate in acute pancreatitis extends into the phrenicocolic ligament via lateral attachment of the transverse mesocolon

Infiltration of the phrenicocolic ligament results in functional spasm and/or mechanical narrowing of the splenic flexure at the level where the colon returns to the retroperitoneum.

Abrupt cutoff of colonic gas column at the splenic flexure (arrow). The colon is usually decompressed beyond this point.

Generalised ileusKey features

• Entire bowel aperistaltic/hypoperistaltic• Dilated small bowel and large bowel to rectum

(with LBO no gas in rectum/sigmoid)• Long air-fluid levels

CAUSE REMARK

*Postoperative Usually abdominal surgery

Electrolyte imbalance Diabetic ketoacidosis

* almost always

Generalised adynamic ileus

The large and small bowel are extensively airfilled but not dilated.

The large and small bowel "look the same".

Mechanical SBO

• Dilated small bowel

• Fighting loops (visible loops, lying transversely, with air-fluid levels at different levels)

• Little gas in colon, especially rectum

SBO Erect SBO Supine

Air fluid levels

Causes of Mechanical SBO

* May be visible on AXR

Adhesions

Hernia*

Malignancy

Gallstone ileus*

Intussesception

Inflammatory bowel disease

Step ladder appearance

• Loops arrange themselves from left upper to right lower quadrant in distal SBO

Coil spring sign

String of pearls sign

Considered diagnostic of obstruction (as opposed to ileus) and is caused by small bubbles of air trapped in the valvulae of the small bowel.

Stretch/slit sign

Slit of air caught in a valvulae, characteristic of SBO

Closed loop obstruction• Two points of same loop of bowel obstructed

at a single location• Forms a C or a U shape

– Term applies to small bowel, usually caused by adhesions

– Large bowel, called a volvulus

Crescent Sign

Caused by:

LUQ Soft tissue mass

OR

Head of intussusception in distal transverse colon

Double Bubble Sign

Duodenal Atresia

Mechanical LBO• Colon dilates from point

of obstruction backwards

• Little/no air fluid levels (colon reabsorbs water)

• Little or no air in rectum/sigmoid

Large bowel obstructionBowel loops tend not to overlap therefore possible to identify site of obstruction

Little or no gas in small bowel if ileocaecal valve remains competent*

* If incompetent, large bowel decompresses into small bowel, may look like SBO

Causes of Mechanical LBO

TUMOUR

VOLVULUSHERNIADIVERTICULITISINTUSSUSCEPTION

Note on volvulus

• Sigmoid colon has its own mesentry therefore prone to twisting

• Caecum usually retroperitoneal and not prone to twisting; 20% people have defect in peritoneum that covers the caecum resulting in a mobile caecum

VolvulusA volvulus always extends away from the area of twist.Sigmoid volvulus can only move upwards and usually goes to the right upper quadrant. Caecal volvulus can go almost anywhere.

Coffee Bean SignSigmoid volvulus

Massively dilated sigmoid loop

Hernia

Lateral decubitus of valueThe advantage is that there may be a greater chance of air entering the

herniated bowel because it is the least dependent part of the bowel in the supine position.

Apple core sign

• Radiologic manifestation of a focal stricture of the bowel usually at contrast material enema examination. The stricture demonstrates shouldered margins and resembles the core of an apple that has been partially eaten. The most common cause is an annular carcinoma of the colon.

Thumbprinting

The distance between loops of bowel is increased due to thickening of the bowel wall.

The haustral folds are very thick, leading to a sign known as 'thumbprinting.'

Lead pipe colon

• Shortening of colon secondary to fibrosis

• Loss of haustration

• Ulcerative colitis

Extraluminal air• TYPES

– Pneumoperitoneum/free air/intraperitoneal air

– Retroperintoneal air

– Air in the bowel wall (pneumatosis intestinalis)

– Air in the biliary system (pneumobilia)

Upright film best

• The patient should be positioned sitting upright for 10-20 minutes prior to acquiring the erect chest X-ray image.

• This allows any free intra-abdominal gas to rise up, forming a crescent beneath the diaphragm. It is said that as little as 1ml of gas can be detected in this way.

Free AirCauses

• Rupture of a hollow viscus– Perforated peptic ulcer– Trauma– Perforated diverticulitis (usually seals off)– Perforated carcinoma

• Post-op 5-7 days normal, should get less with successive studies *NOT ruptured appendix (seals off)

Signs of free air• Crescent sign• Chilaiditis sign• Riglers (and False Rigler’s)• Football sign• Falciform ligament sign• Triangle sign• Cupola sign• Lesser sac sign

Crescent Sign IIFree air under the diaphragm

Best demonstrated on upright chest x rays or left lat decub

Easier to see under right diaphragm

Chilaiditis sign

• May mimic air under

the diaphragm• Look for haustral folds• Get left lat decub to

confirm

In patients who have cirrhosis or flattened diaphragms due to lung hyperinflation, a void is created within the upper abdomen above the liver. This space may be filled by bowel. If this bowel is air filled then it may mimic free gas.

Rigler’s Sign Bowel wall visualised on both sides due to intra and extraluminal airUsually large amounts of free airMay be confused with overlapping loops of bowel, confirm with upright view

False Rigler’s Sign

• The Rigler sign can sometimes be simulated by contiguous loops of bowel, whereby intraluminal air in one loop of bowel may appear to outline the wall of an adjacent loop, which results in a misdiagnosis of free air.

• Measure distance of interface if unsure

Football SIgn

Seen with massive pneumoperitoneum

Most often in children with necrotising enterocolitis

Paediatric Adult

In supine position air collects anterior to abdominal viscera

Falciform ligament sign

Normally invisible.

Supine film, free air rises over anterior surface of liver

Other patterns of air around liver

Doge’s Cap Sign

Inverted V sign

• On the supine radiograph, an inverted "V" may be seen over the pelvis in a patient with pneumoperitoneum.

• While in infants this is produced by the umbilical arteries, in adults it appears to be created by the inferior epigastric vessels

Continuous diaphragm sign

Sufficient free air, left and right hemi- diaphragmsappear continous

Lesser sac Sign Cupola Sign

Lesser sac sign

– (black arrows)

The lesser sac is positioned posterior to the stomach and is usually a potential space. There is free connection between the lesser sac and the greater sac through the foramen of Winslow

Cupola

sign – (white

arrows)

Air superior to left lobe of liver

Double Bubble Sign

Cupola Sign

The term cupola comes from a dome such as

this famous dome of the Duomo in Florence.

Air beneath the central tendon of the diaphragm

Triangle Sign

• The triangle sign refers to small triangles of free gas that can typically be positioned between the large bowel and the flank

Retroperitoneal Air• Recognised by:

– Streaky, linear appearance outlining retroperitoneal structures

– Mottled, blotchy appearance– Relatively fixed position

• May outline:– Psoas muscles– Kidneys, ureters, bladder– Aorta or IVC– Subphrenic spaces

Causes of retroperitoneal air

• Bowel perforation (appendix, ileum, colon)• Trauma (blunt or penetrating)• Iatrogenic• Foreign body• Gas producing infection

Pneumoretroperitoneum

• This patient has free air in the retroperitoneal space. The air is seen surrounding the lateral border of the right kidney (white arrow). There is other evidence of free gas including Rigler's sign.

• If you are not confident that the appearance is pneumoretroperitoneum, you can try an erect and decubitus view to see if the gas moves. If the gas is seen to move, it's not in the retroperitoneum.

Air in the bowel wall• Signs

– Best seen in profile producing a linear lucency that parallels the bowel

– Air en face has a mottled appearance resembling gas mixed with faeculent material

Causes of air in bowel wall

• Primary Pneumatosis cystoides intestinalis (rare)– usually affects left colon– Produces cyst-like collections of air in the submucosa or serosa

• Secondary– Diseases with bowel wall necrosis– Obstructing lesions of the bowel that raise intraluminal pressure

• Complications– Rupture into peritoneal cavity– Dissection of air into portal venous system

Pneumatosis intestinalis

• Intramural air, best appreciated in profile

Air in the biliary tree

• One or two tube-like branching lucencies in the RUQ, conform to location of major bile ducts

Causes

• “Normal” if Sphincter of Oddi incompetence• Previous surgery including sphincterotomy or

transplantation of CBD

• Pathology (uncommon)– Gallstone ileus: gallstone erodes through wall of

GB into the duodenum producing a fistula between the bowel and the biliary system.

– Stone impacts in small bowel = mechanical SBO. “ileus” misnomer

Biliary vs Portal Venous Air

• Portal venous air usually associated with bowel necrosis

• Air is peripheral rather than central

• Numerous branching structures

Soft tissue masses• Organomegaly

– Know normal landmarks

2 ways to identify soft tissue masses/organs:

– Direct visualisation of edges of structure– Indirect by displacement of bowel

CT, US and MRI have essentially replaced conventional radiography in the assessment of organomegaly and soft tissue masses

Location Pattern

Abdominal Calcifications

First exclude artefact

Kim Kardashian’s butt – real or artefact?

Location• Vascular• Liver• Gallbladder• Spleen• Pancreas• Lymph nodes• Adrenals • Kidneys• Ureters• Bladder• Prostate

Rim-like• Calcification that has occurred in the wall of a

hollow viscus

– Cysts • renal, splenic, hepatic

– Aneurysms • aortic, splenic, renal artery

– Saccular organs• Gallbladder• Urinary bladder Calcified hydatid cysts

Linear/Track

• Calcification in walls of tubular structures

– Arteries– Fallopian tubes– Vas deferens– Ureter

Aortoiliac calcification

Chinese Dragon Sign

Calcified splenic artery

Calcified vas deferens

Floccular, Amorphous, Popcorn

• Formed in solid organ or tumour– Pancreas (chronic pancreatitis)– Leiomyomas of uterus– Ovarian cystadenomas– Lymph nodes– Adenocarcinomas of stomach, ovary, colon– Metastases– Soft tissue (previous trauma, crystal deposition)

Calcified enteric lymph nodes

Calcified fibroids

Calcified pancreas

Floccular

Lamellar or laminar

• Formed around a nidus inside hollow lumen

• Concentric layers due to prolonged movement of stone inside hollow viscus– Renal stones– Gallstones– Bladder stones

Bladder calculi

Lamellar

Renal calculiPelvicalyceal calcifications

Staghorn Calcification

Renal stones are often small, but if large can fill the renal pelvis or a calyx, taking on its shape which is likened to a staghorn.Tubular

Nephrocalcinosis

Uncommonly the renal parenchyma can become calcified.

This is known as nephrocalcinosis, a condition found in disease entities such as medullary sponge kidney or hyperparathyroidism.

Renal calculiParenchymal calcification

Flocculent

Putty Kidney

• "Putty kidney" – sacs of casseous, necrotic material (TB)

• Autonephrectomy – small, shrunken kidney with dystrophic calcification

Flocculent

Calcified gallstones

Lamellar

Conclusion

• Approach to AXR should include gas pattern, extraluminal air, soft tissue and calcifications

• Named radiological signs are a useful way of remembering, identifying and reporting on films

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22, 1369-1384• Young, L. Radiology Cases in Paediatric Emergency Medicine. Vol 1 Ca 2. The Target, Crescent and

Absent Liver Edge Signs.• Raymond, B et al. Radiographics: Classic signs in uroradiology. RSN 2004• http://www.swansea-radiology.co.uk Radiology Teaching Site. Introduction to abdominal

radiography• Mussin, R. Postgrad Med J 2011: 87:274-287. Gas patterns on plain abdominal radiographs• http://www.radiologymasterclass.co.uk/tutorials/abdo/abdo_x-ray_abnormalities• Mettler: Essentials of Radiology, 2nd Ed, 2005• http://www.learningradiology.com/radsigns• Muharram Food signs in radiology. International Journal of Health Sciences Vol 1 No 1. Jan 2007.

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