The anterior pararenal space is the portion of the retroperitoneum that lies between the posterior surface of the parietal peritoneum and the anterior reflection of the perirenal fascia.
It contains the duodenum (D2 & D4), pancreas and retroperitoneal segments of the ascending an...
Anterior resection syndrome refers to wide spectrum of symptoms which develop post-sphincter preserving rectal resection for rectal cancer.
Pelvic radiotherapy is a known risk factor to develop anterior resection syndrome.
There have been reports that up to 47% of patients who un...
The anterior right subhepatic space is a potential space between the inferior surface of the right lobe of the liver and the transverse colon.
The anterior right subhepatic space is separated from Morison’s pouch (also known as the posterior right subhepatic space) by the transve...
Anthrax is a zoonosis caused by Bacillus Anthracis. There are four types of anthrax: inhalational anthrax (also known as woolsorter's disease and ragsorter's disease), cutaneous anthrax, injection anthrax and intestinal anthrax.
The disease burden of anthrax decreased so dramatica...
Antibiotic-associated diarrhea can be broadly divided into two groups:
Clostridioides difficile colitis
The former is a life-threatening condition, requiring prompt diagnosis and treatment whereas the later is milder and self-limiting.
Both result from changes in the b...
Antineutrophil cytoplasmic antibodies (ANCAs) are a heterogenous class of IgG autoantibodies raised against the cellular contents of neutrophils, monocytes and endothelial cells 1. Under indirect immunofluorescence (IIF) microscopy, three ANCA staining patterns are observed, based on the varying...
Antiphospholipid syndrome is a systemic autoimmune disorder. It is usually defined as the clinical complex of vascular occlusion and ischemic events occurring in patients who have circulating antiphospholipid antibodies.
Antiphospholipid syndrome is characterized by venou...
The antral nipple sign refers to redundant pyloric mucosa protruding into the gastric antrum and is seen in hypertrophic pyloric stenosis on ultrasound examination.
cervix sign (pyloric stenosis)
target sign (pyloric stenosis)
The antral pad sign is a feature seen on a spot radiograph of the upper gastrointestinal tract obtained with orally-administered contrast material. It refers to the extrinsic impression or indentation on the posteroinferior aspect of the antrum. The impression is generally arcuate and smooth, an...
The aortic hiatus is one of the three major apertures through the diaphragm and lies at the level of T12. Strictly speaking, it is not a real aperture in the diaphragm, but an osseoaponeurotic opening between it and the vertebral column.
The hiatus is situated slightly to the left of the midli...
Aortoenteric fistulas are pathologic communications between the aorta (or aortoiliac tree) and the gastrointestinal tract and represent an uncommon cause of catastrophic gastrointestinal hemorrhage.
Aortic fistulas may be considered primary (associated with a complicated abdominal aortic aneury...
Aphthoid ulcers are shallow ulcers of the gastrointestinal mucosa.
infective inflammatory conditions
noninfective inflammatory conditions
idiopathic granulomatous gastritis
Appendiceal carcinoids are rare overall but represent the most common tumor of the appendix. The appendix is also one of the most common (but not the most common) locations for gastrointestinal carcinoid tumors.
Appendiceal carcinoids can present as the obstructive cause...
Appendiceal diverticulitis (plural diverticulitides) is a rare condition in which there is acute inflammation of a diverticulum arising from the vermiform appendix.
Historically appendiceal diverticulitis has been thought to be a rare diagnosis. However a study from 2015 which ret...
Appendiceal intussusception happens when appendix segment is pulled into itself or into the cecum. This condition can mimic various chronic and acute abdominal conditions. It is an important entity to recognize since it could be mistaken for a cecal mass.
Appendiceal mucoceles occur when there is an abnormal accumulation of mucin causing abnormal distention of the vermiform appendix due to various neoplastic or non-neoplastic causes.
The reported prevalence at appendectomy is 0.2-0.3%. They are thought to typically present in middl...
Appendicitis is inflammation of the vermiform appendix. It is a very common condition in general radiology practice and is one of the main reasons for abdominal surgery in young patients. CT is the most sensitive modality to detect appendicitis.
Acute appendicitis is typically a d...
This is a basic article for medical students and other non-radiologists
Appendicitis occurs when there is inflammation of the vermiform appendix. It is a very common condition and is a major cause of abdominal surgery in young patients. CT is the most sensitive modality to detect appendicitis a...
An appendicolith is a calcified deposit within the appendix. They are present in a large number of children with acute appendicitis and may be an incidental finding on an abdominal radiograph or CT. Incidence may be increased among patients with a retrocecal appendix. Overall they are seen in 10...
Appendicular abscess is considered the most common complication of acute appendicitis, in particular after a perforated appendix.
Appendicular abscesses can arise either in the peritoneal cavity or the retroperitoneal space.
Ultrasound is the first investiga...
The appendicular artery is a branch of the ileal or posterior cecal branch of the ileocolic artery, which is from the superior mesenteric artery.
It courses posteriorly to the terminal ileum in the free wall of the mesoappendix to supply the appendix.
The appendix or vermiform appendix (plural: appendices) is a blind muscular tube that arises from the cecum, which is the first part of the large bowel.
The appendix arises from the posteromedial surface of the cecum, approximately 2-3 cm inferior to the ileocecal valve, where th...
The Appleby procedure is a type of pancreatic cancer resection.
For some patients with pancreatic cancer involving the body and tail of the pancreas, involvement of the celiac axis is a classic contraindication to pancreaticoduodenectomy (Whipple procedure).
With the Appleby procedure, there...
The apple core sign, also known as the napkin ring sign (bowel), is most frequently associated with constriction of the lumen of the colon by a stenosing annular colorectal carcinoma.
The appearance of the apple-core lesion of the colon also can be caused by other diseas...
The apple core sign has been described in two different pathologies:
apple core sign (colon)
apple core sign (femur)
Apple-peel intestinal atresia, also known as type IIIb or Christmas tree intestinal atresia, is a rare form of small bowel atresia in which the duodenum or proximal jejunum ends in a blind pouch and the distal small bowel wraps around its vascular supply in a spiral resembling an apple peel. Oft...
The arc of Buhler (AOB) is a persistent embryonic anastomotic branch between the 10th and 13th ventral segmental arteries, resulting in a connection between the celiac artery and superior mesenteric artery (SMA). This arch is independent of both the gastroduodenal and dorsal pancreatic artery.
The arc of Riolan, also known as the mesenteric meandering artery (of Moskowitz) or central anastomotic mesenteric artery, is an arterioarterial anastomosis between the superior and inferior mesenteric arteries.
It is an inconstant artery that connects the proximal superior mesen...
Areae gastricae are a normal finding on double contrast images of the stomach.
fine reticular network of barium-coated grooves between 1-5 mm islands/areas of gastric mucosa
may be seen in ~70-80% of patients if there is adequate high-density barium coating of the stomac...
A rings are a type of distal esophageal ring. They are above the B ring and occur a few centimeters proximal to the gastro-esophageal junction. They represent a physiological contraction of esophageal smooth muscle covered by mucosa. A rings are uncommonly symptomatic.
The arrowhead sign refers to the focal cecal thickening centered on the appendiceal orifice, seen as a secondary sign in acute appendicitis. The contrast material in the cecal lumen assumes an arrowhead configuration, pointing at the appendix.
The arrowhead sign is applicable only when enteri...
Arterial occlusive mesenteric ischemia can be a life-threatening event related to obstruction of the mesenteric arteries, most commonly the superior mesenteric artery (SMA), supplying the small bowel and colon. It is the most common cause of mesenteric ischemia.
An acute occlusi...
Asbestos-related disease, in particular affecting the lung, comprise of a broad spectrum of entities related to the inhalational exposure to asbestos fibers. They can be divided into benign and malignant processes 1-3.
Benign pleural and parenchymal lung disease
asbestos-related benign pleural...
Ascariasis is due to infection with the Ascaris lumbricoides adult worm and typically presents with gastrointestinal or pulmonary symptoms, depending on the stage of development.
Ascaris lumbricoides is widely distributed in tropical and subtropical regions and in other humid ar...
Ascaris-induced pancreatitis is the most common form of parasite-induced pancreatitis.
Ascariasis in parts of India is the second most common form of pancreatitis after gallstones 1. It is rare outside of endemic regions however.
The presentation will be si...
The ascending colon is the second part of the large bowel.
The ascending colon is the continuation of the cecum superior to the ileocecal valve. It is secondarily retroperitoneal, although it has its own mesentery in approximately 25% of patients and is 15 cm in length 1,2.
Ascites (hydroperitoneum is a rare synonym) is defined as an abnormal amount of intraperitoneal fluid.
Ascites (plural is same word) tends to be reserved for relatively sizable amounts of peritoneal fluid. The amount has not been defined formally, however it is noted that physiolog...
Ascitic fluid cholesterol level estimation is a simple and precise test for differentiating malignant ascites from non-malignant (cirrhotic) ascites 5-9.
Ascites is the abnormal collection of fluid within the peritoneal cavity. Malignant ascites comprises ~10% and is usually seconda...
Aspiration occurs if liquid or solid material enters the subglottic lower respiratory tract.
The term aspiration is used if material passes below the level of the vocal folds, i.e. subglottic. If material enters the larynx but remains above the vocal folds this is called penetratio...
Aspiration bronchiolitis, or diffuse aspiration bronchiolitis, is a condition characterized by a chronic inflammation of bronchioles caused by recurrent aspiration of foreign particles.
neurologic disorders: ~ 50% 3
dementia: ~50% 3
Patients with esop...
Asplenia refers to absence of the spleen thereby leading to deficient splenic function.
Seen in 3% of neonates with structural heart disease and in 30% of patients who die from cardiac malposition. The male-to-female ratio is 2:1.
Asplenia can be classified into two t...
Atresia (plural: atresias) refers to a situation where there is absence, underdevelopment or abnormal closure, of a normal anatomical tubular structure or opening.
Contrast this with agenesis which refers to the complete absence of any anatomical structure including its primordial precursors.
Atrio-esophageal fistulas are rare pathological connections between the left atrium and the esophagus.
The presentation is non-specific. Patients may complain of fever, malaise, and/or dysphagia, or present with neurological symptoms 3.
The chief cause of at...
Atrophic gastritis is a chronic condition of autoimmune and non-autoimmune etiology.
Two types of atrophic gastritis have been described 1-3:
type A: autoimmune
gastric body and fundus atrophy secondary to antiparietal cell antibodies
decreased secretion of acid and intrinsic fac...
Autoimmune pancreatitis (AIP) is a form of chronic pancreatitis associated with autoimmune manifestations on clinical, histological, and laboratory grounds 1.
Distinguishing this entity from other forms of chronic pancreatitis (such as alcohol-induced) is important as steroid treatment is effec...
Autosplenectomy denotes spontaneous infarction of the spleen with resulting hyposplenism.
Autosplenectomy is most frequently encountered in patients with homozygous sickle cell disease, although it has also been reported in pneumococcal septicemia 1, and systemic lupus erythematos...
Backwash ileitis is seen in patients with ulcerative colitis (UC), where the entire colon is involved. In such cases the terminal ileum is edematous.
Backwash ileitis extends contiguously backward from the cecum without skip regions. One source estimates it to occur in 6% of patients with UC, a...
The ball of wool sign, also referred to as the yarn sign or congealed water lily sign, is an ultrasound appearance, representing degeneration of hydatid cysts (WHO class CE 4). The inner side of the cyst detaches from the cyst wall and folds on itself, causing a change from anechoic (fluid) to a...
Balloon-occluded retrograde transvenous obliteration (BRTO) is a technique used by interventional radiologists in the treatment of gastric varices, particularly those with prominent infra-diaphragmatic portosystemic venous shunts (e.g. gastro-renal and gastro-caval shunts).
The technique is mor...
The Balthazar score is a subscore within the CT severity index (CTSI) for grading of acute pancreatitis.
The CTSI sums two scores:
Balthazar score: grading of pancreatitis (A-E)
grading the extent of pancreatic necrosis
The Balthazar score was originally used alone, but the addition of a sc...
Bannayan–Riley–Ruvalcaba syndrome (BRRS or BRR syndrome) is a very rare autosomal dominant hamartomatous disorder caused by a mutation in the PTEN gene. It is considered in the family of hamartomatous polyposis syndrome.
There are no formal diagnostic criteria for this disease, but characterist...
Bariatric embolization is an interventional procedure performed with a view to inducing weight-loss in the treatment of obesity. Evidence from clinical trials suggests that the procedure is well tolerated and has a good safety profile. Early studies demonstrate a mild-moderate beneficial effect....
Bariatric intragastric balloon therapy is a known therapy for weight loss, which involves a balloon being endoscopically-placed or swallowed and inflated inside the lumen of the stomach. The balloon resides in the stomach and the mechanism of action is presumably due to stretching the stomach, i...
Barium intravasation represents the feared - and fortunately very rare - complication of passage of barium sulfate contrast medium from the GI tract into the bloodstream.
Entry of barium into the bloodstream, usually the venous circulation is very rare, and a paper published in 20...
Barium peritonitis is a rare complication of gastrointestinal barium studies, and occurs when there is gastrointestinal tract perforation and spillage of barium contrast agent into the peritoneal cavity resulting in peritonitis, granuloma and stone formation 1.
Barium sulfate in the ...
Barium studies of the small intestine are still considered an effective modality to show the bowel loops in a cost-effective way.
Small bowel follow through (SBFT) or transit study
routine investigation for delineation of all parts the small bowel
done with barium meal after havin...
Barium sulfate (BaSO4), often just called barium in radiology parlance, is an ionic salt of barium (Ba), a metallic chemical element with atomic number 56. Barium sulfate forms the basis for a range of contrast media used in fluoroscopic examinations of the gastrointestinal tract. Unlike barium ...
Barium swallow is a dedicated test of the pharynx, esophagus, and proximal stomach, and may be performed as a single or double contrast study. The study is often "modified" to suit the history and symptoms of the individual patient, but it is often useful to evaluate the entire pathway from the ...
A barolith consists of inspissated barium sulfate associated with feces seen rarely, after barium studies for imaging the gastrointestinal tract. Since barium sulfate is insoluble, it can in rare cases precipitate in the bowel, sometimes becoming symptomatic with a significant delay (from few we...
Barrett esophagus is a term for intestinal metaplasia of the esophagus. It is considered the precursor lesion for esophageal adenocarcinoma.
Barrett esophagus is thought to have a prevalence of 3-15% in patients with reflux esophagitis. Mean age at diagnosis is 55 years old 5. Ris...
Beak sign in pyloric stenosis is one of the fluoroscopic (barium meal) findings which is useful in the diagnosis of congenital hypertrophic pyloric stenosis.
A beak-like tapering projection of barium is seen entering into the narrowed and compressed pyloric c...
Behçet disease is a multisystemic and chronic inflammatory vasculitis of unknown etiology.
The mean age at which Behçet disease occurs is 20-30 years. The disease is most prevalent in the Mediterranean region, Middle East and East Asia. The highest incidence has been reported in T...
Benign esophageal lesions are less symptomatic than malignant esophageal lesions, making up for only 1% of clinically apparent esophageal lesions.
esophageal leiomyoma (>50%)
esophageal fibrovascular polyp (~12.5%)
may contain fat
esophageal duplication cyst (10%)
Benign post-traumatic pseudopneumoperitoneum is the presence of ectopic gas typically between the 5th-10th intercostal spaces after high-energy trauma in the absence of other causes of pseudopneumoperitoneum such as pneumomediastinum 9.
Occurs with an incidence of 5% post-trauma...
The Bethesda criteria are an alternative to the Amsterdam criteria for the clinical diagnosis of hereditary non-polyposis colorectal cancer (HNPCC).
Diagnosis of HNPCC is made if any of the following criteria are fulfilled:
Amsterdam criteria are met
2 or more HNPCC related malignancies
Bezoars are accumulations of indigestible contents within the gastrointestinal tract 2.
There are several types depending on the predominant components:
trichobezoar: a bezoar formed from hair, this has also been called Rapunzel syndrome when the tail of the trichobezoar extends so...
Bilateral adrenal gland hyperenhancement or intense adrenal enhancement may be a feature of hypotension and forms part of the CT hypoperfusion complex.
Adrenal gland hyperenhancement has been described in pediatric and small adult series or individual cases of hemorrhagic shock, pancreatitis, s...
Biliary cast syndrome is a complication that occurs after liver transplantation, where dark solid bilirubin casts develop in the biliary tree, causing biliary obstruction.
This should be differentiated from biliary sludge, which represents thickened bile that has not precipitated.
Biliopancreatic diversion was a development on the jejunoileal bypass type of bariatric surgery. It can be performed with or without a duodenal switch.
The procedure involves
distal gastrectomy, with the formation of a gastric pouch
gastroenterostomy, with the formation of a ~250 cm Roux limb...
Billroth II gastrojejunostomy is a procedure that has been performed for tumor or severe ulcer disease in the distal stomach.
There are many variations on the procedure, but they generally involve resection of the diseased portion of the distal stomach and a side-to-side anastomosis of the resi...
Billroth I is a type of surgical reconstruction that has been performed after partial gastrectomy, usually in the setting of tumor or ulcer resection.
The key feature of a Billroth I reconstruction is the formation of an end-to-end anastomosis between the proximal remnant stomach and duodenal s...
The bird's beak sign of the esophagus is used to refer to the tapering of the inferior esophagus in achalasia. The same appearance (although it is difficult to see the similarity) is also referred to as the rat-tail sign.
The appearance, although classically occurring in primary achalasia, can ...
The bird beak sign of the right colon is tapering obstruction of the inferior part of right colon seen on contrast enema or CT scan with rectal contrast indicating cecal volvulus.
This sign can help to differentiate cecal volvulus from cecal bascule, in particular on a contrast/barium enema stu...
Bird's beak sign of the sigmoid is one of the signs of sigmoid volvulus. It represents gradual narrowing/tapering of the sigmoid colon up to the level of obstruction during contrast/barium insertion to the rectum or on CT.
When located in the sigmoid colon, it suggests the diagnosis of sigmoid ...
Blind loop syndrome (or "blind pouch syndrome") is an event that may occur after an end-to-end or end-to-side bowel anastomosis. Dilatation and stasis of the bypassed bowel may lead to bacterial overgrowth, breakdown of bile salts, and result in nutritional problems. It may even eventually lead ...
A helpful mnemonic for remembering the features of a Bochdalek hernia is:
B: back and lateral, usually on the left side
B: bad (associated with pulmonary hypoplasia)
To remember the side in which a Bochdalek hernia more commonly occurs (and to co...
Body imaging is the term assigned to cross-sectional imaging of the body, which radiologically refers to the chest, abdomen and pelvis. It is often used by radiologists who report this region (sometimes known as body imagers/radiologists) to differentiate their primary area of interest from othe...
Body packing refers to the internal concealment of drugs within the gastrointestinal tract or other orifices. People who do this may be called body packers, (drug) mules, stuffers, couriers or swallowers. Drugs may be concealed within condoms, foil, latex or cellophane.
There is ...
Boerhaave syndrome refers to an esophageal rupture secondary to forceful vomiting and retching.
It tends to be more prevalent in males, with alcoholism a risk factor. The estimated incidence is ~ 1:6000.
They are often associated with the clinical triad (Ma...
Borchardt's triad comprises of the classic three symptoms diagnostic of gastric volvulus 1:
severe sudden epigastric pain
intractable retching without vomiting
inability to pass a nasogastric tube
Bouveret syndrome refers to a gastric outlet obstruction secondary to impaction of a gallstone in the pylorus or proximal duodenum. Thus, it can be considered a very proximal form of gallstone ileus.
Bouveret syndrome occurs most commonly in elderly women. The presenting...
Bowel and mesenteric trauma can result from blunt force, penetrating and iatrogenic trauma.
The bowel and mesentery are injured in ~2.5% (range 0.3-5%) of blunt force abdominal trauma 1,3,5,8. However not surprisingly, bowel and mesenteric injuries are more frequent after penetrat...
This is a basic article for medical students and other non-radiologists
Bowel dilatation is a relatively non-specific sign than can be seen on most imaging modalities. In bowel obstruction, dilatation may be demonstrated on a plain radiograph providing the bowel is filled with gas.
Bowel obstructions are common and account for 20% of admissions with "surgical abdomens". Radiology is important in confirming the diagnosis and identifying the underlying cause.
Bowel obstructions are usually divided according to where the obstruction occurs, and since imaging appearances, und...
Bowel perforation, either small bowel perforation or large bowel perforation, can occur in many different settings, but the more common are
bowel obstruction (both small and large)
severe ulcer disease
This is a basic article for medical students and other non-radiologists
Bowel perforation is an acute surgical emergency where there is a release of gastric or intestinal contents into the peritoneal space.
This is a summary article; read more in our article on bowel perfora...
A mnemonic to remember causes of bowel sacculation is:
C: Crohn disease
Bowel wall thickening is a useful finding on imaging studies and has a number of different causes.
The reason for bowel wall thickening depends on the underlying etiology but includes submucosal edema, hemorrhage, and neoplastic infiltration.
In describing bow...
The B ring is a mucosal ring that develops in the distal esophagus at the gastroesophageal junction (Z line).
If the ring becomes symptomatic, then it is usually termed a Schatzki ring, although some use the terms synonymously.
Its development is thought to be a reacti...
Broad ligament hernias (alternative plural: herniae) are a type of internal hernia in which small bowel passes through a congenital or acquired defect in the broad ligament.
Broad ligament herniation is very rare and accounts for 4%-7% of all internal hernias 1.
Bronchogenic cysts and esophageal duplication cysts are embryological foregut duplication cysts and are also differential diagnoses for a cystic mediastinal mass.
asymptomatic bronchogenic cyst
symptomatic esophageal cyst in the case of peptic ulceration
Brunner gland adenomas are hyperplastic areas of the Brunner glands within the duodenum that are greater than 1 cm. They tend to be 1-2 cm in diameter, although case reports have described tumors of up to 12 cm diameter. Where the diameter of focal hyperplasia is less than 1 cm, the term Brunner...
Brunner gland hyperplasia results from disproportionate overgrowth of Brunner glands in the duodenum as a result of hyperacidity.
Hyperplasia begins at the pylorus and extends distally within the first 2/3rds of the duodenum. Where the focal growth of hyperplastic cells is greater than 1 cm in ...