The 3-6-9 rule is a simple aide-memoire describing the normal bowel caliber:
small bowel: <3 cm
large bowel: <6 cm
appendix: <6 mm
cecum: <9 cm
Above these dimensions, the bowel is generally considered dilated, and obstruction or an adynamic ileus should be considered.
4D syndrome is a term used to describe a manifestation of syndromic glucagonoma, a type of pancreatic endocrine tumor.
D: dermatitis 2
necrolytic migratory erythema - a widespread rash, tending to involve perioral and perigenital regions
oral rashes (angular stomatitis, cheilitis)
tend to re...
Aaron sign is a clinical sign that is defined as a feeling of distress and pain in the epigastric, umbilical and praecordial regions, on steady pressure over McBurney point, it is suggestive of chronic appendicitis.
History and etymology
Charles Dettie Aaron (1866–1951) was an American gastroe...
The American Association for the Surgery of Trauma (AAST) injury scoring scales are the most widely accepted and used system of classifying and categorizing traumatic injuries. Injury grade reflects severity, guides management, and aids in prognosis. Currently (early 2019), 32 different injury s...
The American Association for the Surgery of Trauma (AAST) splenic injury scale, most recently revised in 2018, is currently the most widely used grading system for splenic trauma.
The 2018 update incorporates "vascular injury" (i.e. pseudoaneurysm, arteriovenous fistula) into the imaging criter...
The AP supine abdominal radiograph can be performed as a standalone projection or as part of an acute abdominal series, depending on the clinical question posed, local protocol and the availability of other imaging modalities.
This view is useful in assessing abdominal pathologies,...
The dorsal decubitus view is a supplementary projection often replacing the lateral decubitus view in the context of an unstable patient who is unable to roll nor stand. Used to identify free intraperitoneal gas (pneumoperitoneum). It can be performed when the patient is unable to be transferred...
The lateral decubitus abdominal radiograph is used to identify free intraperitoneal gas (pneumoperitoneum). It can be performed when the patient is unable to be transferred to, or other imaging modalities (e.g. CT) are not available. The most useful position for detecting free intraperitoneal ai...
AP oblique supine radiograph is a projection often used in barium studies and foreign body localization.
This view is normally performed when localizing foreign bodies or lines within the abdominal cavity. Additionally, the oblique abdominal series can be utilized in the assessment...
The PA erect abdominal radiograph is often obtained in conjunction with the AP supine abdominal view in the acute abdominal series of radiographs.
The erect abdominal radiograph has virtually disappeared from clinical practice in the United Kingdom, with studies dating back to the 1980s affirmi...
The PA prone radiograph is rarely performed and is often utilized when a patient is unable to lay supine. The projection is adequate for the examination of the abdominal cavity, however, not as practical for the renal structures due to magnification.
This view is useful in visualiz...
The CT abdomen-pelvis protocol serves as an outline for an examination of the whole abdomen including the pelvis. It is one of the most common CT protocols for any clinical questions related to the abdomen and/or in routine and emergencies. It forms also an integral part of trauma and oncologic ...
The abdomen radiograph is a commonly requested examination in the pediatric patient. Children that present for abdominal x-rays are often very unwell, therefore specialized techniques and appropriate communication are essential for gaining the child's cooperation.
Abdominal adhesions are bands of scar tissue (ﬁbrous or ﬁbrofatty), most often occurring as a complication of previous abdominal surgery.
Adhesions often occur with
multiple abdominal operations or previous postoperative intra-abdominal complications
history of intra-abdominal inﬂa...
Abdominal and pelvic anatomy encompasses the anatomy of all structures of the abdominal and pelvic cavities.
This anatomy section promotes the use of the Terminologia Anatomica, the international standard of anatomical nomenclature.
The abdominal cavity is divided into two major compartments, the peritoneum and retroperitoneum, early in fetal development.
The parietal peritoneum is reflected over the peritoneal organs to form a series of supporting peritoneal ligaments, mesenteries and omenta. The peritoneal reflections ca...
Abdominal compartment syndrome (ACS) is a disease defined by the presence of new end-organ dysfunction secondary to elevated intraabdominal pressure (IAP). Radiological diagnosis is difficult and usually suggested when a collection of imaging findings are present in the appropriate clinical sett...
A mnemonic for causes of abdominal distension (6 Fs) is:
F: fulminant mass
Abdominal hernias (herniae also used) may be congenital or acquired and come with varying eponyms. They are distinguished primarily based on location and content. 75-80% of all hernias are inguinal.
Content of the hernia is variable, and may include:
small bowel loops
mobile colon segments (s...
The lateral view abdominal radiograph is a less common projection of the abdomen, it is different from the lateral decubitus view of the abdomen and looks more like a lateral lumbar spine view.
This projection is often requested as a useful problem-solving view that can complement ...
Abdominal migraine is a syndrome that presents as recurrent episodes of severe paroxysmal abdominal pain, coupled with vasomotor symptoms, nausea, and emesis that lasts for at least 1 hour 3. Historically it has tended to be a pediatric diagnosis, but it is now increasingly seen in adults. It is...
An opacity projecting over the abdomen has a broad differential. Possibilities to consider include:
ingested, e.g. coins, batteries, bones, etc
artifacts, e.g. object attached to the cloth of the patient like a safety pin or button
iatrogenic, e.g. hemostatic clips, gastric ba...
This mnemonic helps to remember the relative echogenicity of abdominal organs on ultrasound:
Darling Parents So Love Kids
From most to least echogenic:
K: kidneys (cortex)
The abdominal pain in pregnancy MRI protocol encompasses a set of MRI sequences for assessment of causes of non-traumatic abdominal pain in pregnancy.
Note: This article aims to frame a general concept of an MRI protocol for the assessment of the abdomen in pregnancy. Protocol specifics will va...
An abdominal paracentesis (plural: paracenteses), more commonly referred to as an ascitic tap, is a procedure that can be performed to collect peritoneal fluid for analysis or as a therapeutic intervention.
diagnostic: especially for newly-diagnosed ascites
determine etiology of a...
A mnemonic to remember the contraindications to abdominal paracentesis is:
C: coagulopathy (INR >2.0)
A: abdominal wall cellulitis
S: surgical abdomen (absolute contraindication) / severe thrombocytopenia (platelet count <50 x 103/μL)
I: intra-abdominal adhes...
Abdominal radiography can be useful in many settings. Before the advent of computed tomography (CT) imaging, it was a primary means of investigating gastrointestinal pathology and often allowed indirect evaluation of other abdominal viscera.
Although abdominal radiography has lower...
This is a basic article for medical students and other non-radiologists
Abdominal radiology curriculum for medical students is broadly split into content that refers to imaging (the test and findings) and conditions that are considered key for this stage of training.
Some non-abdominal conditi...
Abdominal surface anatomy can be described when viewed from in front of the abdomen in 2 ways:
divided into 9 regions by two vertical and two horizontal imaginary planes
divided into 4 quadrants by single vertical and horizontal imaginary planes
These regions and quadrants are of clinical imp...
Abdominal trauma is usually divided into blunt and penetrating trauma.
Findings of abdominal trauma
splenic trauma: most common
gastrointestinal tract (bowel) trauma:
proximal jejunum is most commonly affected by blunt trauma,...
Abdominal tuberculous can manifest in almost every abdominopelvic organ:
jejunal and ileal tuberculosis
Abdominal x-ray review is a key competency for medical students, junior doctors and other allied health professionals. Using ABDO X is a helpful and systematic method for abdominal x-ray review, where D refers to the assessment of dense structures such as the bones and areas of calcification.
Abdominal x-ray review is a key competency for medical students, junior doctors and other allied health professionals. Using ABDO X is a helpful and systematic method for abdominal x-ray review:
A: air - where it should and shouldn't be
B: bowel - position, size and wall thickness
D: dense st...
Abdominal x-ray review is a key competency for medical students, junior doctors and other allied health professionals. Using ABDO X is a helpful and systematic method for abdominal x-ray review, where A refers to the assessment of the presence and location of air.
Abdominal x-ray review is a key competency for medical students, junior doctors and other allied health professionals. Using ABDO X is a helpful and systematic method for abdominal x-ray review, where X refers to the assessment of external objects and artifacts.
Abdominal x-ray review is a key competency for medical students, junior doctors and other allied health professionals. Using ABDO X is a helpful and systematic method for abdominal x-ray review, where B refers to the assessment of the bowel loops.
stomach, small bowel and...
Abdominal x-ray review is a key competency for medical students, junior doctors and other allied health professionals. Using ABDO X is a helpful and systematic method for abdominal x-ray review, where O refers to the assessment of the intra-abdominal organs and soft tissues.
This is a basic article for medical students and other non-radiologists
Abdominal radiographs can be a useful examination, but you need to think about the question you are asking before getting the test. Before the advent of computerized tomography (CT) imaging, it was a primary means of invest...
Abnormal bowel wall attenuation patterns on CT scan can be grouped under five categories:
water halo sign
fat halo sign
The first three patterns are seen on contrast studies.
It is defined as uniform enhancement of th...
A mnemonic used for abnormal collection of barium anywhere in the body:
Abnormal intra-abdominal gas is an important radiologic finding with many potential causes. It may be seen on a chest radiograph, abdominal radiograph, CT or MRI.
abnormally located bowel, e.g. Chilaiditi syndrome (bowel interpose...
Abscesses are focal confined collections of suppurative inflammatory material and can be thought of as having three components 1:
a central core consisting of necrotic inflammatory cells and local tissue
peripheral halo of viable neutrophils
surrounded by a 'capsule' with dilated blood vessel...
The accessory appendicular artery, also known as the artery of Seshachalam, is a branch of the posterior cecal artery. It arises from the ileocolic artery, and runs in the mesoappendix.
The exact prevalence of this accessory artery and its impact upon the risk of appendicitis varies among studi...
The accordion sign (also known as concertina sign) is seen on CT of the abdomen and refers to the similarity between the thickened edematous wall of pseudomembranous colitis and the folds of an accordion. This appearance is the result of hyperemic enhancing mucosa stretched over markedly thicken...
Achalasia (primary achalasia) is a failure of organized esophageal peristalsis causing impaired relaxation of the lower esophageal sphincter, and resulting in food stasis and often marked dilatation of the esophagus.
Obstruction of the distal esophagus from other non-functional etiologies, not...
Pancreatic acinar cell carcinoma is a rare exocrine neoplasm that comprises ~1% of all pancreatic tumors. This tumor shows more aggressive behavior than the far more common adenocarcinoma 1,3,4.
High levels of serum lipase, due to hypersecretion syndrome, resulting in sub...
An acquired tracheo-esophageal fistula refers to a pathological communication between the trachea and esophagus due to a secondary cause.
Acquired causes of tracheo-esophageal fistulae can be divided into those that are related to malignancy (common) and those from other causes (unco...
Acute abdominal pain is a common acute presentation in clinical practice. It encompasses a very broad range of possible etiologies and diagnoses, and imaging is routinely employed as the primary investigative tool in its modern management.
A subgroup of patients with acute abdomina...
The acute abdominal series is a common set of abdominal radiographs obtained to evaluate bowel gas.
The acute series is used for a variety of indications including:
determine the amount of bowel gas, with possible bowel distention
assess air-fluid levels
Acute appendicitis (plural: appendicitides) is an acute 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.
This is a basic article for medical students and other non-radiologists
Acute cholecystitis refers to the acute inflammation of the gallbladder. It is the primary complication of cholelithiasis and the most common cause of acute pain in the right upper quadrant (RUQ).
Acute gastritis is a broad term that encompasses a myriad of causes of gastric mucosal inflammation.
It depends on the etiology (see below).
nausea and vomiting
loss of appetite
Acute mesenteric ischemia accounts for the majority (around 95%) of cases with mesenteric ischemia and comprises of:
arterial occlusive mesenteric ischemia (60-85%)
embolic acute mesenteric ischemia (EAMI)
thrombotic acute mesenteric ischemia (TAMI)
non-occlusive mesenteric ischemia (NOMI) (...
Acute necrotic collections (ANCs) are an early, local complication of necrotizing pancreatitis.
The following are the latest terms according to the updated Atlanta classification to describe fluid collections associated with acute pancreatitis 1,2:
fluid collections in interstitia...
Acute non-traumatic abdominal pain in pregnancy requires a considered imaging approach due to the increased risks of fetal demise associated with undiagnosed diseases such as perforated acute appendicitis. Ultrasound is the first-line modality due to its wide availability and ability to diagnose...
Acute pancreatitis (plural: pancreatitides) is an acute inflammation of the pancreas and is a potentially life-threatening condition.
There are two subtypes of acute pancreatitis as described by the Revised Atlanta Classification 1:
interstitial edematous pancreatitis
A mnemonic to remember the severity criteria for acute pancreatitis is:
P: PAO2 <8 kpA
A: age >55 years
N: neutrophilia (WBC >15 x 109 / L)
C: calcium <2 mmol/L
R: renal (urea >16 mmol/L)
E: enzymes (LDH >600 IU/L and AST >200 IU/L)
A: albumin (serum) <32 g/L
This is a basic article for medical students and other non-radiologists
Acute pancreatitis refers to acute inflammation of the pancreas and is a potentially life-threatening condition.
This is a summary article; read more in our article on acute pancreatitis.
Acute peripancreatic fluid collections (APFC) are an early complication of acute pancreatitis that usually develop in the first four weeks. After four weeks, the term pseudocysts is used. The absence of necrosis differentiates APFCs from acute necrotic collections (ANC), that is, APFCs occur in ...
Acute phlegmonous esophagitis is a very rare form of esophagitis in which there is a diffuse bacterial infection within the submucosa of the esophagus 1.
Usually there is co-infection of the stomach (phlegmonous gastritis), and if both the stomach and esophagus are involved it is c...
Adenocarcinoma of the appendix, also referred to as nonmucinous adenocarcinoma of the appendix, is an uncommon type of appendiceal epithelial neoplasm. Different from the appendiceal mucinous neoplasms, these tumors share similar epidemiology and pathology with colorectal adenocarcinoma.
Primary adenocarcinoma of the small bowel is about 50 times less common than colonic carcinoma.
Almost 50% of small bowel adenocarcinomas are found in the duodenum, especially near the ampulla. In the remaining cases, the jejunum is more commonly involved than the ileum1.
Adenomyomatosis of the gallbladder is a hyperplastic cholecystosis of the gallbladder wall. It is a relatively common and benign cause of diffuse or focal gallbladder wall thickening, most easily seen on ultrasound and MRI.
Adenomyomatosis is relatively common, found in ~9% of al...
An adrenal lipoma is an extremely rare macroscopic fat-containing adrenal lesion, with only a handful of cases described in the literature 1.
Like other lipomas elsewhere in the body, they are benign tumors of mesenchymal origin that contain mature fatty tissue and are surrounded by ...
Adrenal metastases are the most common malignant lesions involving the adrenal gland. Metastases are usually bilateral but may also be unilateral. Unilateral involvement is more prevalent on the left side (ratio of 1.5:1).
They are present at autopsy in up to 27% of patients with ...
An adrenal teraoma is a very rare adrenal lesion. They account for around 0.7% of all primary adrenal tumors. As with teratomas in general, they are composed of mature tissues arising from more than one germinal layer.
They classically demonstrate a large fatty/lipomatous...
Adrenal washout can be calculated using the density value of an adrenal mass on non-enhanced, portal venous phase and 15 minutes delayed CT scans (density measured in Hounsfield units (HU)). It is primarily used to diagnose adrenal adenoma.
[(HUportal venous phase) - (HUdelaye...
Adynamic ileus is the failure of passage of enteric contents through the small bowel and colon that are not mechanically obstructed; i.e. it represents a paralysis of intestinal motility.
Patients may be asymptomatic or present with symptoms similar to mechanical bowel ob...
A mnemonic for the common causes of adynamic ileus is:
The classic "5 Ps" are:
P: potassium: low (also disturbances of other electrolytes)
P: pelvic and spinal fractures
However, there are a few further Ps that can be included...
The aerodigestive tract is a non-TA descriptive collective term for the respiratory tract and proximal portion of the digestive tract. As it is a non-standard term, its precise components vary somewhat with the context in which the term is being employed.
Definitions of what precis...
Afferent loop syndrome is an intermittent partial or complete mechanical obstruction of the afferent limb of a gastrojejunostomy.
The syndrome classically refers to obstruction of the upstream limb of a side-to-side gastrojejunostomy but has also been used to refer to the biliopancreatic limb o...
Agenesis of the appendix is extremely rare, with an incidence at surgery of approximately 1 in 100,000 laparotomies 1. It is most commonly due to a sporadic etiology. However in the rare genetic condition, familial apple peel jejunal atresia, absence of the appendix is a recognized feature. Also...
AIDS-defining illnesses are conditions that in the setting of a HIV infection confirm the diagnosis of AIDS and do not commonly occur in immunocompetent individuals 2. According to the CDC surveillance case definition 1, they are:
bacterial infections: multiple or recurrent
Allgrove syndrome (also known as triple A syndrome) is an autosomal recessive condition that consists of three main findings:
Alpers syndrome, also known as Alpers-Huttenlocher syndrome or progressive cerebral poliodystrophy, is a rare childhood neurodegenerative POLG-related disorder. Along with Leigh syndrome, it is one of the commonest childhood mitochondrial disorders 1.
Alpers syndrome is incredibl...
Alpha-fetoprotein (AFP) is an important plasma protein synthesized by the yolk sac and fetal liver. In adults, its main utility is as a tumor marker, primarily for hepatocellular carcinoma or teratoma. Functionally it is the fetal homologue of albumin i.e. it acts as a major carrier protein in t...
The Alvarado score is a clinical decision rule and predictor of the likelihood of acute appendicitis.
right lower quadrant tenderness (+2)
elevated temperature (37.3°C or 99.1°F) (+1)
rebound tenderness (+1)
migration of pain to the right lower quadrant (+1)
Amoebic colitis is a type of infectious colitis, more common in tropical and subtropical areas. The causative agent is the trophozoite form of the protozoan Entamoeba histolytica. In most cases of transmission, the cyst form lives in the colon as a commensal and patients remain asymptomatic.
Ampulla (plural: ampullae) is an anatomical term used for tubular structures with a short segmental bulbous dilatation:
ampulla (fallopian tube)
ampulla (lacrimal system)
ampulla (semicircular ducts)
ampulla of Vater
ampulla (ductus d...
The ampulla of Vater is a conical structure at the confluence of the common bile duct (CBD) and the main pancreatic duct that protrudes at the major duodenal papilla into the medial aspect of the descending duodenum. The entire structure is encased by smooth muscle fibers that compose the sphinc...
The term ampullary tumor generally refers to either benign or malignant neoplasms that arise from the glandular epithelium of the ampulla of Vater, including 1:
ampullary adenoma (adenoma of ampulla of Vater)
ampullary carcinoma (carcinoma of ampulla of Vater)
According to some authors, ampul...
The Amsterdam criteria are used in the diagnosis hereditary non polyposis colorectal cancer (HNPCC).
Amsterdam Criteria I
Initial description in 1991:
> or equal to 3 relatives with colorectal cancer (CRC)
> or equal to 1 case in a first degree relative
> or equal to 2 successive generation...
Amyand hernias (alternative plural: herniae) are a rare form of inguinal hernia in which the vermiform appendix is located within the hernial sac. They are seen in less than 1% of inguinal hernias.
It should not be confused with an appendix-containing femoral hernia, known as a De Garengeot he...
Amylase is widely employed as a marker of acute pancreatitis and a significant elevation is diagnostic.
α-amylase is a digestive enzyme that is predominantly secreted by the acinar cells of the exocrine pancreas. It is also secreted by the salivary glands. Pancreatic amylase is enco...
Anal atresia, or imperforate anus, refers to a spectrum of anorectal abnormalities ranging from a membranous separation to complete absence of the anus.
The estimated incidence is 1 in 5000 live births.
Clinically there is no anal opening. Subtypes can be classified in...
The anal canal is the terminal part of the gastrointestinal tract, whilst the anus (plural: anuses or ani) specifically refers to the opening separating the anal canal from the outside, at the distal most aspect of the anal verge. Anatomically, the anal canal is referred to as the terminal alime...
MRI protocol for anal canal cancer is a group of MRI sequences put together to asses extension and stage anal canal tumors.
Note: This article is intended to outline some general principles of protocol design. The specifics will vary depending on MRI hardware and software, radiologist's and ref...
Anal cancer is relatively uncommon, accounting for less than 2% of large bowel malignancies. Most cases are squamous cell carcinoma on histology.
It accounts for less than 2% of large bowel malignancies and 1-6% of anorectal tumors (~1.5% of all gastrointestinal tract malignancies...
The most recent version of TNM staging of anal cancer is as follows:
Primary tumor (T)
TX: primary tumor cannot be assessed
T0: no evidence of primary tumor
Tis: carcinoma in situ (Bowen disease, high-grade squamous intraepithelial lesion [HSIL], anal intraepithelial neoplasia II-III (AIN II...
Anal margin or perianal skin is arbitrarily defined as a skin tissue with a radius of 5 cm from the anal verge, consisting of keratinizing squamous epithelial tissue containing hair follicles. A radius of 5 cm approximately equates to a circle of area of 78.5 cm2 centered on the anal verge.
The anal sphincter is divided into internal and external anal sphincters. It surrounds the anal canal.
Internal anal sphincter
continuation of inner rectal muscle
thickened, circular muscle fibers, up to 5 mm thick
composed of visceral muscle
External anal sphincter
The anal triangle forms the posterior half of the diamond-shaped perineum. The triangle's three corners are defined by the tip of the coccyx posteriorly and both ischial tuberosities anterolaterally. The anterior border is the transverse perineal muscles and the posterolateral borders are the sa...
The anal verge is part of the anal region and consists of a band of squamous epithelial tissue which lacks hair follicles and extends from the inter-sphincteric groove to the perianal skin.