The large intestine (or large bowel) is a 1.5 metre muscular tube that extends from the caecum to the rectum. It has three outer longitudinal muscular layers called taenia coli, which are about 30 cm shorter than the length of the large bowel causing characteristic sacculations interrupted by in...
The lateral crescent sign is a useful diagnostic sign of a direct inguinal hernia on CT scan, the hernia causing compression and lateral displacement of the inguinal canal contents (ductus deferens, testicular vessels, fat, etc.) to form a semicircle of tissue that resembles a moon crescent seen...
The lateral fossae are concave depressions of peritoneum in the paravesical space that lie between the lateral umbilical folds and the lateral parietal peritoneum. The lateral fossae are the smallest of the anterior paravesical fossae, and typically partially contain the cecum and/or sigmoid col...
The lateral umbilical folds are raised ridges of parietal peritoneum in the deep aspect of the anterior abdominal wall overlying the inferior epigastric vessels. The paired folds originate medial to the deep inguinal ring and end at the arcuate line on the posterior aspect of the anterior abdomi...
The lead pipe appearance of colon is the classical barium enema finding in chronic ulcerative colitis. There is complete loss of haustral markings in the diseased section of colon, and the organ appears smooth-walled and cylindrical.
The left colic artery is the first branch of the inferior mesenteric artery.
It ascends retroperitoneally, dividing into two branches:
passes anteriorly to the left kidney, then enters the
transverse mesocolon, and passes superiorly to supply the upper part of the...
Left colic flexure (or splenic flexure) is the bend in the large intestine in the left upper quadrant of the abdomen as the transverse colon continues as the descending colon. The phrenicocolic ligament attaches the the splenic flexure to the left hemidiaphragm. It lies more cranial than the rig...
The left gastric artery is the smallest and first branch of the coeliac artery.
It passes superiorly, giving off an oesophageal branch to the distal oesophagus, then enters the lesser omentum to pass along the lesser curvature of the stomach. Anastomoses along the lesser curvature with the r...
The left gastric vein (also known as the coronary vein) drains both gastric walls. It forms a loop with the right gastric vein at the lesser curvature of the stomach. The left gastric vein travels in the lesser omentum to drain in the portal vein. It also communicates with the lower oesophageal ...
The left gastroepiploic artery (LGA) is one of the branches of the splenic artery.
The LGA runs within the two layers of the greater omentum to the right along the greater curvature of the stomach, approximately 1 cm from the gastric wall before it anastomoses with the ri...
The left perihepatic space is a subdivision of the left supramesocolic space.
The left perihepatic space can be further subdivided into anterior and posterior spaces:
anterior perihepatic space
lies between the diaphragm and the anterosuperior aspect of the left lobe of the liv...
The left subphrenic space is a subcompartment of the supramesocolic space located between the diaphragm and the superior surface of the left lobe of liver.
It is described to have anterior and posterior parts without clear delineation1.
medially: falciform ligament
Leiomyosarcomas (LMS) are extremely rare malignant neoplasms that originate from smooth muscle cells and may be considered the malignant counterpart of a leiomyoma. They are classified as a soft tissue tumour and account for ~8% of malignant soft tissue tumours 10.
Lemmel syndrome is defined as an obstructive jaundice caused by a periampullary duodenal diverticulum (of the second part of the duodenum) compressing the intrapancreatic part of the common bile duct with resultant upstream dilatation of the extra- and intrahepatic bile ducts.
The lesser sac or omental bursa is a potential peritoneal space within abdomen, part of the peritoneal cavity. It may be conceptualized as the space posterior to the lesser omentum, between the posterior wall of the stomach and surface of peritoneum which covers the anterior surface of the left ...
Lesser sac hernias are a type of internal hernia, where abdominal contents protrude through the foramen of Winslow, hence they are also known as foramen of Winslow hernia.
Lesser sac hernias are rare, accounting for <0.1% of abdominal hernias and 8% of internal hernias 1,2.
The levator ani, also known as the muscular pelvic diaphragm, is the musculotendinous sheet that forms the majority of the pelvic floor, supports the pelvic viscera, and aids in urinary and faecal evacuation as well as maintaining continence.
The levator ani has three main compon...
Levator ani syndrome (LAS) is a musculoskeletal pain syndrome involving the pelvic floor, thought to be caused by spasm or scarring of the levator ani muscles.
Levator ani syndrome is characterised by recurrent pain, pressure or discomfort in the region of the rectum, sac...
Li-Fraumeni syndrome is a hereditary cancer syndrome due to mutations in the tumour suppressor gene TP53. Approximately half of affected individuals are thought to develop invasive cancer by 30 years of age 1.
The ligament of Treitz, also known as the suspensory ligament of the duodenum, is a double fold of peritoneum suspending the duodenojejunal flexure from the retroperitoneum.
It is often used interchangeably with duodenojejunal (DF) flexure.
The ligament of Treitz is comprised of two p...
The ligamentum venosum is a fibrous remnant which travels superiorly from porta hepatic of the liver to the inferior vena cava. It is often obliterated in adults.
In the fetus, it is patent and known as the ductus venosus which shunts blood returning from the placenta in the umbilical vein to ...
The light bulb sign of an adrenal phaeochromocytoma is MRI feature of this tumour. This refers to marked hyperintensity seen on T2 weighted sequences however this finding is neither sensitive nor specific and phaeochromocytomas are more often heterogeneous with intermediate or high T2 signal int...
The line alba (Latin for white line) is a single midline fibrous line in the anterior abdominal wall formed by the median fusion of the layers of the rectus sheath medial to the bilateral rectus abdominis muscles. It attaches to the xiphoid process of the sternum and the pubic symphysis. The umb...
Linitis plastica is a descriptive term usually referring to the appearance of the stomach, although the rectum can also be described this way. The appearance is said to be reminiscent of an old leather water-bottle.
The underlying cause is usually a scirrhous adenocarcinoma with diff...
Lipase, more specifically pancreatic lipase, is an enzyme produced in the pancreas and is responsible for the digestion of fat molecules. It may be raised in numerous pancreatic, hepatobilary and other diseases but is most commonly associated with acute pancreatitis.
Lipomas are benign tumours composed of mature adipocytes. They are the most common soft tissue tumour, seen in ~2% of the population.
Patients typically present in adulthood (5th-7th decades).
Typically lipomas are subcutaneous in location and present in a...
Lipomatosis is a condition where there is diffuse excessive fat deposition within the body. This can especially affect certain regions.
neck and upper region of trunk
lipomatous hypertrophy of the interatrial septum
lipomatous metaplasia of th...
Lipomatosis of the ileocaecal valve is a benign condition usually detected incidentally during investigation of other conditions. However, it may itself cause certain vague abdominal symptoms and may be missed on preliminary ultrasound unless a high level of suspicion is present.
Liposarcomas are malignant tumours of fatty tissue and are the malignant counterpart to a benign lipoma. They are the second commonest type of soft-tissue sarcoma.
Liposarcomas are typically found in adults, typically between the ages of 40 and 60, and are rare in children.
Littoral cell angioma of the spleen (LCA) is a rare and relatively recently (1991) described vascular tumour of the spleen.
Littoral cell angiomas may occur at any age and have no gender predilection.
Typically, patients with littoral cell angioma are found...
Littre hernia is a hernia containing a Meckel's diverticulum. Also known as a persistent omphalomesenteric duct hernia. It is most frequently encountered in the inguinal region.
blind ending tubular structure arising from antimesentric border of small bowel and extend...
The liver is the largest abdominal organ that plays a major role in metabolism and has a number of functions, including glycogen storage, decomposition of red blood cells, plasma protein synthesis, hormone production, and detoxification. It is one of the very few organs that has the ability to r...
The liver overlap sign can be seen in sigmoid volvulus wherein the sigmoid loop is seen, usually on an abdominal radiograph, ascending to the right upper quadrant and projecting over the liver shadow.
In one study of 21 patients with confirmed sigmoid volvulus, the sign was present in 9 patient...
The loop-to-loop colon describes an abnormal colonic course associated with the absence of the left kidney from the renal fossa.
The transverse colon extends to the lateral margin of the abdominal wall and the descending colon courses medially to fill the renal fossa, resulting in a "looped" c...
Low attenuation lymphadenopathy suggests underlying necrosis and can be seen in:
metastatic carcinoma (or lymphoma)
infections (tuberculous or fungal)
inflammatory necrotic disorders (e.g. Kikuchi-Fujimoto disease)
low attenuation ly...
Causes of calcifications in the lower abdomen and pelvis include:
seminal vesicle and ductus deferens calcification
dropped stones following chol...
Lower gastrointestinal bleeding (LGIB) is defined as that occurring distal to the ligament of Treitz (i.e. from the jejunum, ileum, colon, rectum or anus) and presenting as either haematochezia (bright red blood/clots or burgundy stools) or melaena.
The incidence of LGIB is only o...
Lower gastrointestinal bleeding usually occurs distal to the ligament of Treitz, and has a wide differential diagnosis:
Low-grade appendiceal mucinous neoplasms (LAMN), previously known as appendiceal mucinous cystadenomas, are rare mucinous tumours of the appendix showing low-grade cytologic atypia, c.f. high-grade appendiceal mucinous neoplasms.
Considerable controversy still exists on mucinous n...
The lucent liver sign is represented by a reduction of hepatic radiodensity on supine radiograph when there is a collection of free intraperitoneal gas located anterior to the liver.
Lumbar hernias are a rare form of posterior abdominal hernia.
Most common in patients aged between 50 and 70 years with a male predominance 1.
Patients with lumbar hernias can present with a variety of symptoms, including a posterolateral mass, back pain,...
Lymphocele of the thoracic duct (thoracic duct cyst) is usually asymptomatic or less commonly may present as left supraclavicular fossa mass 1.
The clinical significance of a thoracic duct cyst lies in its misidentification as a pathological lesion at radiological assessment, whi...
The term magenstrasse refers to a tubular portion of the stomach adjacent to the lesser curve of the stomach. It is a favoured route by food, fluids and drugs as they flow from the cardia/fundus to the gastric outlet 1.
Magenstrasse is an old German anatomical term that has come back into commo...
Magnetic resonance cholangiopancreatography (MRCP) is a non-invasive imaging technique to visualize intra and extrahepatic biliary tree and pancreatic ductal system.
It can provide the diagnostic range equivalent to the ERCP and so it can replace the ERCP in high risk patient to avoid significa...
This is a basic article for medical students and other non-radiologists
Malignant biliary tract obstruction (MBTO) represents a group of conditions that cause obstructive jaundice. While most examples are the result of pancreatic head cancers, other malignancies may be causative.
Malignant oesophageal neoplasms are much more common than benign oesophageal neoplasms, especially if the patient is symptomatic.
oesophageal carcinoma (90%)
oesophageal squamous cell carcinoma (SCC)
oesophageal spindle cell carcinoma
Barium meal has been frequently used to differentiate malignant and benign gastric ulcers:
Features suggesting benign gastric ulcer
outpouching of ulcer crater beyond the gastric contour (exoluminal)
smooth rounded and deep ulcer crater
smooth ulcer mound
smooth gastric folds that reach the...
Mallory-Weiss tears occur due to violent projection of gastric contents against the lower oesophagus, which results in mucosal and submucosal tear with involvement of the venous plexus. The resultant clinical syndrome is known as Mallory-Weiss syndrome.
Patients present ...
Malone antegrade continence enema is a surgical procedure where the vermiform appendix or ‘neoappendix’ is used to create a small stoma at the abdominal wall allowing antegrade enemas to be administered to empty the colorectum. This procedure is important particularly in children and adolescents...
The marginal artery of Drummond, also known as the marginal artery of the colon, is a continuous arterial circle or arcade along the inner border of the colon formed by the anastomoses of the terminal branches of the superior mesenteric artery (SMA) and inferior mesenteric artery (IMA).
Remembering the colon vascular supply can be confusing because of inconstant collateral vascularisation, therefore mnemonics can be helpful.
One way to remember the location of the marginal artery of Drummond is to remember that it runs distally to the root of the mesentery (near the colon).
Maydl hernias are defined as the presence of two small bowel loops within a single hernial sac, that is, there are two efferent and two afferent loops of bowel, forming a "W" shape.
This type of hernia is more prone to strangulation and necrosis. The intervening intra-abdominal loop is also at ...
McBurney point is defined as a point that lies one-third of distance laterally on a line drawn from the umbilicus to the right anterior superior iliac spine. Classically, it corresponds to the location of the base of the appendix 1.
Clinically, McBurney point is relevant for the elicitation of ...
The McKeown procedure ("tri-incisional oesophagectomy") is a type of oesophagectomy, that is similar in concept to an Ivor Lewis procedure, but it tends to be used for oesophageal lesions that are higher in the oesophagus.
stomach mobilized, the oesophagus
Meandering main pancreatic duct (MMPD) comprises of a reverse Z-type and loop-type of pancreatic ducts.
These ductal variants are found in ERCP and MRCP studies. The exact incidence is not known.
Increased incidence of meandering pancreatic duct has been reported in patients with idiopathic re...
Meckel diverticulitis is the inflammation of Meckel diverticulum, which is the most common congenital structural abnormality of the gastrointestinal tract 3. Despite this, it is an uncommon cause of acute abdomen and is often not correctly diagnosed pre-operatively.
This article focuses on Mec...
Meckel diverticulum is a congenital intestinal diverticulum due to fibrous degeneration of the umbilical end of the omphalomesenteric (vitelline) duct that occurs around the distal ileum. It is considered the most common structural congenital anomaly of the gastrointestinal tract.
Meconium ileus refers to a neonatal bowel obstruction of the distal ileum due to abnormally thick and impacted meconium. Unlike in the meconium plug syndrome, the meconium is abnormal in consistency.
Meconium ileus is more common in white populations and affects both sexes almost ...
Meconium peritonitis refers to a sterile chemical peritonitis due to intra-uterine bowel perforation and spillage of fetal meconium into the fetal peritoneal cavity. It is a common cause of peritoneal calcification.
The estimated prevalence is at ~1 in 35,000.
The medial fossae are concave depressions of peritoneum in the paravesical space bounded by the medial umbilical folds and the lateral umbilical folds. The fossae are contained within the inguinal (Hesselbach’s) triangle. The right medial fossa typically partially contains the cecum and/or ileum...
The medial umbilical folds are raised ridges of parietal peritoneum in the deep aspect of the anterior abdominal wall formed by the underlying medial umbilical ligaments. The paired folds run from pelvis to umbilicus. The medial umbilical ligaments are anatomical remnants of foetal umbilical art...
The median umbilical fold is a raised ridge of parietal peritoneum in the deep aspect of the anterior abdominal wall overlying the median umbilical ligament. It runs from the apex of the bladder to the umbilicus. The median umbilical ligament is the anatomical remnant of the foetal urachus. The ...
A mediastinal pseudocyst is the extension of pancreatic pseudocyst into the posterior mediastinum through oesophageal or aortic hiatus or rarely through the foramen of Morgagni. It is a rare complication of acute or chronic pancreatitis.
It can present with symptoms due t...
Medical devices in the abdomen and pelvis are important to be recognised, just like medical devices of the chest. Often we ignore these devices, considering them to be incidental and non-pathological, however it is essential to be aware of potential complications.
Mega oesophagus or diffuse oesophageal dilatation can be caused by a variety of conditions.
Some of the more common causes are given below 1-3:
malignant stricture, e.g. oesophageal canc...
Melioidosis is an infectious disease caused by Burkholderia pseudomallei (previously known as Pseudomonas pseudomallei) and is a multisystem disorder which may affect the lungs, brain, visceral organs, or musculoskeletal system.
Melioidosis is a disease of the monsoon season in th...
Ménétrier disease (MD) is a form of rare idiopathic hypertrophic gastropathy.
Rare disease with incidence < 1 per 200,000. Bimodal in distribution, children often < 10 years; adult forms 30-60 years, peak 55 years. Male preponderance both in juvenile and adult form 7.
In the gallbladder, the Mercedes-Benz sign describes a star-shaped pattern of gas-fissuring within gallstones initially described on an abdominal radiograph 2.
Fissures, usually fluid-filled, are present in close to 50% of gallstones. Less than half of these fissured gallstones contain some amo...
Mesenteric adenitis is a self-limiting inflammatory process that affects the mesenteric lymph nodes in the right lower quadrant, and is clinically often mistaken for acute appendicitis.
Mesenteric adenitis is most common in children and adolescents although it may occasionally aff...
Mesenteric cysts are a very rare cause of abdominal pain and have a wide range of underlying causes.
Mesenteric cysts are rare, with a reported incidence of 0.5-1 per 100,000 admissions 3.
Patients usually present with abdominal pain and/or mass, although...
Mesenteric desmoid tumours are a subtype of desmoid tumours
Desmoids are cytologically bland tumours that appear as infiltrative, well-demarcated tumours that are derived from musculo-aponeurotic structures throughout the body.
in the mesentery, the masses may occur...
A mesentery is a double layer of peritoneum that encloses the intestines and attaches them to the posterior abdominal wall. The term was originally only used to refer to the double layer of peritoneum that suspends the jejunum and ileum, but its meaning has been widened.
The mesoappendix is a fold of peritoneum around the vermiform appendix and one of the four mesenteries in the abdominal cavity.
It is attached to the lower end of the small bowel mesentery, close to the ileocaecal junction. It usually extends to the tip of the appendix and sometimes suspends th...
The mesorectal fascia is a layer of connective tissue enclosing the peri-rectal fat that surrounds the rectum. It is an important anatomical structure in rectal cancer staging.
location: envelopes the peri-rectal fat which surrounds the rectum within the pelvis
boundaries: extends fro...
Metaplasia is a general pathology term that refers to process when one cell type is replaced by another. It usually occurs in the context of a changed cellular environment to which the new cell type is better adapted 1. Examples include 2-5:
Barrett oesophagus: normal squamous epithelium replac...
MIBG scan is a scintigraphic study that uses metaiodobenzylguanidine labeled to iodine-123 or iodine-131. It is indicated in the investigation of phaeochromocytoma.
MIBG is positive in:
olfactory neuroblastoma 1
carcinoid tumour 4
The middle colic artery is a branch of the superior mesenteric artery (SMA). It passes in the layers of the transverse mesocolon to the transverse colon.
The middle colic artery divides into right and left branches. The right branch supplies the right portion of the transverse colon and anastom...
The middle rectal artery, also known as the middle haemorrhoidal artery, is a branch from the anterior division of the internal iliac artery supplying the rectum.
origin: anterior division of the internal iliac artery
supply: inferior rectum, seminal vesicles, prosta...
Midgut volvulus is a complication of malrotated bowel. It may result in proximal bowel obstruction with resultant ischaemia if prompt treatment is not instigated.
A midgut volvulus of malrotated bowel can potentially occur at any age but in approximately 75% of cases occur within ...
Misty mesentery is a term used to describe the CT appearance of mesenteric fat with increased attenuation. Just as with fat stranding elsewhere, a number of processes can lead to the appearance including infiltration by inflammatory cells, oedema, lymphatic accumulation, haemorrhage, tumour infi...
Mobile caecum is an anatomical variant and is often defined as a failure of the caecum, terminal ileum, and right colon, along with the mesentery, to fuse to the posterior parietal peritoneal wall. This results in increased mobility of the caecum.
It has been estimated to occur in...
The modified CT severity index is an extension of the original CT severity index (CTSI) was developed by Balthazar and colleagues in 1994 for distinguishing mild, moderate and severe forms of acute pancreatitis.
The original CT severity index has been followed internationally and has been very ...
Morgagni hernias are one of the congenital diaphragmatic hernias (CDH), and is characterised by herniation through the foramen of Morgagni. When compared to Bochdalek hernias, Morgagni hernias are:
more often right-sided (~90%)
rare (~2% of CDH)
at low risk of prolapse
The moulage sign is related to sprue, in particular coeliac disease. It occurs where there is a dilated jejunal loop with complete loss of jejunal folds 1. It is said to appear like a tube into which wax has been poured.
History and etymology
Moulage (French: casting/moulding) is the art of ap...
MR defaecography is a dynamic study for evaluation of the pelvic floor and pelvic organ prolapse.
There are four phases of evaluation:
Method of evaluation
Many variations in the techniques described below exist.
MR enteroclysis is a technique for evaluation of number of small bowel diseases (especially Crohn disease) using MRI.
A general technique is outlined below
placement of a nasoduodenal tube under fluoroscopic guidance
the small-bowel is distended with 1-3 L of methylcellulose (0.5%)...
MR enterography is a non-invasive technique for diagnosis of small bowel disorders.
The most common indication is to evaluate patients with Crohn disease (CD). Other less common indications would include coeliac disease, postoperative of adhesions, radiation enteritis, scleroderma,...
Mucinous adenocarcinomas of the appendix are on the malignant end of the spectrum of the mucinous neoplasms that affect the caecal appendix.
For the mucinous carcinomas involving the remainder of the colon, please refer to the article on mucinous carcinoma of the colon.
Mucinous carcinoma of the colon is a distinct form of colorectal cancer found in 10-15% of patients with colorectal cancer. It differs from the conventional adenocarcinoma in terms of clinical and histopathological characteristics.
For the caecal appendix, please refer to the article on mucinou...
Mucinous cystadenocarcinomas of the pancreas are a type of pancreatic mucinous tumour. It is considered the more malignant counterpart of a mucinous cystadenoma of the pancreas.
Like the more benign mucinous cystadenomas, these are found almost exclusively in females 4.
Mucinous cystadenomas (MCN) of the pancreas are a type of mucinous cystic neoplasm of the pancreas.
Previously believed to occur exclusively in middle age females 5, it has occasionally been described in males 6,7.
It is a large uni/multilocular cystic pancreatic neopl...
Mucinous cystic neoplasms of the pancreas are the most common cystic neoplasm of the pancreas and include:
mucinous cystadenoma of pancreas
mucinous cystadenocarcinoma of pancreas
intraductal papillary mucinous neoplasms (IPMN) of the pancreas: sometimes classified separately
Mucinous neoplasms of the appendix are epithelial tumours of the appendix that produce mucin. According to a panel of specialists consensus published in 2016, a new nomenclature and classification for the appendiceal mucinous neoplasms based on their histologic type and biologic behaviour has be...