The levator ani muscle, 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 fecal evacuation as well as maintaining continence.
The levator ani has three main ...
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 characterized 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 tumor 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 (DJ) flexure.
The ligament of Treitz comprises two parts, ...
The ligamentum teres or round ligament is the fibrous cord formed by the obliterated fetal umbilical vein that runs in the free edge of the falciform ligament from the umbilicus into the left lobe of the liver.
The ligamentum venosum is a fibrous remnant which travels superiorly from the porta hepatis 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...
The light bulb sign of an adrenal pheochromocytoma is an MRI feature of this tumor. It refers to marked hyperintensity on T2 weighted sequences, however, this finding is neither sensitive nor specific and pheochromocytomas are more often heterogeneous with intermediate or high T2 signal intensit...
The linea 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 um...
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 (hyperlipasemia) in numerous pancreatic, hepatobiliary and other diseases but is most commonly associated with acute pancreatitis.
Lipomas are benign tumors composed of mature adipocytes. They are the most common soft tissue tumor, seen in ~2% of the population.
Patients typically present in adulthood (5th-7th decades).
Typically lipomas are subcutaneous in location and present in adu...
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 ileocecal 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 tumors of fatty tissue and are the malignant counterpart to a benign lipoma. They are the second most common 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 is a rare, benign primary vascular tumor of the spleen.
Littoral cell angiomas may occur at any age and have no gender predilection.
Littoral cell angiomas have been diagnosed in association with various malignancies outside the s...
Littre hernia is a hernia containing a Meckel diverticulum, and is also known as a persistent omphalomesenteric duct hernia. It is most frequently encountered in the inguinal region.
blind-ending tubular structure arising from antimesenteric border of small bowel and ...
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 refers to abnormal lymph nodes that on CT appear to have lower attenuation than other soft tissues. This category can be split into two types:
cystic (necrotic) lymph nodes
metastatic carcinoma (or lymphoma)
infections (tuberculous or fungal)
Causes of calcifications in the lower abdomen and pelvis include:
seminal vesicle and ductus deferens calcification
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 hematochezia (bright red blood/clots or burgundy stools) or melena.
The incidence of lower gastrointe...
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 tumors of the appendix showing low-grade cytologic atypia, c.f. high-grade appendiceal mucinous neoplasms.
Considerable controversy still exists on mucinous ne...
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,...
Lymphoceles of the thoracic duct, also known as thoracic duct cysts, are lymph-filled collections/dilatations that can arise from any portion of the thoracic duct.
The clinical significance of a thoracic duct cyst lies in its misidentification as a pathological lesion at radiological assessment...
Lysosomal storage disorders (LSD) form a large group of clinical entities, more than forty now described, with the common etiological theme being the presence of dysfunctional lysosomal proteins, with the secondary accumulation of toxic metabolites inside the cellular lysosomes.
Macroamylasemia is the presence of serum amylase of a large molecular size, seen in both otherwise healthy individuals, and also in various diseases. Amylase seems to be able to self-polymerize and/or form complexes with other blood proteins, e.g. immunoglobulins.
Macrolipasemia is the presence of serum lipase of a large molecular size, seen occasionally in otherwise healthy individuals, but more commonly in various diseases. Lipase is able to self-polymerize and/or form complexes with other blood proteins e.g. immunoglobulins.
The term magenstrasse refers to a tubular portion of the stomach adjacent to the lesser curve of the stomach. It is a favored 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 common...
Magnetic resonance cholangiopancreatography (MRCP) is a non-invasive imaging technique to visualize the 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 patients to avoid sign...
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 esophageal neoplasms are much more common than benign esophageal neoplasms, especially if the patient is symptomatic.
esophageal carcinoma (90%)
esophageal squamous cell carcinoma (SCC)
esophageal spindle cell carcinoma
Malignant peritoneal mesothelioma is an uncommon primary tumor of the peritoneal lining. It shares epidemiological and pathological features with - but is less common than - its pleural counterpart, which is described in detail in the general article on mesothelioma. Other abdominal subtypes (al...
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 esophagus, 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 w...
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 vascularization, 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).
The differential diagnosis of a mass in the inguinal region includes:
hydrocele of the canal of Nuck
lymphadenopathy or necrotic lymph node
aneurysm or pseudoaneurysm of the femoral artery
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 the 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...
The McKeown procedure ("tri-incisional esophagectomy") is a type of esophagectomy, that is similar in concept to an Ivor Lewis procedure, but it tends to be used for esophageal lesions that are higher in the esophagus.
stomach mobilized, the esophagus
"gastric tube" may ...
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 bilateral raised ridges of parietal peritoneum in the deep aspect of the anterior abdominal wall formed by the underlying medial umbilical ligaments running from the pelvis to the umbilicus. The medial umbilical ligaments are anatomical remnants of the obliterated ...
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 representing the anatomical remnant of the foetal urachus. It is one of the 5 umbilical folds and should not be confused with the bilateral...
A mediastinal pseudocyst is the extension of pancreatic pseudocyst into the posterior mediastinum through esophageal 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 to...
Medical devices in the abdomen and pelvis are important to be recognized, 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.
Megaesophagus or diffuse esophageal dilatation can be caused by a variety of conditions.
Some of the more common causes are given below 1-3:
malignant stricture, e.g. esophageal cancer, ca...
Melioidosis is an infectious disease caused by the bacterium 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 monsoo...
Ménétrier disease (MD), also known as giant hypertrophic gastritis or hypoproteinemic hypertrophic gastropathy, 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 y...
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 (rare plural: adenitides) (less commonly called mesenteric lymphadenitis (rare plural: lymphadenitides)) is a self-limiting inflammatory process that affects the mesenteric lymph nodes in the right lower quadrant and is clinically often thought initially to be an acute append...
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 tumors are a subtype of desmoid tumors.
Desmoids are cytologically bland tumors that appear as infiltrative, well-demarcated tumors that are derived from musculo-aponeurotic structures throughout the body.
in the mesentery, the masses may occur spor...
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 ileocecal junction. It usually extends to the tip of the appendix and sometimes suspends the...
The mesorectal fascia is a layer of connective tissue enclosing the perirectal fat that surrounds the rectum. It is an important anatomical structure in rectal cancer staging.
location: envelopes the perirectal fat which surrounds the rectum within the pelvis
boundaries: extends from ...
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 esophagus: normal squamous epithelium replace...
MIBG scan is a scintigraphic study that uses metaiodobenzylguanidine labeled to iodine-123 or iodine-131. It is indicated in the investigation of pheochromocytoma.
MIBG is positive in:
olfactory neuroblastoma 1
carcinoid tumor 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 hemorrhoidal 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, prostat...
Midgut volvulus is a complication of malrotated bowel. It may result in proximal bowel obstruction with resultant ischemia 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 a...
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, edema, lymphatic accumulation, hemorrhage, tumor infiltr...
Mobile cecum is an anatomical variant and is often defined as a failure of the cecum, terminal ileum, and right colon, along with the mesentery, to fuse to the posterior parietal peritoneal wall. This results in increased mobility of the cecum.
It has been estimated to occur in 10...
Mobile cecum syndrome refers to a symptomatic mobile cecum, manifesting as chronic intermittent right lower quadrant pain and distension.
Uncommon diagnosis in that 10% of the population who have a mobile cecum, as it is usually asymptomatic.
Owing to a redundant mesoc...
The modified CT severity index is an extension of the original CT severity index (CTSI) which 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...
Morgagni hernias are one of the congenital diaphragmatic hernias (CDH), and is characterized 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 celiac 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/molding) is the art of appl...
MR defecography 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 an invasive technique for MRI evaluation of the small bowel mostly used in Crohn disease.
A general technique includes:
placement of a nasoduodenal tube under fluoroscopic guidance
small bowel distension with 1-3 L of methylcellulose (0.5%) and water solution or ...
MR enterography is a non-invasive technique for diagnosis of small bowel disorders.
MR enterography is most commonly used to evaluate patients with Crohn disease where it is used for assessment of the primary disease and any complications. Other indications include celiac disease, ...
Mucinous adenocarcinomas of the appendix are on the malignant end of the spectrum of the mucinous neoplasms that affect the cecal appendix.
For the mucinous carcinomas involving the remainder of the colon, please refer to the article on mucinous carcinoma of the colon.
The peak ...
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 cecal appendix, please refer to the article on mucinous...
Mucinous cystadenocarcinomas of the pancreas are a type of pancreatic mucinous tumor. 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 tumors of the appendix that produce mucin. They represent a spectrum of malignant potential, and are the most common cause of pseudomyxoma peritonei.
According to a panel of specialists consensus published in 2016 (Per...
Mucous fistulas are a surgically-formed connection between bypassed colon and the skin surface. It is a type of colostomy, but instead of letting ingested contents pass out of the body, a mucous fistula allows release of colonic secretions, mucus, and gas so that they do not build up over time...
Muir-Torre syndrome is a rare variant of hereditary nonpolyposis colorectal cancer (HNPCC), characterized by sebaceous neoplasms (e.g adenoma, epithelioma or carcinoma) and keratoacanthocytomas as well as at least one internal malignancy:
gastrointestinal malignancies (most common of internal ...
Multiple endocrine neoplasia type I (MEN1), also known as Wermer syndrome, is an autosomal dominant genetic disease that results in proliferative lesions in multiple endocrine organs, particularly the pituitary gland, islet cells of the pancreas and parathyroid glands.
There are other multiple...
Mushroom cap sign is one of the important signs of deep rectosigmoid endometriosis seen on T2 weighted MRI sequence. It indicates the submucosal involvement in the rectosigmoid colon.
The hypertrophic muscularis propria appears as heterogeneous low signal intensity surrounded by the high signal...
The mushroom sign (also called umbrella sign) is a radiological sign described in pyloric stenosis on barium examination.
This sign refers to the impression made by the hypertrophic pylorus on the duodenal cap.
double track sign
Mycosis fungoides (MF), also known as cutaneous T-cell lymphoma, is a type of malignant T-cell lymphoma that primarily involves the skin.
In the United States, it is more common in males and African Americans. In Europe, it accounts for ~6% of all non-Hodgkin lymphomas. It is rar...
Mycotic aneurysms are aneurysms arising from infection of the arterial wall, usually bacterial. It is a complication of the haematogenous spread of bacterial infection, classically from the heart.
The epidemiology of mycotic aneurysms mirrors that of identifiable risk factors:
Myochosis coli is an uncommonly used term to denote the shortening and thickening of the colon seen in diverticulosis.
This is due to shortening of the taeniae coli and thickening of the circular muscular layer 1.
History and etymology
Myochosis coli is from the Ancient Greek for "heaped-up ...
Assessment of nasogastric (NG) tube positioning is a key competency of all doctors as unidentified malpositioning may have dire consequences, including death.
Evaluation of NGT
The ideal position should be in the subdiaphragmatic position in the stomach - identified on a plai...