What Is an Abdominal CT Scan?

The purpose of the abdominal CT examination is to understand whether there are infectious diseases in the abdominal organs, such as: inflammation, tuberculosis, abscess, etc .; whether there are occupants, such as benign, malignant tumors, metastatic tumors, etc .; whether there are deformities, stones, obstruction , Perforation, effusion, etc.

Name: Abdominal CT

category: Computed tomography computed tomography

Abdominal CT normal value

The normal CT manifestation CT image is a transverse image of the abdomen, which must be scanned according to the anatomy of each organ. (1) Liver CT can show liver outline, size, density, and internal structure. The density of normal liver is uniform, CT value is 40-70H, which is higher than that of spleen. At different levels, the size and shape of the liver leaves and segments displayed are different. If the hilum is layered, "H" -shaped low-density band shadows can be displayed. The right longitudinal fissure is the gallbladder fossa, the left longitudinal fissure is the hepatic sickle ligament, and the middle is the hepatic hilum, which contains the hepatic artery, portal vein, and hepatic duct. The left side of the left longitudinal fissure is the left lobe, the right side of the right longitudinal fissure is the right lobe, the square lobe is in front of the hepatic hilum between the two fissures, and the tail lobe is behind the hepatic hilum. (2) The gallbladder and biliary gallbladder are located in the gallbladder fossa with a transverse diameter of 4 cm. The capsule contains bile sweat, its density is 5-30H lower than that of adjacent liver tissue, and its shape is oval and round with clear boundaries. Normal intrahepatic and external bile ducts are not visualized and only show when dilated. Dilated bile ducts appear as dendritic low-density shadows extending from the hilum to the liver. Abdominal cross-section image Abdominal cross-section image (3) Pancreatic CT can show the outline, density, shape and size of the pancreas. The normal pancreas has a uniform density with a CT value of 40-50H, which is slightly lower than the surrounding organs. The pancreas looks like a lying silkworm and is divided into three parts: head, body and tail. Front and back diameter: 3cm at the head, 2.5cm at the body, and 2cm at the tail. (4) The spleen is crescent shaped. The density of the spleen is uniform, and the CT value is lower than that of the liver, which is similar to that of the pancreas. The size and length shall not exceed 5 rib units (a rib unit is equal to an intercostal or rib section). (5) Kidneys and adrenal kidneys are located on both sides of the spine. They can be oval or horseshoe-shaped at different levels. The horseshoe-shaped openings point inward and forward. Renal parenchymal density is uniform. The adrenal glands are "herringbone" or triangular in shape on the adrenal pole. (6) The large aorta abdominal aorta is located in the front left of the spine, and is round or quasi-circular. The inferior vena cava is located in the right front of the spine and is oblate. The portal vein is located in front of the caudate lobe.

Clinical significance of abdominal CT

Abnormal results:

First, liver disease

(1) Cirrhosis of the liver parenchyma causes different degrees of fat infiltration, fibrous tissue hyperplasia, and regeneration nodules. CT manifestations: Size: Liver enlargement caused by extensive fatty changes in the early stage, liver shrinkage in the late stage, improper proportion of left and right lobe size, widening of hilar and longitudinal fissure. Appearance: The nodules protrude and make the outer edge of the liver uneven, and also make the inner edge of the depression a bulge. Density: It decreases when fat changes. Limitations are reduced, and sometimes it is difficult to distinguish from primary or secondary cancer lesions. Splenomegaly is an important indirect sign of cirrhosis, but not all cirrhosis occurs. In portal hypertension, thick and tortuous blood vessels can be seen near the spleen hilum. Ascites sign: The distance between the liver and the abdominal wall increases, and a water-like density band shadow appears.

(2) Most fatty livers have extensive and even fatty infiltration. A few of them are limited. CT shows a decrease in liver density, which is lower than that of the spleen. In severe cases, the CT value is negative, so that the intrahepatic blood vessels show a high density density .

(3) Liver tumor CT has a high detection rate of liver tumors, and can determine the number, size and scope of tumors, but sometimes qualitative diagnosis is difficult. The CT of the liver cyst is a low-density spherical area with clear boundaries, and the CT value is similar to water. CT scan of hepatic spongiform hemangioma was a well-defined circular or oval low-density area. Dynamic enhancement scan showed nodular enhancement of the edge of the lesion, and gradually expanded to the center. After a period of time, the original density was restored. The length of time required for this process is directly proportional to the size of the lesion. This characteristic CT appearance is conducive to qualitative diagnosis. Primary hepatocellular carcinoma is a common liver malignant tumor in China. According to tumor size, it is divided into small liver cancer (less than 3cm), massive, multiple nodular and diffuse. CT scans show that most liver cancers are low density, but a few liver cancers are of equal density, and CT is not easy to detect. Low-density stoves are round, oval, lobed, or irregular. Lower density areas appeared due to necrosis and liquefaction in the tumor, and tumor nodules were seen in the middle and margins. In addition, the following indirect signs should be noted: the liver shape has limited bulges. Hepatic hilum, gallbladder, pancreas and stomach shift. 80% of liver cancers are associated with cirrhosis. Liver metastatic cancers often appear as multiple, circular, low-density areas within the liver that vary in size. Enhancement can be seen with tumor enhancement or ring signs. Differential diagnosis requires other clinical data.

(4) CT of liver abscess is a low-density circular or elliptical zone with clear boundaries. The CT value varies greatly depending on the contents of the abscess contents. If it contains gas, the gas-liquid surface can be seen, and the diagnosis can be determined. The contrast scan showed a circular sign on the edge of the abscess.

(5) Hepatic hydatid disease is a round or oval-shaped lesion with clear boundaries, thin walls, cystic wall often with calcification, and multiple ascites within the large sac.

Bile Duct Diseases

(1) Jaundice CT has high identification value for patients with jaundice. It can be determined whether it is obstructive jaundice, the plane of obstruction and the etiology of obstruction. Obstructive jaundice manifests as dilatation of the biliary system. Intrahepatic bile duct dilatation: a low-density dendritic shadow extending from the hilum to the liver appears in the liver without enhancement effect. Common hepatic duct and common bile duct dilatation: Oval or oval low-density shadows appear in the hilar or pancreatic head, which is the cross section of the expanded common bile duct, which is called ring sign. The gallbladder is enlarged. The determination of the obstruction plane is mainly based on the extent of biliary dilatation. Common hepatic duct obstruction: only intrahepatic bile duct dilatation, the gallbladder shrinks. Common upper bile duct obstruction: intrahepatic bile duct dilatation, ring signs in the hepatic hilum, no ring signs in the pancreatic head, and the gallbladder may increase. Bile duct obstruction: Intrahepatic bile duct dilatation, ring signs appear in the hilar and pancreatic head, ring signs are seen in several planes, no ring signs appear in the pancreatic head, and the gallbladder may be enlarged. Dilatation of the common bile duct can be seen on the uncinate process. The cause of obstruction must be determined by a comprehensive analysis of the site of obstruction, the presence or absence of lumps or stones, and other signs, combined with clinical data. The causes of obstruction are many, usually tumors, inflammation, and stones. The incidence is different in different planes, so the determination of the obstruction plane is helpful for the cause analysis.

(2) The gallstone CT value is proportional to the calcium content. Gallstones generally show high density in the gallbladder, varying in size and shape. Pure cholesterol stones, not developing. Gallstones are often associated with cholecystitis, and irregular thickening and calcification of the gallbladder wall is seen. Bile duct stones, in addition to showing the stones themselves, can also be seen in the bile duct obstructive expansion caused by stones.

(3) Gallbladder cancer Gallbladder cancer shows enlarged gallbladder, uneven thickening of the cyst wall, and uneven density. Enhanced scans show high-density block shadows and bile duct cancer. In addition to showing bile obstruction caused by cancerous tumors, it can also show cancer Masses of the liver itself or hilar.

Third, pancreatic diseases

The pancreas is a retroperitoneal organ, which is a difficult point for ordinary X-ray detection. CT can show the pancreas and its surrounding structure, so the diagnosis accuracy is high. (1) The direct signs of pancreatic cancer are a mass or local enlargement of the pancreas, which is more common in density, and a few are low density. Indirect signs are distal expansion of the pancreatic duct due to tumor invasion and compression. If the main pancreatic duct and common bile duct are dilated at the same time, a dual duct sign is displayed. If the pancreatic cancer spreads, it infiltrates the surrounding fat layer and blurs the outline. Lymphatic metastasis enlarges the lymph nodes around the pancreas and large blood vessels. Liver metastases and retroperitoneal metastases can cause ascites signs. (2) Pancreatitis Acute pancreatitis is characterized by pancreatic enlargement, deformation, and blurred edges. Chronic pancreatitis shows atrophy or enlargement of the pancreas, deformation, calcification, and pseudocysts.

Four, kidney disease

(1) Renal cysts mostly occur in the renal parenchyma. CT shows single or multiple round low-density areas with clear edges and CT values of 6-18H. (2) CT of renal cell carcinoma shows uneven density in the renal parenchyma, and calcium plaque is common. CT is easy to show when the cancer has metastasized to the aortic lymph nodes. (3) Most of the renal pelvis cancers are transitional cell carcinomas. The main CT manifestations are intrapelvic masses. About 50% of patients have hydronephrosis.

Five, adrenal tumors

Derived from the adrenal cortex and medulla. CT can detect tumors as small as 5mm ... When the adrenal glands are straight and convex, the tumor is highly suspected.

Six, other

Other organs in the abdomen, such as bladder, prostate, female genital tumors, and retroperitoneal lymph node metastases, can be diagnosed by CT. People to be examined: Patients with lesions and injuries of abdominal organs.

Cautions on abdominal CT

Unsuitable population: patients with severe heart and kidney failure and patients allergic to contrast media. Note before the test: (1) fast for 4 hours before the test, it is best to start fasting the night before. (2) CT scans of the lower abdomen were taken at 200-300 mL each at 8 and 10 pm the previous day and at 6 and 8 o'clock on the day of the test. Check the bladder after filling. (3) The method and time of taking the contrast agent will be explained to the patient in detail. (4) For patients who need enhanced scanning, family members are requested to sign the instructions for consent to receive the iodine contrast agent examination. If you have a history of drug allergies or a history of heart, liver and kidney dysfunction, please inform the medical staff to prevent accidents. (5) The detailed medical history and various test results must be notified to the CT doctor before the examination. If you keep the X-rays, magnetic resonance films, and previous CT films, you must give them to the CT doctor for reference. (6) Tell your doctor if you have a drug allergy or if you have allergic diseases such as asthma or urticaria. (7) The clothing to be removed from the inspection area includes underwear with metal materials and various items: headgear, hair clips, earrings, necklaces, jade pendants, coins, belts and keys. (8) For CT enhanced scans or children, unconscious, accompanied by a healthy person. (9) For CT enhanced scans, if an ionic contrast agent is used, an intravenous contrast agent iodine hypersensitivity test is required. After 20 minutes, there is no response before examination. (10) Do not take medicines containing heavy metals within one week, and do not perform gastrointestinal barium examination. Patients who have undergone a barium test should wait for the barium to be emptied; those who are anxious for a CT test should give a clean enema or oral laxative to make the barium complete before the CT test. Requirements during the inspection: (1) Follow the instructions of the technicians during the inspection, keep your body still, and cooperate with the inspection to calmly breathe, hold your breath, do not swallow, and do not blink. (2) Follow the doctor's order and drink the contrast medium regularly and quantitatively. (3) There is a walkie-talkie on the CT machine. If there is any discomfort or abnormal situation during the inspection, the doctor should be notified immediately.

Abdominal CT examination process

Patients usually need to drink a 2% iodine-containing contrast solution in water before the test. One of the objectives is to fill the entire intestinal cavity with contrast medium to reduce the artifacts caused by intestinal gas accumulation under X-rays. Artifacts affect the diagnostic effect; the second is: after the intestine is filled, it is easy to differentially diagnose the disease, so as to improve the accuracy of the diagnosis. Therefore, when you have finished drinking the contrast agent, you need a process. After the contrast agent has reached the intestinal cavity of the site you want to check, you can perform a CT examination. Suspected to be stones, such as: gallbladder stones, kidney stones, etc .; contrast pancreatitis, intestinal obstruction, and intestinal perforation usually do not need to drink contrast agents. This is to prevent the contrast agents from masking or aggravating the disease.

CT related diseases of the abdomen

Abdominal aortic aneurysm in the elderly, abdominal aortic constriction, omental torsion, acute appendicitis in AIDS patients, posterior wall perforated ulcers, chronic congestive splenomegaly in children, ileocecal syndrome in children, tuberculous mesenteric lymphadenitis, followed by Peritonitis, hepatic hydatid disease

Abdominal CT related symptoms

Four laziness, deep heat, deep depression, evil traps, yin, silent lying, Anhui abdomen, suffocation, abdomen pain without food, middle abdominal addiction, spider maggots, vomiting, reverse slipping, and vein exposure