Exercise: Extraluminal Gas Pattern

EXERCISE 8-6. EXTRALUMINAL GAS PATTERN

8-21. What is the most likely diagnosis in Case 8-21 (Figure8-46)?

A.   Colonic diverticulitis

B.   Mechanical obstruction of the colon

C.   Pneumatosis cystoides intestinalis

D.   Pneumoperitoneum

8-22. What is the most likely diagnosis in Case 8-22 (Figure8-47)?

A.   Abscess

B.   Functional ileus

C.   Gallstone ileus with gas in the biliary tree

D.   Hepatic portal vein gas

8-23. What is the most likely diagnosis in Case 8-23 (Figure8-48)?

A.         Gallstone ileus with gas in the biliary tree

B.         Hepatic portal venous gas

C.         Pneumoperitoneum

D.         Right subdiaphragmatic abscess.

8-24. What is the most likely diagnosis in Case 8-24 (Figure8-49)?

A.         Gallstone ileus with gas in the biliary tree

B.         Hepatic portal venous gas

C.         Pneumoperitoneum

D.         Subdiaphragmatic abscess

Radiologic Findings

8-21. This case shows linear air streaks along the descend-ing and sigmoid colon in a patient with mild ab-dominal pain. These streaks indicate pneumatosis cystoides intestinalis (C is the correct answer to Question 8-21).

8-22. This case shows a distended proximal jejunum and a few air bubbles in the right upper quadrant, indicat-ing gallstone ileus with mechanical obstruction and air in the biliary tree (Figure 8-50 A). An upper gas-trointestinal study demonstrates a distended proximal small bowel, a fistula (Figure 8-50B) between the bil-iary tree and the duodenum, and three gallstones in the small bowel (Figure 8-50 C). CT shows air in the biliary tree (Figure 8-50 D) (C is the correct answer to Question 8-22).

8-23. In this case, multiple air bubbles in the right upper quadrant in a patient with fever are consistent withsubdiaphragmatic abscess (Figure 8-51). Bilateral linear rib calcifications and right hip replacement are also seen (D is the correct answer to Question 8-23).

8-24. This case shows a fine arborizing linear gas pattern in the right upper quadrant extends to the periphery of the liver, indicating portal venous gas (B is correct answer to Question 8-24).

Discussion

Pneumatosis cystoides intestinalis appears as linear streaks of gas or intramural cystic collections of gas in the small bowel or colon. The cysts range in size from 0.5 to 3 cm and may extend into the adjacent mesentery. Pneumatosis intestinalis is an incidental finding in most patients, usually with a self-limited benign course; simple bowel obstruction, volvulus, and air from the mediastinum or retroperitoneum are commonly associated. Pneumatosis intestinalis may be caused by ischemic and necrotizing enterocolitis in patients with leukemia or non-Hodgkin lymphoma and in those who have had bone marrow transplantation.

Gallstone ileus, the mechanical obstruction of the small bowel by an impacted gallstone, is commonly seen in elderly women. Clinical presentation in gallstone ileus is nonspecific, and the mortality rate is high (15%). A gallstone enters the intestinal lumen via a cholecystoenteric fistula. Major radi-ographic signs include small-bowel obstruction, air in the biliary tree, and an ectopic gallstone seen on plain abdominal film, upper gastrointestinal series, or CT study.

Abscess in the subphrenic and subhepatic spaces is a se-rious problem, with a mortality rate of 30%. Subphrenic abscess may arise spontaneously or as a complication of ab-dominal surgery, pancreatitis, diverticulitis, or appendicitis. A cluster of gas may be seen on plain film in 70% of abscesses. Left-sided abscess is difficult to discern because gas in the splenic flexure, stomach, or jejunum may mimic gas within the abscess. Other radiographic findings include elevation of the adjacent hemidiaphragm, pleural effusion, and basilar at-electasis. CT is more accurate in assessing hepatic and extra-hepatic abscess (Figure 8-52).

In the right upper quadrant, when multiple tubular lu-cencies are seen reaching the lateral hepatic margins, portal venous gas is a likely consideration (Figure 8-53). Biliary tree gas is located in the central hepatic zone near the porta he-patis. Benign portal venous gas has been noted in sigmoid diverticulosis, nonobstructed splenic flexure carcinoma, ul-cerative colitis, and bronchopneumonia. Mesenteric vascular insufficiency and necrotizing intestinal infection are common causes of hepatic portal venous gas. In children, necrotizing enterocolitis produces intramural gas within mesenteric veins to the liver; the mortality rate in patients with the sign of hepatic portal venous gas is higher than in those without portal venous gas.