Gastrointestinal

Gastrointest Radiol 9:107-113 (1984)

Radiology 9 Springer-Verlag 1984

The Triangle Sign: A CT Sign of Intraperitoneal Fluid Robert J. Rust 1, Kenyon K. Kopecky, and Robert W. Holden Department of Radiology, Wishard Memorial Hospital, Indiana University Medical Center, Indianapolis, Indiana, USA

Abstract. Ninety-four abdominal CT examinations of 91 patients with intraperitoneal fluid were reviewed, and in 25 scans (27%) triangular fluid collections were found within the leaves of the mesentery or adjacent to bowel. In a control group of 30 patients without CT evidence of intraperitoneal fluid, no triangular densities were identified. Triangular fluid collections were visualized in a higher percentage of patients when the quantity of intraperitoneal fluid was moderate to large, IV contrast was given, good bowel opacification was obtained, the amount of mesenteric fat was moderate to large, and the abdominal CT examination included cuts through the pelvis. A triangular fluid collection was reproduced in a cadaver by intraperitoheal infusion of saline. Percutaneous needle aspiration confirmed that the saline collection was responsible for the CT findings. The CT appearance of this new triangle sign is demonstrated. Key words: Ascites - Hemoperitoneum - Computed tomography, intraperitoneal fluid.

Many of the varied CT appearances of ascites have been described [1, 2]. The triangle sign of pneumoperitoneum, a s seen on plain films, representing gas trapped between bowel loops, has also been described [3]. However, CT demonstration of the triangle sign of fluid trapped between bowel loops, similar to the triangle sign of air between bowel loops representing pneumoperitoneum [3], has not been described for ascites. This study was underPresent address: Consulting Radiologists, Ltd., Abbott Northwestern Hospital, Minneapolis, MN Address reprint requests to: Robert W. Holden, M.D., Department of Radiology, Wishard Memorial Hospital, Indiana University Medical Center, 1001 West 10th Street, Indianapolis, IN 46202, USA

taken to characterize this new sign, to document that the sign is due to intraperitoneal fluid accumulation, to determine its incidence, and to ascertain the conditions in which it is seen. Materials and Methods Ninety-four abdominal CT examinations in 91 patients performed between January 1982 and January 1983 in which the Table 1. Clinical findings in 94 patients

%*

No triangular fluid collections seen (A)

One or more triangular fluid collections (B)

(n)

(n)

Amount of fluid in upper abdomen Small Moderate-large

30 39

6 19

20 49

Amount of fluid in pelvis Not scanned Small Moderate-large

21 22 26

1 2 22

5 5 85

Intravenous contrast No Yes

15 54

2 23

13 43

Oral contrast No Yes

12 57

4 21

25 37

Rectal contrast No Yes

51 18

14 11

27 61

Bowel opacification Poor Fair-good

31 38

9 16

29 42

Amount of mesenteric fat Small Moderate-large

38 31

5 20

13 65

* Percentage of patients with one or more triangular fluid collections = B/(A + B) x 100

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R.J. Rust et al. : Triangle Sign in CT of Intraperitoneal Fluid

Fig. 1. Scan of a 57-year-old man with hemoperitoneum demonstrates a triangular collection of blood (arrows) Fig. 2. A 37-year-old m a n with hemoperitoneum showed a similar accumulation of blood between mesenteric leaves (arrows) on CT scan

diagnosis of intraperitoneal fluid was made from the CT study were reviewed. The CT diagnosis of intraperitoneal fluid was made in each case in accordance with the descriptions of Jolles and Coulam [1]. Thirty consecutive CT scans in 30 patients without CT evidence of intraperitoneal fluid, in whom both the abdomen and pelvis were scanned, were reviewed as a control group. Scans were performed on a Picker Synerview 600 or a Philips Tomoscan 310 with scan times of 3.3 and 4.8 s, respectively. All studies were reviewed by 2 of us (RR and KK) and interobserver differences were resolved by joint review. In each case note was made of clinical diagnoses; quantity of intraperitoneal fluid in the upper and lower abdomen; presence or absence of IV, oral, and rectal contrast media; quality

of bowel opacification; quantity of mesenteric fat; and number of triangular fluid collections seen adjacent to the mesentery or bowel. Triangular collections in the paracolic gutters were not included since fluid accumulations in these regions have been previously described [1]. Quantitation of the above factors was necessarily subjective. A fresh cadaver the body of a person who had died from a head injury and had no abdominal disease - was obtained. The abdomen and pelvis were scanned without contrast using contiguous sections 1 cm thick. A catheter was then placed intraperitoneally under direct vision via a cutdown in the midline superior to the umbilicus, 2000 ml of normal saline was infused, and a repeat scan performed.

R.J. Rust et al. : Triangle Sign in CT of Intraperitoneal Fluid

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Fig. 3. Scan of a 56-year-old woman with disseminated adenocarcinoma and malignant ascites (arrows) Fig. 4. Scan of a 76-year-old man with cecal carcinoma metastatic to the liver. Triangular collection of ascites is visible (arrow)

Results

Triangular fluid collections were observed in 25 of 94 (27%) scans showing intraperitoneal fluid. If those in which the pelvis was not scanned were excluded the sign was seen in 24 of 72 (33%) (Table 1). The clinical diagnoses were varied and no correlation between the patients' underlying diseases and the appearances of triangles was observed. The underlying diseases included cirrhosis, trauma, infection, inflammation, and neoplasm.

Those patients with a moderate or large amount of intraperitoneal fluid, those receiving intravenous contrast, those with good bowel opacification, those whose scans included the pelvis, and those with a moderate or large amount of mesenteric fat had a higher incidence of visualized triangular fluid collections. Examples of hemoperitoneum in 2 patients with ruptured spleens are shown in Figures 1 and 2. The triangular fluid collections between the mesenteric leaves and bowel loops are easily seen be-

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R.J. Rust et al. : Triangle Sign in CT of Intraperitoneal Fluid

Fig. 5. Findings in a 67-year-old woman with pancreatitis and ascites (arrows) Fig. 6. Scan of a 55-year-old patient with ovarian carcinoma and malignant ascites (arrows)

cause of the high density of fresh blood. Intraperitoneal fluid was seen on multiple cuts around the liver and spleen, in Morison's pouch, and in the pelvis. In Figures 3 and 4 triangular fluid collections are seen completely surrounded by mesenteric fat. Triangular accumulations of ascites bordered on 2 sides by mesenteric fat and on I side by bowel are shown in Figures 5 and 6. A fluid collection between the anterior abdominal wall and contrast-filled colon (Fig. 7) was also demonstrated. Figure 8 illustrates fluid accumulation be-

tween the mesentery and posterior peritoneum adjacent to the psoas muscle. A triangular fluid collection surrounded by fluid filled bowel is seen in Figure 9. This patient had mechanical small-bowel obstruction with multiple fluid-filled bowel loops in addition to ascites. This is the only case in which the location of the triangular fluid collection is uncertain: one cannot discern from the scan alone whether the fluid is between unopacified bowel loops or within bowel itself. In the 30 control patients without CT evidence

R.J. Rust et al. : Triangle Sign in CT of Intraperitoneal Fluid

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Fig. 7. A 58-year-old woman showed ovarian sarcoma and ascites (arrows) on CT scan

Fig. 8. Findings in a 40-year-old man with gastric adenocarcinoma, peritoneal metastases, and ascites (arrow) Fig. 9. A 58-year-old woman with ovarian carcinoma, peritoneal metastases, and small bowel obstruction. Triangular fluid accumulation is visible (arrows) on CT scan

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R.J. Rust et al. : Triangle Sign in CT of Intraperitoneal Fluid

Fig. 10. Cadaver. A C T section before intraperitoneal infusion of saline. B CT section at same level after infusion of saline. Triangular fluid collection developed between mesentery and air-filled bowel (arrows). C Percutaneous needle tip (straight arrow) within fluid collection. Needle shaft is out of plane of section

R.J. Rust et al. : Triangle Sign in CT of Intraperitoneal Fluid

of intraperitoneal fluid, no triangular densities within the abdomen or pelvis were seen. There were no significant differences between the control group and the patients with intraperitoneal fluid regarding any of the parameters: bowel opacification, presence or absence of IV contrast, quantity of mesenteric fat, or clinical diagnoses. A cadaver was scanned before intraperitoneal instillation of saline (Fig. 10A). Figure 10B demonstrates the appearance of the triangular fluid collection after saline infusion. The collection was then percutaneously aspirated with an 18-gauge needle (Fig. 10C), and 3 cc of clear saline was removed. The presence of clear saline only confirmed that the collection was not a bowel loop filled with succus entericus.

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fluid collections in the subhepatic space, Morison's pouch, around the liver and spleen, in the paracolic gutters and the pelvic cul-de-sacs, and in a serpentine configuration radiating from the root of the mesentery have been described [1, 2]. Our study indicates an additional finding: fluid frequently accumulates in triangular configurations within the leaves of the mesentery or adjacent to bowel loops. This does not appear to be an early finding in ascites since most patients with this finding had moderate or massive amounts of fluid. It is important, however, because it is a frequent finding that needs to be explained and understood by the radiologist. References

Discussion

Intraperitoneal fluid is a common finding in many disease states: trauma, cirrhosis, portal vein thrombosis, neoplasm, inflammatory disease, nephrosis, and metabolic and cardiac disorders. It may be an early or late manifestation of the underlying disease [4]. Computed tomography is a sensitive and specific method for the detection of intraperitoneal fluid, and the CT characteristcs are welldescribed. The CT appearances of intraperitoneal

1. Jolles H, Coulam CM : CT of ascites : differential diagnosis. A JR 135:315 322, 1980 2. Roub LW, Drayer BP, Orr DP, Oh KS: Computed tomographic positive contrast peritoneography. Radiology 131 : 69%704, 1979 3. Miller RE: The radiological evaluation of intraperitoneal gas (pneumoperitoneurn). CRC Crit Rev Radiol Sc : 61-85, 1973 4. Glickman RM, Isselbacher K J: Abdominal swelling and ascites. In: Harrison's Principles of Internal Medicine, 9th ed. New York: McGraw-Hill, 1980, pp 210-213

Received." September 22, 1983; accepted: November 8, 1983