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(Radiology. 2001;219:229-235.)
© RSNA, 2001

Emergency Radiology

US of Blunt Abdominal Trauma: Importance of Free Pelvic Fluid in Women of Reproductive Age1

Claude B. Sirlin, MD, Giovanna Casola, MD, Michèle A. Brown, MD, Nirav Patel, MD, Eli J. Bendavid, MD, Reena Deutsch, PhD and David B. Hoyt, MD

1 From the Departments of Radiology (C.B.S., G.C., M.A.B., E.J.B.), Surgery (N.P., D.B.H.), and Family and Preventive Medicine (R.D.), UCSD Medical Center, 200 W Arbor Dr, San Diego, CA 92103-8756. From the 1998 RSNA scientific assembly. Received April 14, 2000; revision requested June 6; revision received June 30; accepted August 8. R.D. supported in part by National Institutes of Health grant M01 RR00827. Address correspondence to C.B.S. (e-mail: csirlin@ucsd.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
PURPOSE: To assess the importance of free fluid and to determine the accuracy of screening ultrasonography (US) in female patients of reproductive age with trauma.

MATERIALS AND METHODS: US was performed in 1,047 patients, aged 10–60 years, to evaluate blunt trauma. Patients were retrospectively assigned to groups on the basis of presence and location of intraperitoneal free fluid. Injury and surgical injury rates were assessed by comparing US results with computed tomographic, repeat US, cystographic, peritoneal lavage, surgical, and/or autopsy findings in 144 patients and with final clinical outcome in 903. US scans were positive if fluid was outside the cul-de-sac or if suspicious parenchymal abnormalities were present.

RESULTS: In 939 patients, no fluid was seen: Eight had injuries; three were surgical. In 56, anechoic fluid was isolated to the cul-de-sac: Two had injuries; one was surgical. In 26, fluid was isolated to the upper abdomen: Fifteen had injuries; five were surgical. In 22, fluid involved the pelvis and abdomen: Nineteen had injuries; 14 were surgical. In four, questionable fluid was isolated to the supravesical space. Patients with fluid in the cul-de-sac had similar injury and surgical injury rates as those with no fluid but had lower rates than those of patients with fluid elsewhere (P < .02 to P < .001). US screening had 89% sensitivity, 98% specificity, 97% accuracy, a 61% positive predictive value, and a 99% negative predictive value.

CONCLUSION: In female patients of reproductive age with trauma, free fluid isolated to the cul-de-sac is likely physiologic; clinical follow-up should suffice. Patients with fluid elsewhere usually have clinically important injury and require further evaluation.

Index terms: Abdomen, injuries, 70.41 • Abdomen, US, 70.1298 • Kidney, injuries, 81.41 • Liver, injuries, 761.41 • Pelvic organs, US, 761.1298, 775.1298 • Peritoneum, fluid, 791.41 • Spleen, injuries, 775.41


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
During the past several years, ultrasonography (US) has become an important modality in many centers in the screening of blunt abdominal trauma. US is relatively inexpensive, can be performed rapidly and with a mobile unit in the trauma resuscitation room, and is noninvasive. Sensitivities of 63%–99% and accuracies of 85%–99% have been reported (1–14), with most investigators emphasizing the detection of free fluid in the peritoneal cavity as the most important factor in screening for abdominal injury.

Consequently, abdominal fluid detected at US is considered abnormal and should lead to additional assessment and/or intervention; however, the interpretation of free fluid in female patients of reproductive age is not straightforward because fluid in the cul-de-sac (CDS) may be physiologic (15–24). We hypothesized that in female patients of reproductive age with trauma, anechoic fluid within the CDS is physiologic rather than traumatic and requires no further evaluation in the absence of other clinical or imaging findings. The purpose of this study was to assess the importance of free fluid and to determine the accuracy of screening US in female patients of reproductive age with trauma.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Patients
All 1,048 female patients, aged 10–60 years (mean age, 33 years), who were screened with US for blunt abdominal trauma and admitted to the trauma surgery service at a level I center from April 1994 through December 1998 were considered for the study. At our institution, all patients who present with blunt trauma during the hours of US availability are screened with sonography (hours of availability fluctuated during the study period for personnel reasons, but they generally were 7:00 AM to 11:30 PM) at the discretion of the trauma service; formal inclusion and exclusion criteria are not used. Patients who present at other times are screened with computed tomography (CT). Because we did not prospectively document obstetric and menstrual histories in all patients, the age range of 10–60 years was chosen to represent the reproductive years. One patient had an uninterpretable US scan because of subcutaneous emphysema and was excluded. The remaining 1,047 patients formed the basis of this study. Mechanisms of injury are summarized in Table 1. Traffic accidents accounted for 78% of presentations. Eighty-nine patients (8.5%) were pregnant (age range, 14–43 years).


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  		TABLE 1. Mechanisms of Blunt Injury
 
This study received full approval from the institutional review board. Informed consent was not routinely obtained, as abdominal US has been approved for waived consent by the investigational review board in the setting of trauma.

Patient data were entered prospectively into a computerized database, and patients were followed up clinically by the surgical staff (including D.B.H., N.P.) during their hospital stay and at follow-up visits in the clinic. Additional examination of patients, including CT, repeat US, cystography, diagnostic peritoneal lavage (DPL), and laparotomy, was pursued on an individual basis, usually because of a positive US finding or because clinical suspicion of injury was high despite a negative US finding. Patients with positive US findings and hemodynamic instability underwent laparotomy without preoperative confirmation of injury. To monitor potential delayed clinical complications after discharge, the trauma service participated in the county quality assurance program, which meets monthly to review trauma admissions and complications for the entire county.

US Examinations
Scans were obtained during resuscitation by experienced sonographers (1–20 years of experience) with US equipment (ATL HDI 3000, Advanced Technologies Laboratories, Bothell, Wash; 128-XP, Acuson, Mountain View, Calif) in the presence of a staff or resident radiologist (including G.C.). Usually, a 3.5-MHz sector transducer was used. If needed for more optimal imaging, 2.25- or 5.0-MHz sector and 5.0-MHz curved-array transducers were used, but we did not document the number of studies in which this was done. Hard-copy images were obtained with the Image Link system (Eastman Kodak, Rochester, NY) and were interpreted prospectively by the resident and attending radiologist on call by consensus.

Each examination was performed with the patient’s bladder full; if needed, the bladder was distended with 200–300 mL of sterile normal saline by using a Foley catheter. The number of times in which this was necessary was not recorded, as bladder catheterization is routinely performed by the trauma service. Seven regions in the abdomen, including the pelvis, both paracolic gutters, both upper quadrants, and both renal fossae, were examined for fluid. The presence of free fluid was prospectively assessed. In addition, solid organs (liver, spleen, and kidneys) were evaluated for parenchymal abnormalities suggestive of injury. Because the location of fluid was not recorded prospectively, sonograms that demonstrated free fluid were retrospectively reviewed by an experienced radiologist (G.C.) who was blinded to the final outcome and who recorded the location of all fluid pockets. Sonograms that depicted no free fluid were not reviewed but were included in the analysis.

Patients were then assigned to five groups on the basis of the presence and location of intraperitoneal fluid, as follows: (a) no intraperitoneal fluid, (b) fluid isolated to the CDS (rectouterine recess) and/or contiguous pelvic (ovarian, vesicouterine, and lateral paravesical) recesses, (c) fluid immediately superior to the urinary bladder in the supravesical space (SVS), (d) fluid isolated to the abdomen (the right and left upper quadrants and the right and left paracolic gutters), and (e) fluid in both the pelvis and abdomen.

Fluid pockets in the pelvis were evaluated for the presence of internal echoes and were measured by estimating their anteroposterior depth in millimeters from the photographed images. Fluid pockets in the abdomen were not measured. The presence of extraperitoneal fluid, principally in the retroperitoneum or retropubic space, and parenchymal abnormalities suggestive of injury were noted and assessed separately.

After the location and appearance of all fluid pockets were documented, sonograms were retrospectively interpreted as negative if they depicted no fluid or if they depicted simple fluid in the CDS, as this was hypothesized to be physiologic rather than traumatic in this patient population. Sonograms were considered positive if pelvic fluid was complex, if there was fluid elsewhere in the abdomen, or if suspicious parenchymal abnormalities were present.

Data and Statistical Analysis
US results were compared with clinical outcome and CT, repeat US, cystographic, DPL, surgical, and/or autopsy findings, as summarized in Table 2. (All CT examinations were performed after screening US. The interval ranged from 8 minutes to 22 days, with a median of 65 minutes. Seventy-six [75%] of 101 CT examinations were performed within 3 hours of US.) The injury rate (percentage of patients with actual injuries) and laparotomy rate (percentage of patients who underwent therapeutic laparotomy) for the five groups were compared by using a {chi}2 exact test. A global exact test was initially performed to confirm that statistically significant differences existed in the rates of injury and laparotomy among the patient groups at a 5% significance level. Pairwise comparisons were then made to identify where these differences were first by using group 1 (no intraperitoneal fluid) and then group 2 (CDS fluid) as the reference. No adjustments for multiple comparisons were made.


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  		TABLE 2. Additional Examinations Performed in 144 Patients
 
The mean depth (and SD) of physiologic pelvic collections (pelvic collections in uninjured group 2 patients) and of traumatic pelvic collections (pelvic collections in injured group 5 patients) were statistically compared (by using the Wilcoxon rank sum nonparametric test).

The sensitivity, specificity, accuracy, positive predictive value, negative predictive value, and likelihood ratios for positive and negative findings at sonography for the identification of patients with clinically important injuries were calculated. The positive predictive value of sonography for the detection of fluid, as opposed to injury, was also calculated by evaluating the subset of patients who underwent CT, repeat US, and/or surgery and/or those who died and were examined at autopsy after sonographic screening revealed free fluid anywhere within the abdomen or pelvis. (Patients who underwent only clinical, DPL, or cystographic follow-up were excluded from the fluid detection analysis.) A 95% CI estimate for the rates was determined by using normal distribution methods or simulation (1,000 repetitions) when N was insufficiently large to satisfy normal distribution assumptions.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
Of 1,047 women screened for blunt abdominal trauma, 44 (4.2%) had documented intraabdominal injuries. Because some patients had multiple injuries, there were a total of 22 extraperitoneal (eight adrenal gland, five kidney, one pancreas, one duodenum, three retroperitoneal hemorrhage, two extraperitoneal bladder, two uterus) and 54 intraperitoneal (13 liver, 13 spleen, 12 bowel, 14 mesentery, and two intraperitoneal bladder) injuries. US depicted no intraperitoneal fluid in 939 of 1,047 patients. In the other 108, intraperitoneal fluid was observed: 56 in the CDS and contiguous recesses, four in the SVS, 26 in the upper abdomen, and 22 in the abdomen and pelvis.

No Intraperitoneal Fluid
In the 939 patients (mean age, 33 years; age range, 10–60 years) with no intraperitoneal fluid, further evaluation revealed a total of 14 injuries (one liver, two spleen, two mesentery, one bowel, one extraperitoneal bladder, one adrenal gland, three kidney, two uterus, one retroperitoneal hematoma) in eight patients, as confirmed with five CT scans, two cystograms, and two obstetric US scans. Three of the eight patients required laparotomy: two patients with placental abruptions who underwent emergency cesarean delivery, and one patient with mesenteric and bowel lacerations. Although no intraperitoneal fluid was identified in the eight patients, the sonogram was prospectively interpreted as positive for injury in four, including one of the three who required laparotomy because of focal extraperitoneal abnormalities. No injuries were discovered because of intraperitoneal parenchymal abnormalities.

The other 931 patients in this group had no abdominal injuries. Sixty underwent one or more confirmatory tests, including 32 CT examinations, 13 repeat US examinations, 11 cystographic examinations, three DPLs, and two exploratory laparoscopies; three autopsies were performed in those who died of nonabdominal causes. Eight hundred seventy-one underwent no additional tests but had a benign clinical course during hospitalization and at clinical follow-up, and no injuries were discovered at monthly audits of the county trauma system.

Fluid Isolated to the CDS and Contiguous Recesses
In 56 patients (mean age, 26 years; age range, 15–54 years), anechoic free fluid was identified within the CDS and/or contiguous pelvic recesses. Of the 56 patients, 31 had fluid in only the rectouterine recess. The rest had fluid in adjacent pelvic recesses (Fig 1). Fluid did not extend over the bladder dome into the SVS in any patient.



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  		Figure 1a. (a) Transverse transabdominal US image in a 30-year-old woman reveals a small pocket of anechoic fluid (straight arrow) in the rectouterine recess extending into the right ovarian fossa (curved arrow), as confirmed with (b) transverse contrast material-enhanced CT scan.

 


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  		Figure 1b. (a) Transverse transabdominal US image in a 30-year-old woman reveals a small pocket of anechoic fluid (straight arrow) in the rectouterine recess extending into the right ovarian fossa (curved arrow), as confirmed with (b) transverse contrast material-enhanced CT scan.

 
In 54 (96%) of 56 patients, there was no evidence of abdominal injury. Twenty-five underwent one or more confirmatory tests, including three repeat US examinations, 20 CT examinations, and three DPLs; two who died were examined at autopsy. In two patients, endovaginal US was necessary to document anechoic fluid in the CDS after screening US findings showed questionable echoes within the pelvic fluid (Fig 2). Twenty-nine patients underwent no additional tests but had a benign clinical course. Among the 54 uninjured patients, fluid pockets (representing physiologic collections) ranged from 3 to 35 mm in anteroposterior dimension, with a mean of 13 mm ± 7 (SD). Forty-one (76%) of 54 pockets were between 5 and 15 mm; two (4%) were at least 3 cm.



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  		Figure 2a. (a) Longitudinal transabdominal US image in a 37-year-old woman depicts a small fluid collection with questionable echoes and dependent debris, which possibly represents pelvic hemoperitoneum, in the CDS (arrow). b = bladder, u = uterus. (b) Sagittal transvaginal scan shows that the fluid (arrow) is anechoic, which suggests a physiologic cause. bo = bowel, u = uterus.

 


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  		Figure 2b. (a) Longitudinal transabdominal US image in a 37-year-old woman depicts a small fluid collection with questionable echoes and dependent debris, which possibly represents pelvic hemoperitoneum, in the CDS (arrow). b = bladder, u = uterus. (b) Sagittal transvaginal scan shows that the fluid (arrow) is anechoic, which suggests a physiologic cause. bo = bowel, u = uterus.

 
Two (4%) of 56 patients had a documented injury. One was a 20-year-old woman with bilateral ovarian cysts and 1–2-cm fluid pockets in the rectouterine recess and ovarian fossae (Fig 3a). Although the fluid met our criteria for being physiologic, clinical suspicion of injury was high due to pelvic fractures and gross hematuria. CT findings confirmed fluid in the CDS and also showed a small fluid collection in the right iliac fossa (Fig 3b) just inferior to the portion of the right lower quadrant that had been screened with US. CT findings led to conventional cystography, which demonstrated focal extravasation from the bladder dome. At laparotomy, the bladder laceration measured 1 cm, and the fluid in the CDS was clear. Although the fluid pocket in the iliac fossa was traumatic, the fluid in the CDS likely was physiologic and incidental.



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  		Figure 3a. (a) Longitudinal transabdominal US image of the pelvis in a 20-year-old woman shows a small collection (arrow) in the CDS. b = bladder, u = uterus. (b) Transverse contrast-enhanced CT scan reveals a focal fluid collection in the right iliac fossa (arrow), which was not depicted at screening US. Low-attenuating fluid identical to the collection seen at US was confirmed on a more inferior image (not shown). A 1-cm bladder dome laceration was found at cystography and confirmed at laparotomy.

 


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  		Figure 3b. (a) Longitudinal transabdominal US image of the pelvis in a 20-year-old woman shows a small collection (arrow) in the CDS. b = bladder, u = uterus. (b) Transverse contrast-enhanced CT scan reveals a focal fluid collection in the right iliac fossa (arrow), which was not depicted at screening US. Low-attenuating fluid identical to the collection seen at US was confirmed on a more inferior image (not shown). A 1-cm bladder dome laceration was found at cystography and confirmed at laparotomy.

 
The other patient with a documented injury in this group was a 21-year-old woman with a 3.5-cm hyperechoic adrenal mass detected at screening US in addition to 5 mm of fluid in the CDS. Follow-up CT findings demonstrated low-density fluid in the CDS and confirmed a focal hematoma in the adrenal gland. She did well clinically without surgical intervention. The fluid in the CDS was likely physiologic and unrelated to the adrenal injury.

Fluid Isolated to the SVS
Four patients (mean age, 41 years; age range, 18–58 years) had questionable hypoechoic collections in the SVS, all were evaluated with follow-up CT. In three patients, the sonographic abnormality proved to be a fluid-filled bowel. In the other patient, an anteverted uterus was mistaken for a focal fluid collection. None of the patients had abdominal injuries.

Fluid Isolated to the Upper Abdomen
Twenty-six patients (mean age, 35 years; age range, 14–56 years) had intraperitoneal fluid exclusively in the abdomen: 23 with fluid in a single upper quadrant, two with fluid in both upper quadrants, and one with fluid in both upper quadrants and in one of the paracolic gutters. Further evaluation revealed a total of 24 injuries (five liver, four spleen, two intraperitoneal bowel, seven mesentery, one duodenum, one extraperitoneal bladder, four adrenal gland) in 15 patients, as confirmed with findings from 15 CT examinations, two cystographic examinations, five laparotomies, and one autopsy. Three of the injury sites (one bladder, one liver, and one spleen) were predicted with the use of US on the basis of parenchymal or organ contour abnormalities.

The remaining 11 patients in this group had a benign outcome with no abdominal injuries, as confirmed in 10 patients with findings from nine CT examinations, one repeat US, and one DPL. In these cases, the sonographic fluid usually represented fat or bowel at follow-up studies.

Fluid in Both the Pelvis and Abdomen
Twenty-two patients (mean age, 34 years; age range, 17–57 years) had fluid in the pelvis and abdomen. All 22 had fluid in one or both upper quadrants, and 10 also had fluid in one or both paracolic gutters. Within the pelvis, fluid was isolated to the CDS and contiguous recesses in eight patients, extended from the CDS into the SVS in nine patients (Fig 4), and was isolated to the SVS in five patients.



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  		Figure 4a. (a) Longitudinal transabdominal US image of the pelvis in a 24-year-old woman depicts a small amount of anechoic fluid (curved arrow) in the CDS adjacent to hyperechoic bowel (bo). In addition, some fluid extends superiorly over the uterine fundus and bladder dome and into the SVS (straight arrows). (b) Transverse contrast-enhanced CT image of the upper abdomen reveals extensive liver laceration (arrows).

 


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  		Figure 4b. (a) Longitudinal transabdominal US image of the pelvis in a 24-year-old woman depicts a small amount of anechoic fluid (curved arrow) in the CDS adjacent to hyperechoic bowel (bo). In addition, some fluid extends superiorly over the uterine fundus and bladder dome and into the SVS (straight arrows). (b) Transverse contrast-enhanced CT image of the upper abdomen reveals extensive liver laceration (arrows).

 
Further evaluation revealed a total of 36 injuries (seven liver, seven spleen, nine bowel, five mesentery, one intraperitoneal bladder, one pancreas, two kidney, two adrenal gland, two retroperitoneal hemorrhage) in 19 patients, as confirmed with findings from 14 CT examinations, one cystographic examination, 14 laparotomies, and one autopsy. Ten of the injury sites (five spleen and five liver) were predicted with the use of sonography on the basis of parenchymal irregularities. In the 19 injured patients, the pelvic collections (presumably representing pelvic hemoperitoneum) ranged from 5 mm to 9 cm in depth, with a mean of 29 mm ± 18; in 14 (74%), they were between 2 and 4 cm, and in 10 (53%), they were at least 3 cm. Four of the pelvic collections also contained complex components with debris or septations.

The other three patients with fluid in the pelvis and abdomen had no injuries. Two had clinical and sonographic stigmata of cirrhosis and portal hypertension and were followed up clinically, with a good outcome. The third was a 40-year-old woman with a 1-cm pocket of fluid in the CDS and a questionable sliver of fluid in the right upper quadrant. Follow-up CT demonstrated low-attenuating fluid (likely physiologic) in the CDS and a fluid-filled bowel loop, not free fluid, in the right upper quadrant, without evidence of injury.

Statistical Analysis
The results of statistical comparison of the five groups are summarized in Table 3. Results of a global exact test performed to determine if differences existed in the rates of injury and laparotomy according to patient group revealed statistically significant differences (P < .001) and allowed pairwise comparisons to be made. Patients with anechoic fluid isolated to the CDS and contiguous recesses (group 2) had significantly similar injury (4.0% vs 0.8%, P > .05) and laparotomy (2.0% vs 0.3%, P > .05) rates compared with patients with no fluid (group 1). Patients with fluid isolated to the SVS (group 3) had injury (0%, P > .05) and laparotomy (0%, P > .05) rates that were significantly similar to those of group 1 and group 2 patients, but the small sample size (n = 4) likely provided inadequate power to detect differences. Patients with fluid in the upper abdomen (group 4) and patients with fluid both in the pelvis and abdomen (group 5) had significantly higher injury (58% and 86%, respectively) and laparotomy (19% and 64%, respectively) rates, compared with those of either group 1 or group 2 patients (with P values ranging from .001 to .02 for the various comparisons) (Table 3). Physiologic pelvic fluid collections were significantly smaller in depth than traumatic pelvic collections (P < .001), even when the largest traumatic collection (which at 9 cm was more than three SDs above the mean) was excluded (P < .001).


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  		TABLE 3. Relation of Fluid Location to Abdominal Injury and Laparotomy Rates
 
With the criteria specified in this study, US findings were positive for injury in 39 (sensitivity, 89%; 95% CI: 79%, 98%) of the 44 injured patients (Table 4). Of the 39 true-positive findings identified with US, 32 were detected on the basis of intraperitoneal fluid, two on the basis of combined intra- and extraperitoneal fluid, and five on the basis of isolated extraperitoneal abnormalities. There were five false-negative, 25 false-positive, and 978 true-negative findings. False-positive findings usually occurred when fluid or parenchymal abnormalities depicted with US could not be confirmed with ancillary tests, or when ancillary test findings suggested nontraumatic causes for the sonographic findings. False-negative findings usually occurred when injuries were not associated with significant hemoperitoneum. Overall, the specificity was 98% (95% CI: 96.5%, 98.4%), accuracy was 97% (95% CI: 96%, 98%), positive predictive value was 61% (95% CI: 49%, 73%), and negative predictive value was 99% (95% CI: 99.0%, 99.9%) (Table 4). Seventy-three patients who underwent follow-up CT, repeat US, or surgery and those who died and were examined at autopsy had fluid somewhere in the abdomen and pelvis at screening US. In 58 patients, the cause of fluid was confirmed to be traumatic in 34 patients and physiologic in 24 patients. Hence, the positive predictive value for fluid as opposed to injury was 79% (95% CI: 70%, 89%). The likelihood ratios of positive and negative test findings were 35.6 and 0.12, respectively. A likelihood ratio greater than 10 for positive findings or a likelihood ratio less than 0.1 for negative findings have been interpreted (25) as having a potentially substantial effect on clinical decision making.


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  		TABLE 4. Assessment of Screening US
 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
REFERENCES
 
These study findings suggest that US is an effective screening tool for blunt abdominal trauma in female patients of reproductive age. Because more than 89 (8%) of 1,047 patients (only one of whom subsequently underwent CT) in our study population were pregnant at the time of screening, the ability to objectively evaluate the abdomen without the use of ionizing radiation was of great benefit. By using our hypothesis that anechoic fluid isolated to the CDS and adjacent recesses is physiologic in this population, the sensitivity, specificity, and accuracy were 89%, 98%, and 97%, respectively. If fluid in the CDS had been considered positive, the sensitivity would have been 91% (95% CI: 82%, 98%) and the specificity, 92% (95% CI: 90%, 94%). The positive predictive value of US for the detection of injury was 61%, which compares unfavorably with that documented or calculated from the data reported in other articles (1,3–5,7,8,10–12,14).

One of the reasons for the relatively low positive predictive value in our institution is that we regard any potential abnormality as an indication for further diagnostic evaluation. Hence, scans that depicted questionable fluid were considered false-positive, even if the findings were prospectively interpreted as being likely artifactual. Moreover, because the aim of screening US is to depict injury as opposed to fluid, we counted findings in those cases in which nontraumatic ascites was confirmed with follow-up tests as false-positive, and we counted findings in those cases in which physiologic fluid was confirmed as true-negative. Because previous authors (1–14) have considered these findings to be true-positive even in the absence of injury, we recalculated the positive predictive value for fluid and obtained a value of 79%.

Of 1,047 female patients of reproductive age with trauma, 56 (5.3%) had anechoic sonographic fluid isolated to the CDS. We compared patients in this group with patients with no fluid and found that they had significantly similar injury and laparotomy rates. On the other hand, these patients had injury and laparotomy rates that were significantly lower than those of patients with fluid elsewhere (fluid isolated to the abdomen or fluid both in the pelvis and abdomen).

Physiologic fluid within the CDS was described in the surgical and obstetric literature in 1922 (15) and 1931 (16) and in the radiology literature in 1979 (24) and 1986 (21). The mechanism of fluid accumulation is unclear and is probably multifactorial (17,19–21,26). With transabdominal imaging, physiologic fluid has been described (21,24) during all stages of the menstrual cycle in up to 30%–40% of healthy volunteers. To our knowledge, the volume of physiologic fluid as depicted with transabdominal scanning has not been assessed. In the obstetric literature, numerous authors (19,20,22,23) have quantified the volume of fluid found surgically in the CDS and have estimated the upper limit of physiologic fluid at about 45 mL. Although these authors describe the fluid as ranging from clear to blood-tinged, physiologic fluid is generally anechoic on sonographic images. When fluid in the CDS contains internal echoes, it is unlikely to be physiologic (27–31), and in the patient with trauma, this fluid likely represents hemoperitoneum.

Endovaginal US is generally superior in the assessment of fluid within the CDS because it depicts smaller quantities of fluid, it can differentiate fluid from adjacent bowel loops, and it more clearly defines the appearance of the fluid (26,32–35). In our study, supplementary endovaginal scanning was beneficial on two separate occasions in documenting anechoic fluid within the CDS after the initial screening US showed questionable echoes. Because the injury rate for patients with isolated fluid in the CDS is so low, however, we do not recommend routine endovaginal sonography for further evaluation of pelvic fluid in the absence of other clinical or imaging findings.

To our knowledge, the anatomic location of physiologic fluid also has not been rigorously characterized. Typically, physiologic fluid is described in the CDS and adjacent recesses. In 1984, Forsby and Henriksson (36) showed that as little as 10 mL of fluid instilled into the CDS at salpingography may become sonographically visible in the hepatorenal recess with patient positioning. However, their finding has not been confirmed clinically; we recommend that even small quantities of fluid outside the CDS be regarded as being suggestive of injury that requires further work-up.

Because the CDS is the most dependent recess in the peritoneum in both the supine and upright positions, pathologic fluid tends to collect within it (37). In our study, 20 (57%) of 35 patients with traumatic hemoperitoneum had fluid in the pelvis; however, except for the patient with the bladder dome laceration, all also had fluid in the upper abdomen. Fluid in the CDS was never the sole manifestation of a solid organ or enteric injury.

Traumatic pelvic collections were statistically larger (mean anteroposterior dimension, 2.9 cm) than physiologic collections (mean, 1.3 cm). Fifty-three percent of traumatic collections were at least 3 cm, whereas only 4% of physiologic collections exceeded the same threshold. Traumatic collections also tended to occupy more pelvic recesses and frequently involved the SVS, whereas physiologic fluid did not extend over the bladder dome. In addition, the pelvic fluid was complex in four of 19 patients, with hemoperitoneum involving the abdomen and pelvis. Two patients in our series had focal collections anterior to the bladder that represented extraperitoneal bladder extravasation on cystography. On the basis of these observations, complex fluid within the CDS, pelvic fluid at least 3 cm in depth, fluid extending into the SVS, or fluid loculated anterior to the bladder should be considered with suspicion.

In this study, we arbitrarily considered female patients between the ages of 10 and 60 years to be of reproductive age. However, the actual age range of patients in the physiologic fluid group was 15–54 years. Had we chosen this as our age range, there would have been 968 patients in the study, and the sensitivity and specificity would have been 90% (95% CI: 81%, 98%) and 98% (95% CI: 97%, 99%), respectively. Since reproductive years are highly variable among women, it would be beneficial to obtain each patient’s menstrual and reproductive history at the time of resuscitation, if possible.

One important assumption made by us and by others (2–12) is that patients with a benign clinical outcome have no injuries. In 904 patients, the clinical suspicion of abdominal injury was sufficiently low that no imaging or surgical procedures were performed after the initial negative screening US finding. Patients were admitted for observation, many of them with continuous hemodynamic monitoring, prior to discharge. No complications of missed abdominal injury were identified at follow-up visits in the clinic, or in systematic monthly audits of all trauma centers in the county.

In conclusion, our study findings show that, in female patients of reproductive age with blunt trauma, small amounts of anechoic fluid isolated to the CDS and/or adjacent pelvic recesses should be considered physiologic; this fluid does not require further evaluation or intervention in the absence of other radiologic or clinical findings. On the other hand, (a) if the fluid measures at least 3 cm in depth, contains internal echoes, extends into the SVS, or is loculated anterior to the bladder; (b) or if the patient is known to be past her reproductive years; or (c) if the patient’s reproductive status is unknown, fluid in the pelvis should be regarded with suspicion. In particular, gross hematuria mandates assessment with additional studies (5,8). In questionable cases, endovaginal scanning may be beneficial to better characterize the pelvic fluid. Finally, even if no fluid is present, suspicious parenchymal irregularities should be evaluated further because they may indicate clinically important disease.


   ACKNOWLEDGMENTS
 
The authors express their gratitude to Joan Garcia, BSN, Linda Richards, MN, Dale Fortlage, BA, and Kathleen Shepherd, MA, for their important contributions.


   FOOTNOTES
 
Abbreviations: CDS = cul-de-sac, DPL = diagnostic peritoneal lavage, SVS = supravesical space

Author contributions: Guarantor of integrity of entire study, C.B.S.; study concepts, all authors; study design, C.B.S., M.A.B., G.C.; definition of intellectual content, C.B.S., G.C.; literature research, C.B.S.; clinical studies, C.B.S., G.C., M.A.B., E.J.B., N.P.; data acquisition, C.B.S., M.A.B., G.C., N.P., E.J.B.; data analysis, R.D., C.B.S., M.A.B., G.C., N.P.; statistical analysis, R.D., C.B.S.; manuscript preparation, C.B.S.; manuscript editing, G.C.; manuscript review and final version approval, all authors.


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TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
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