Abdominal Trauma — Blunt & Penetrating: FAST-First Triage, CT Limits, Selective Non-operative Management and Primary Repair

Thirty-year-old restrained driver, 90 km/h impact, lap-belt bruise curving above the iliac crests, blood pressure 118, heart rate 104, FAST positive in Morrison's pouch, CT shows free fluid without solid-organ injury and a transverse abdominal-wall contusion. Admit and watch, or open now? The examiner wants the seat-belt position likelihood, what free fluid means for hollow viscus risk, which CT signs you trust and which you do not, and what score flags the bowel injury CT cannot see. This page answers each with the number from the paper beside it.^{[4][10][11][12]}

Overview & Definition — mechanism sets the pathway

Abdominal trauma divides by mechanism into blunt injury and penetrating injury, with penetrating further split into stab wounds and gunshot wounds — and each changes the diagnostic pathway from the first minute.^[16][21] For stable anterior abdominal stab wounds, selective management is now the worldwide gold standard rather than mandatory laparotomy.^[16] The supporting toolkit is explicit: clinical follow-up, local wound exploration with or without diagnostic peritoneal lavage, diagnostic laparoscopy, and abdominal CT — choose among these by stability and findings, not by habit.^[16] For gunshot wounds the same selective discipline now applies: roughly a third of patients with abdominal gunshot wounds can be managed non-operatively, and programmes running selection with CT and observation drive non-therapeutic laparotomy below 10 percent.^[21]

The blunt story is a deliberate reversal. In blunt solid-organ injury the shift from routine surgery to observation in stable patients, carried by modern imaging, ran rapidly from the 1980s onwards.^[3] Today the review position is observation-first even for high-grade injuries, with interventional angiography widening rather than narrowing the non-operative pool.^[2] The liver anchors the epidemiology: it is the most commonly injured abdominal solid organ regardless of mechanism, most injuries are grades I to III, and 12 to 20 percent are grades IV and V.^[1]

Epidemiology & Risk — who bleeds, who perforates, who is missed

Liver first, bowel most feared, diaphragm most missed. Blunt liver grades IV and V are the minority at 12 to 20 percent yet drive the operative and embolisation workload.^[1] Significant blunt bowel and mesenteric injury is uncommon — 3.3 percent after road crashes in the Swiss cohort, 3.1 percent in its sister cohort — but 18 to 24 percent of those injuries are diagnosed more than 24 hours late.^[8][9] Diaphragmatic injury is rare and elusive: 10 to 15 percent of penetrating thoracoabdominal injuries and 1 to 8 percent of blunt ones, with more than 62 percent initially undiagnosed.^[31] Rectal injury concentrates in young men after penetrating trauma — 88 percent male, median age 29, 80 percent penetrating in the South African series, with 31 extraperitoneal, 14 intraperitoneal and 5 combined injuries among 50 treated.^[40] Gunshot selection skews to the less injured: New England selective patients carried median ISS 16 versus 8 for immediate laparotomy.^[23]

Age shifts the stakes without changing the injury rate. Older belted patients sustained hollow viscus injury at a statistically similar rate to younger ones (5.5 versus 9.8 percent) yet died more often (5.5 versus 1.1 percent) and stayed longer — vigilance, not a different operation, is the adjustment.^[15]

Pathophysiology — contamination and delay, not memorised forces

What kills in abdominal trauma is bleeding first and missed hollow viscus injury second. Penetrating injury carries a high likelihood of intestinal injury, especially colonic, and the combination of haemorrhage, transfusion immunosuppression and enteric contamination sets the infection risk that short-course antibiotics address.^[34] Blunt bowel injury punishes delay: deferred recognition worsens prognosis, yet no single CT feature predicts it, which is why scores and serial examination exist.^[7] A missed diaphragm behaves as a time bomb rather than a static defect — delayed herniation with obstruction or perforation carries mortality as high as 85 percent, so diagnosis mandates repair.^[32] Link the physiology next door rather than re-owning it: uncontrolled abdominal bleeding feeds the lethal-triad physiology covered in the damage-control topics, and resuscitation ratios and transfusion clocks live there.^[1]

Presentation & the Seat-Belt Sign — position is the finding

Record the bruise against the anterior superior iliac spine, because position is the test. A seat-belt sign above the iliac spine carries a positive likelihood ratio of 4.2 for belt-related injury; at or below the spine the ratio is 1.5 — essentially uninformative — so routine abdominal imaging is reserved for the above-spine mark.^[12] CT depth refines the same finding: operative need reached 19.73 percent when the contusion sat above the spine on CT against 4.05 percent with clinical bruise alone, with more intra-abdominal injury above and more pelvic fracture below.^[14]

Free fluid is the CT finding that matters most. Among 754 belted patients the hollow viscus prevalence was 9.2 percent, and only one injured patient had a truly negative CT — free fluid carried a more than 40-fold increase in hollow viscus likelihood and was the best single classifier at AUC 0.87.^[11] In the 425-patient belted cohort, over a third had some intra-abdominal injury on CT yet only 13.6 percent required laparotomy, and the initial CT read 100 percent sensitive in that series — admit the bruise, trust a careful negative scan, and discharge only the stable with return precautions.^[13]

Missed Injuries & Differential — the three the scanner hides

Three injuries hide from the first assessment: the diaphragm, the blunt bowel, and the low-grade mesentery. The diaphragm is missed in seven scanned patients out of a small national series and in more than six in ten overall — keep it in the differential whenever the trajectory crosses the thoracoabdominal boundary, even with a negative CT and a normal chest film.^[31] At laparoscopy for thoracoabdominal penetration, nearly one in five diaphragmatic injuries came with a normal preoperative chest radiograph.^[26] Blunt bowel injury hides behind indirect signs: prospective 64-slice reports reached only 63.6 percent sensitivity with 79.6 percent specificity, and barely half of blunt bowel injuries were diagnosed before the operation.^[10] When CT is negative or equivocal, the differential stays open and the patient stays observed — no single CT characteristic predicts bowel injury on its own.^[7]

Scoring — ISS for triage, bowel scores for the watch, PECARN for children

Major trauma is conventionally marked at ISS above 15 with RTS below 7.84 marking major physiological derangement — the multicentre definition study tested exactly those cutoffs while proposing intervention-based triage as a better fit.^[35] TRISS remains the benchmarking survival model, built from the 1995 Major Trauma Outcome Study coefficients and now widely considered due for renewal.^[36] Quote scores for what they were built to do — triage monitoring and risk adjustment — never as permission to open or to close.

For the watched bowel, use a score when the scan equivocates. The Bowel Injury Prediction Score combines white-cell count, abdominal tenderness and CT mesenteric grade; in its derivation cohort a delay beyond 24 hours struck a quarter of stable scanned patients with significant injury.^[9] Head-to-head after road crashes, Faget, Raharimanantsoa and BIPS reached AUCs of 95.3, 89.2 and 87.6 percent for significant bowel and mesenteric injury — use any of them to select for early re-look or laparoscopy, not to discharge.^[8]

Children earn their own gate. The PECARN abdominal rule was derived to cut inappropriate CT in blunt paediatric trauma, defining the outcome that matters — injury needing acute intervention — as therapeutic laparotomy, embolisation, transfusion for abdominal bleeding, or two or more nights of intravenous fluids for pancreatic or gut injury.^[37][38] External validation found the very-low-risk criteria 99 percent sensitive, missing one child in 133 with clinically important injury — and that child had an extra-abdominal bleeding reason for transfusion.^[39] Clinically important injury itself is uncommon at 2.3 percent of scanned children.^[39]

FAST & eFAST — the rule-in triage tool

FAST answers one question at the bedside: is there free fluid to act on now. Across 75 studies and 24,350 patients, extended FAST detected intra-abdominal free fluid with 74 percent sensitivity and 98 percent specificity — 74 and 95 in hypotension, 76 and 98 in normotensive adults, 71 and 95 in children — with pneumothorax at 69 and 99 and pericardial fluid at 91 and 94 in the same analysis.^[4] The authors' verdict is the viva line: useful for ruling in, not supported as a rule-out tool.^[4] Cochrane agrees in plainer terms — high specificity but low sensitivity for visceral injury.^[5] In penetrating torso trauma the abdominal numbers sag further: pooled sensitivity 56 percent against specificity 96 percent, so ultrasound alone never clears a penetrating abdomen and must pair with CT or laparoscopy.^[6]

Run the unstable algorithm from those numbers. Positive FAST with hypotension goes to the operating room without further imaging; negative FAST with hypotension changes nothing and the search continues; stable patients go to contrast CT. The stable scan then carries the weight — which is why the next section prices CT's limits honestly.^[4][5]

CT — what it sees, what it misses, how to watch the gap

CT is the stable patient's test and the missed bowel's alibi. The commonest findings in proven blunt bowel injury are free fluid in 71.3 percent, free air in 43.6 percent and mesenteric infiltration in 23.4 percent — yet no single feature predicts injury significantly.^[7] Prospective reporting sensitivity sits at 63.6 percent with specificity 79.6, positive predictive value 53.9 and negative predictive value 85.5 percent — respectable for solid organs, unsafe for hollow viscus.^[10] Missed blunt cases showed mostly indirect signs, which is exactly what the equivocal scan looks like.^[10]

Watch the gap with protocol, not hope. Significant bowel injury complicates about 3 percent of crashes with nearly a fifth delayed beyond a day; scores above select for early diagnosis when the first scan equivocates.^[8] Strict observation with follow-up imaging for high-risk injuries, and restraint with repeat scans for low-risk ones, is the reviewed strategy — selection and monitoring minimise failure, and complications follow local expertise.^[2] For the belted patient specifically, a careful negative CT predicts absence of hollow viscus injury well enough to consider discharge of the stable with precautions — one missed injury in 754 in the multicentre cohort — but that decision belongs to a protocol, not a hunch.^[11][13]

Resuscitation — brief, because the numbers live next door

There is no debate that penetrating injury with peritonitis or haemodynamic instability goes urgently to laparotomy — that sentence opens the EAST penetrating guideline and it should open your answer too.^[18] Everything between instability and stability — ratios, permissive pressure, tranexamic timing, massive-transfusion triggers — is owned by the damage-control resuscitation and massive-transfusion topics; resuscitate by those protocols while the abdomen declares itself, and do not re-derive their numbers here.^[1]

Stab Wounds — select, scan, watch the clock

Stable anterior stab wounds without peritonitis or diffuse tenderness do not get routine laparotomy — that is the EAST practice-management position, built to minimise non-therapeutic operations without buying delay.^[18] The randomised proof is small but pointed: 51 patients, morbidity 19 percent after mandatory laparotomy against 8 percent with observation, 17 percent needing delayed operation, two days versus five in hospital, and about $2,800 saved per successful non-operative course.^[19] Modern prospective practice sharpens the clock: of 256 stabbed patients, 18 percent went straight to theatre for evisceration, instability or peritonitis, 83 percent of the remainder were selected for observation after near-universal CT, and only 2 percent failed — with the two hollow viscus failures declaring peritonitis at 10 and 20 hours.^[20] Watch for a full day before discharge; the failures announce themselves inside it.^[20]

Multiplicity does not change the plan: multiple anterior wounds carried no extra frequency or severity of intra-abdominal injury and no extra laparotomy or mortality in the two-centre series.^[16] Lower-resource practice concurs at scale: 20 studies with 1,505 initially observed stab patients, 245 ultimately operated, and zero reported mortality among those selected for observation — with CT increasingly guiding selection even where resources are thin.^[17]

Gunshot Wounds — selective, but narrower than stabs

Gunshot selection is real, newer, and stricter. The principles are patient selection, CT workup and clinical observation — applied that way, about a third of abdominal gunshots avoid operation.^[21] The meta-analytic record across 41 studies: nearly 30 percent selected for observation, 7.0 percent failure among stable patients without reduced consciousness or peritonitis, 0.4 percent mortality with selection, and over two-thirds of failures proving therapeutic at delayed operation.^[22] New England's ten-centre adoption curve tells the same story in practice: 23 percent selected, 8.4 percent failing at a mean 12.5 hours, complications concentrated in the immediate-operation group, and selection rising from 18 to 27 percent across the study era.^[23] Posterior wounds, peritonitis, instability and reduced consciousness stay operative — selection is for the stable, examinable anterior abdomen with a reassuring scan.^[22][23]

Laparoscopy — the peritoneal-breach arbiter

When the question is penetration rather than injury — did the stab cross peritoneum, is the diaphragm breached — laparoscopy answers without a full laparotomy. Across three urban centres and 510 stable penetrating patients, laparoscopy avoided laparotomy in 54.3 percent, delivered 26 fully therapeutic procedures, and held non-therapeutic laparotomy to 10.2 percent with 10 minor complications.^[24] Review ranges are wide with older equipment (sensitivity 66.7 to 100, specificity 33.3 to 100) and tighten toward 100 percent in modern series — select stable, examined patients and accept conversion for bowel suspicion.^[25] The diaphragm is laparoscopy's best yield: one in five thoracoabdominal penetrations without laparotomy indications carried a diaphragmatic injury, and nearly a fifth of those hid behind a normal chest film.^[26] The Cesena consensus now frames laparoscopy-first for emergency general surgery where skill and stability allow — trauma included.^[25]

Colon & Rectal Injury — repair most, divert the doomed, scope the rectum

Penetrating colon injury has moved from routine colostomy to repair. Five randomised trials found mortality no different between primary repair and diversion while total complications favoured repair at OR 0.28 with fewer infectious and wound complications.^[27] The AAST multicentre resection study concurs at scale: 297 patients, two-thirds anastomosed and one-third diverted, colon-related complications in 24 percent with no difference between strategies — while severe faecal contamination, transfusion burden and single-agent prophylaxis independently predicted complications and the repair-versus-diversion choice itself did not.^[28] Location does not rescue diversion either: right versus left colon showed no leak difference, so treat each injury on its merits against the patient's condition rather than its colonic postcode.^[29]

EAST codifies the low-risk lane: 37 studies screened with 16 meeting meta-analysis criteria across 705 low-risk randomised patients, recommending repair or resection-and-anastomosis over routine colostomy for civilian adults without shock, major bleeding, severe contamination or surgical delay.^[30] The rectum splits by peritoneum: mandatory proximal diversion for extraperitoneal injury with distal washout and presacral drainage omittable, against primary repair for intraperitoneal injury that behaves like colon.^[40]

Diaphragm — suspect by trajectory, confirm by looking

Suspect the diaphragm whenever a wound or force vector crosses the thoracoabdominal boundary. Penetrating rates run 10 to 15 percent with blunt at 1 to 8, yet most injuries are missed at first pass and CT misses them even in tertiary centres.^[31] Repair on finding: herniation with obstruction or perforation kills up to 85 percent, which converts every incidental diaphragmatic defect into an operative one.^[32] Laparoscopy is the confirmatory tool in the stable penetrated patient without other operative indications — a fifth positive, many with normal films.^[26]

Antibiotics — short, intravenous, then stop

Penetrating abdominal trauma prophylaxis is an agents-and-duration question answered only by randomised trials — no placebo-controlled trial of antibiotics versus nothing was ever found eligible, so every recommendation compares regimens, not treatment against none.^[33] The duration answer is 24 hours: 300 evaluable patients randomised to a day versus five days of intravenous cefoxitin showed no influence of duration on infection development and no difference in stay — give 24 hours of cover for the contamination found, then stop unless infection declares itself.^[34]

Blunt Solid-Organ NOM — the 85-percent doctrine with an angio backstop

Stable or prompt-responder blunt liver injury is observed regardless of grade in 85 to 90 percent of cases — grade describes the injury, stability decides the management.^[1] Angiography with embolisation rescues the blush and the fall, effective at stopping bleeding but priced in hepatic necrosis and sepsis — deploy it for contrast extravasation or instability-with-response, not as routine.^[1] Observation is active: strict monitoring with follow-up imaging for high-risk injuries, restraint for low-risk ones, multidisciplinary ownership, and selection discipline to hold failure down.^[2]

Special Populations — children gated by rule, elders watched harder

Children are imaged by rule, not reflex. Apply the PECARN abdominal criteria to identify the very-low-risk child in whom CT is avoided; the rule's derivation outcome — therapeutic operation, embolisation, transfusion, or prolonged fluids for pancreatic or gut injury — is the definition to quote.^[37][38] Validation holds the line at 99 percent sensitivity with clinically important injury in just over 2 percent of the scanned population.^[39] Older belted adults need the opposite adjustment: same hollow viscus rate as the young but fivefold mortality and longer stay, so admit, observe, and re-examine rather than trusting youth-calibrated reassurance.^[15]

Evidence, Guidelines & Regional Differences — who proved what

EAST owns penetrating selection: no routine laparotomy for stable stab wounds without peritonitis, and repair-over-stoma for low-risk colon injury — both practice-management guidelines, both quoted above with their numbers.^[18][30] Cochrane owns the two equipoise closures: primary repair beats diversion on complications without mortality difference across five colon trials, and penetrating-trauma antibiotics are RCT-compared regimens where 24 hours equals five days.^[27][33][34] The global South owns the scale proof for stab selection — 1,505 observed patients across 20 lower-resource studies with zero selection mortality.^[17] South Africa owns the rectal split and the colon-location counter-proof — diversion for extraperitoneal rectum, repair for intraperitoneal, and no anatomic excuse for stoma by colonic segment.^[29][40] Resuscitation, transfusion and open-abdomen doctrine are deliberately cited, not repeated, from the damage-control and massive-transfusion topics beside this one.^[1]

Exam Pearls — the one-liners that score

• Stable liver injury is observed in 85 to 90 percent regardless of grade — stability decides, grade describes.^[1]
• eFAST is 74 sensitive and 98 specific for free fluid: rules in, never out.^[4]
• Penetrating-abdomen ultrasound is 56 sensitive and 96 specific: never clears alone.^[6]
• CT reports catch 63.6 percent of bowel injuries and barely half the blunt ones: watch the equivocal scan.^[10]
• Free fluid means hollow viscus until proven otherwise: 40-fold odds, AUC 0.87.^[11]
• Above-spine bruise images and admits at LR 4.2; at-or-below at 1.5 does neither.^[12]
• BIPS combines white cells, tenderness and CT mesenteric grade; Faget leads the AUCs at 95.3.^[8][9]
• Stab selection fails in 2 percent of CT-selected modern practice, declaring at 10 to 20 hours — observe the full day.^[20]
• Gunshot selection holds a third of patients with 7 percent failure and 0.4 percent mortality.^[22]
• Laparoscopy avoids laparotomy in over half of stable penetrations with 10 percent non-therapeutic residue.^[24]
• Colon repair beats diversion on complications with equal mortality; segment never decides stoma.^[27][29]
• The diaphragm is missed in over six in ten and kills up to 85 percent when strangulated late.^[31][32]
• Twenty-four hours of antibiotics equals five days for penetrating contamination.^[34]
• PECARN very-low-risk misses one in 133 at 99 percent sensitivity — image the rest.^[39]

Revision summary

Mechanism splits the pathway, stability splits the decision. Observe stable blunt solid-organ injury with angio backup; select stable stabs and a third of gunshots with CT and a day of watching; scope the peritoneal question; repair colon and intraperitoneal rectum primarily while diverting extraperitoneal rectum; suspect the diaphragm by trajectory and repair on sight; stop antibiotics at 24 hours; gate children's scans by PECARN and watch belted elders harder. Every number above belongs to the paper cited beside it — quote the paper, not this page, at the viva.^{[1][18][21][27][34][39]}