DIAGNOSIS of INCISIONAL HERNIA: DYNAMIC ULTRASOUND versus CT

Femoral hernias, Henry Robert Whalen, Gillian A Kidd, Patrick J O’Dwyer

BMJ2011;343doi: http://dx.doi.org/10.1136/bmj.d7668(Published 8 December 2011)

Cite this as:BMJ2011;343:d7668

 

An overweight 65 year old woman visits her general practitioner with discomfort in her right groin. On examination, the suggestion of a reducible groin lump is noted. She is routinely referred to the surgical outpatient clinic with a possible diagnosis of inguinal hernia. However, two weeks later and before her surgical appointment, she again visits her general practitioner, this time with vomiting, diarrhoea, and colicky abdominal pain. She is immediately referred to the emergency department. An abdominal radiograph shows small bowel obstruction. She is admitted to the surgical ward with a diagnosis of obstructed femoral hernia and has a small bowel resection and emergency hernia repair.

What is a femoral hernia?

A femoral hernia is the protrusion of a peritoneal sac through the femoral ring into the femoral canal, posterior and inferior to the inguinal ligament. The sac may contain preperitoneal fat, omentum, small bowel, or other structures.

How common are femoral hernias?

·         About 5000 femoral hernia repairs are carried out in the United Kingdom each year

·         Femoral hernias account for a fifth of all groin hernias in females but less than 1% of groin hernias in males

·         The 40% of femoral hernias that present acutely are associated with a 10-fold increased risk of mortality1 2

Why is a femoral hernia missed?

Evidence is scarce as to the reason why femoral hernias are often missed and present as emergencies. Patients may be aware of groin discomfort or a groin lump, but they may not realise its clinical importance and may be reluctant to seek medical help. Initially some patients present to primary care with vague symptoms including groin discomfort that may be attributed to other disease such as osteoarthritis. As femoral hernias are typically small, they may be easily missed on examination, particularly in obese patients. Furthermore, owing to the difficulty in clinically distinguishing groin hernias, femoral hernias may be mistaken for inguinal hernias and referred for surgical opinion on a non-urgent basis.3

In an emergency, patients may present with signs of bowel obstruction, which include colicky abdominal pain, vomiting, and abdominal distension. About a third of patients do not complain of symptoms directly attributable to a hernia,4 and a groin lump is not always present. Other diagnoses, such as gastroenteritis, enlarged groin lymph node, diverticulitis, or constipation, may be made in error.⇓

Inguinal hernias are usually reducible and above the inguinal ligament. Femoral hernias are often irreducible and below the inguinal ligament. Adapted with permission from Ellis H. Clinical anatomy. 6th ed. Blackwell Scientific, 1977

Retrospective studies have observed that about 40% of hernias causing symptoms of acute bowel obstruction are missed owing to a lack of groin examination.5 6 The researchers concluded that female patients and all patients with femoral hernia were less likely to have a groin examination, despite signs of bowel obstruction being noted.5

Why does this matter?

Although femoral hernias are less common than inguinal, they are associated with higher rates of acute complication. The cumulative probability of strangulation for femoral hernias is 22% three months after diagnosis, rising to 45% 21 months after diagnosis, whereas the probability of strangulation for an inguinal hernia is 3% and 4.5% respectively over the same time period.7

Several studies have shown that acute femoral hernias and their subsequent complications are associated with increased morbidity and mortality.1 2 8 9 10 Examples of morbidity resulting from acute presentation include increased rates of bowel resection, wound infection, and cardiovascular and respiratory complications.10 As elective femoral hernia repair has been shown to be a relatively safe procedure (even in patients aged over 80), it is generally accepted that femoral hernias should be referred urgently and repaired electively.2 10 11 12

Missed femoral hernia at emergency presentation delays time to surgery.5 One study has shown an increased likelihood of bowel resection if surgery is undertaken more than 12 hours after the onset of acute symptoms.13 Preoperative delay is clearly linked with an increase in bowel resection, and this is associated with mortality rates that are about 20 times higher than those for patients having elective hernia repair (which would not require a bowel resection).2

How is it diagnosed?

Clinical

Classically, femoral hernias present as mildly painful, non-reducible groin lumps, located inferolateral to the pubic tubercle. In contrast, inguinal hernias are found superomedially. However, femoral hernias tend to move superiorly to a position above the inguinal ligament, where they may be mistaken for an inguinal hernia. Differentiation of groin hernias on clinical grounds is therefore unreliable, irrespective of the experience of the examining doctor.14 In patients presenting electively, only about 1% of groin hernias in males are likely to be femoral, whereas the likelihood in females is about 20%.1 Clinical examination alone is inaccurate in differentiating groin hernia.14 Therefore in females, owing to the greater prevalence of femoral hernia, consider all groin hernia to be femoral until proved otherwise.

Femoral hernias may also present without a palpable lump and with only vague symptoms of abdominal or groin pain. However, symptoms may vary and there is a lack of evidence to predict the likelihood of a particular symptom indicating the presence of a femoral hernia. Patients may present later with clinical features of bowel obstruction. Undertake a detailed groin examination in all patients presenting with bowel obstruction.

Investigations

Ultrasonography, magnetic resonance imaging, and computed tomography (CT) have all been shown to be accurate in detecting and differentiating groin hernias.

Ultrasonography is widely available, non-invasive, and highly accurate in differentiating inguinal from femoral hernia—with sensitivities and specificity of 100% being reported in two studies.15 16 Its accuracy is, however, operator dependent.

Magnetic resonance imaging has been reported to be more accurate than ultrasonography in detecting inguinal hernia.17 However, there is a lack of evidence for whether magnetic resonance imaging is better than ultrasonography in detecting and differentiating groin hernia. Therefore ultrasonography should be the first choice for electively investigating suspected groin hernia as it is more widely available, less costly, and accurate.

CT scanning has been shown to be accurate in differentiating groin hernias. One retrospective study reports the correct identification of 74 of 75 hernias (28 femoral and 47 inguinal), which were later confirmed at operation.18 This is broadly comparable with the non-invasive modalities outlined above, but as there is a substantial radiation dose associated with CT scanning, it should not be used electively for investigating suspected groin hernia. In the acute abdomen, however, consider CT as the first choice for investigating suspected small bowel obstruction in the presence of a negative clinical examination.

How is it managed?

In males, a groin hernia suspected as being femoral on clinical examination requires urgent referral, due to the risks of acute complications outlined above. All groin hernia in females should be urgently referred for assessment.

Electively, both open and laparoscopic repair using mesh have significantly lower recurrence rates than repair using sutures only.1 Open repair has the advantage that it can be performed under local anaesthetic. No evidence suggests superiority of either method in the acute setting.

Some research has suggested that femoral hernias may be overlooked during repair of suspected inguinal hernias.19 So during surgical repair of all groin hernias examine the femoral canal if an obvious inguinal hernia is not observed.

Key points

·         Femoral hernias are more common in females and in people aged over 65 years and are associated with higher rates of complications such as strangulation

·         Emergency surgery for femoral hernia is associated with a 10-fold increased risk of mortality, which is further increased by preoperative delays

·         Clinical examination is unreliable in differentiating femoral from inguinal hernia

·         Refer all females with groin hernia for urgent assessment and management

·         Examine the groins of all patients presenting with signs of small bowel obstruction

·         Ultrasound is the first line elective investigation for suspected uncomplicated groin hernia, but in acute small bowel obstruction, CT scanning is first choice

 

ULTRASOUND for DIAGNOSIS of SKULL FRACTURES in CHILDREN

Accuracy of Point-of-Care Ultrasound for Diagnosis of Skull Fractures in Children, Joni E. Rabiner, Lana M. Friedman, Hnin Khine,  Jeffrey R. Avner,  and James W. Tsung

Abstract

OBJECTIVE: To determine the test performance characteristics for point-of-care ultrasound performed by clinicians compared with computed tomography (CT) diagnosis of skull fractures.

METHODS: We conducted a prospective study in a convenience sample of patients ≤21 years of age who presented to the emergency department with head injuries or suspected skull fractures that required CT scan evaluation. After a 1-hour, focused ultrasound training session, clinicians performed ultrasound examinations to evaluate patients for skull fractures. CT scan interpretations by attending radiologists were the reference standard for this study. Point-of-care ultrasound scans were reviewed by an experienced sonologist to evaluate interobserver agreement.

RESULTS: Point-of-care ultrasound was performed by 17 clinicians in 69 subjects with suspected skull fractures. The patients’ mean age was 6.4 years (SD: 6.2 years), and 65% of patients were male. The prevalence of fracture was 12% (n = 8). Point-of-care ultrasound for skull fracture had a sensitivity of 88% (95% confidence interval [CI]: 53%–98%), a specificity of 97% (95% CI: 89%–99%), a positive likelihood ratio of 27 (95% CI: 7–107), and a negative likelihood ratio of 0.13 (95% CI: 0.02–0.81). The only false-negative ultrasound scan was due to a skull fracture not directly under a scalp hematoma, but rather adjacent to it. The κ for interobserver agreement was 0.86 (95% CI: 0.67–1.0).

CONCLUSIONS: Clinicians with focused ultrasound training were able to diagnose skull fractures in children with high specificity.

Ultrasound Technique

Before the start of the study, all enrolling PEM attending and fellow physicians attended a 30-minute didactic session to learn how to use ultrasound to evaluate the skull for fracture and to standardize the method in which bedside ultrasound was performed by participating physicians, followed by a 30-minute hands-on practical session.

A reference manual complete with instructions and images was available throughout the study. All study sonologists except for one were novices to musculoskeletal ultrasound at the start of the study. We defined an experienced sonologist as having performed egal or more 25 musculoskeletal ultrasound examinations, which is the minimum recommended number of scans for ultrasound credentialing per American College of Emergency Physicians Emergency Ultrasound Guidelines.

SonoSite ultrasound systems (SonoSite Inc, Bothell, WA) with high-frequency linear transducer probes (10–5 MHz) were used to perform focused ultrasound examinations to evaluate for skull fracture. Ultrasound gel was layered onto the ultrasound probe, and then the probe was lightly applied to the scalp to avoid pressure on the injured skull. The transducer was placed over the area of soft tissue swelling, hematoma, point of impact, or point of maximal tenderness (Fig 1). Scans were performed in 2 perpendicular  planes, and still pictures and video clips were recorded in each orientation. Skull suture lines were differentiated from skull fractures by following suspected sutures to a fontanelle. If a suspected fracture crossed a suture line or fontanelle, the contralateral area on the skull was imaged for comparison.

The sagittal, coronal, and metopic sutures can be traced to the anterior fontanelle, and the lambdoid sutures can be traced to the posterior fontanelle. The squamous sutures, however, may be difficult to follow to an open fontanelle, but sonologists were encouraged to scan the contralateral area of the skull for comparison. A diagram of suture anatomy was included in the study reference manual.

DISCUSSION

We have demonstrated in the largest cohort of patients to date that with a 1-hour, focused musculoskeletal ultrasound training session, novice sonologists are able to quickly and accurately diagnose skull fractures with high specificity. Previous data on ultrasound by radiologists for skull fracture diagnosis revealed high accuracy.17,20 In addition, studies of ultrasound by clinicians with focused training have also revealed rapid and accurate diagnosis of skull fractures with point-of-care ultrasound. 15,18,19 In our study, as with most ultrasound applications, the specificity was higher than the sensitivity (Table 3).

Clinical assessment may not be completely reliable for predicting skull fractures and intracranial injuries in children. 24 In our data, 2 of 39 (5%)patients assessed to have a 2% to 25% likelihood of fracture and 3 of 9 (33%)assessed to have a 26% to 50% likelihood of fracture after obtaining the history and physical examination had confirmed skull fractures (Table 2). In addition, of the 4 patients in our study who had reported palpable skull fractures on physical examination, only 2 (50%) had confirmed skull fracture by CT scan.

In current practice, head CT serves as the gold standard diagnostic test to evaluate for skull fractures and intracranial bleeding after head trauma. However, there are several advantages of using point-of-care ultrasound in the detection of skull fractures. First,ultrasound can be performed rapidly, which can allow earlier detection of skull fracture as a marker for suspected intracranial injury and neurosurgical consultation. Second, point-of-care ultrasound has the potential to reduce CT use and ionizing radiation exposure in children. The estimated lifetime risk of cancer froma head CT is substantially higher for children than for adults because of a longer latency period and the greater sensitivity of developing organs to radiation. 4–7 However, intracranial injury may occur without skull fracture, and clinicians must use clinical judgment or decision rules25–28 for obtaining CT scan regardless of the presence or absence of skull fracture. In addition, ultrasound can also be performed in young children without the need for sedation.

Point-of-care ultrasound for skull fracturesmay be especially useful in places without access to CT scan. It has been estimated by the World Health Organization that up to two-thirds of the world’s population does not have access to diagnostic imaging technology, 29 and portable ultrasound may be mplemented in these resource-scarce locations.30 In addition, ultrasound may be useful for triage in mass casualty disasters31 or in austere environments.32 Last, ultrasound may be used in pediatricians’offices or in urgent care centers for patients with suspected isolated skull fracture without ready access to CT scan.

Ultrasound may diagnose minimally or nondisplaced skull fractures that can be missed on CT scan. Recent research has revealed that ultrasound has superior sensitivity to radiography in certain types of fractures, 33 and it has been shown to detect nondisplaced fractures as small as 1 mm. 34 Our study included a case of a 16-year-old male who presented with a boggy frontal scalp hematoma after an assault. Skull ultrasound performed by a novice sonologist was interpreted as positive for fracture and confirmed on expert review (Fig 5B). The CT was read as negative for skull fracture, and the patient was discharged from the ED. On telephone follow-up, the patient was asymptomatic.

Knowledge of suture anatomy is essential in performing ultrasound examinations of infant skulls.18,19 A suture appears symmetric and regular and leads to a fontanelle, whereas a fracture is jagged andmay be displaced. All enrolling sonologists in our study were taught to differentiate sutures from skull fractures by following sutures to a fontanelle. If a suspected fracture crossed a suture or fontanelle, the contralateral area of the skull was imaged for comparison. No errors in our study were due to sutures. There have been several recent studies published on ultrasound for diagnosis of skull fractures in children that involved small sample sizes ofchildren. 15,18,19 Our study adds the largest cohort to the current literature. In addition, pooling our data with these similar studies to forma cohort of 185 patients reveals ultrasound to be highly sensitive and specific for diagnosing skull fractures in children (Table 4). The study by Weinberg et al 15 looked at fracture detection for all bones and included a small subset of patients with suspected skull fracture. In the study by Riera and Chen, 19 few enrolling sonologists with no formalized skull ultrasound training performed skull ultrasound. Parri et al 18 reported a very high prevalence of skull  fracture because they enrolled patients with localizing evidence of trauma. However, all of these studies used clinician sonologists who performed blinded point-of-care ultrasound imaging and compared skull ultrasound with CT as the reference standard. Skull ultrasound may be particularly useful in well-appearing patients with suspected isolated skull fracture on the basis of history and physical examination and low risk for clinically important traumatic brain injury. The question remains whether the absence of skull fracture on ultrasound in selected patients with head injury in the presence of single isolated risk factors for intracranial bleeding can obviate the need for CT scan. Two children in our study, one with isolated scalp hematoma and another with isolated loss of consciousness, had no skull fracture detec ted on ultrasound or CT scan but were subsequently found to have intracranial hemorrhage. Thus, caution is warranted in using ultrasound to rule out intracranial injury, and additional research is needed to fully answer this question.

Our study has several limitations. Our study population consisted of a convenience sample of patients enrolled when a trained physician was available,but the prevalence of skull fractures of 12% in our study is similar to other studies. 15,19,24 Ultrasound is an operator-dependent modality, but because a novice group of sinologists was trained to performskull ultrasound with such high specificity, we believe that our results may be generalizable to other clinicians with focused training. Last, there was a limitation in our ultrasound scanning technique. Our only false-negative result was due to a skull fracture that was adjacent to but not directly beneath the scalp hematoma,and therefore this fracture was missed on ultrasound but confirmed on CT scan(Fig 4). We now recommend scanning the areas around the scalp hematoma if a skull fracture is not visualized directly beneath it, similar to the method proposed by Riera and Chen.19

CONCLUSIONS

Clinicians with focused, point-of-care ultrasound training were able to diagnose skull fractures in children with head trauma with high specificity and high negative predictive value. In addition, almost perfect agreement was observed between novice and experienced sonologists. Pooled analysis of published studies for skull fracture reveals high specificities with variable sensitivities. Future research is needed to determine if ultrasound can reduce the use of CT scans in children with head injuries.

Ultrasound for Diagnosis of Skull Fractures and reduction of ionizing radiation exposure,     Niccolo Parri, Liviana Da Dalt, University of Padova, Department of Pediatrics, Treviso, Italy

To the Editors, We read with interest the paper by Rabiner et al.(1). They demonstrated, in the largest cohort ever reported, the high sensitivity of ultrasound (US) for the diagnosis of skull fractures (SF). Their results seem to be particularly useful for everyday practice because head US have been performed by many unexperted sonographers. However the study seem to suffer from some limitations that, may question the validity of results and conclusions. There is no question that ionizing

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To the Editors, We read with interest the paper by Rabiner et al.(1). They demonstrated, in the largest cohort ever reported, the high sensitivity of ultrasound (US) for the diagnosis of skull fractures (SF). Their results seem to be particularly useful for everyday practice because head US have been performed by many unexperted sonographers. However the study seem to suffer from some limitations that, may question the validity of results and conclusions. There is no question that ionizing radiation exposure in children must be reduced and that US has the potential to reduce it. The authors enrolled a convenience sample of patients < 21 years who underwent a CT because of a head trauma and/or suspected SF based on the decision of the treating physician. It would be worthwhile to state more explicitly that some clinical practice guidelines recommend imaging with CT for head-injured children whose only risk factor is SF. Since the reduction of CT can be obtained by identifying children at very low risk of clinically important traumatic brain injuries (ciTBI), we have concerns about the methods proposed in the article. The Pediatric Emergency Care Applied Research Network (PECARN) derived and validated a high-quality, well-performing clinical prediction rule for identifying children < 18 years at very low risk of ciTBI for whom CT could be obviated.(2) The rule might not be perfect, but represent the best current scientific evidence. PECARN as well as multiple prior studies have considered scalp findings to be a risk factor for children < 2 years. For older children the only signs of basal skull fractures give a higher risk for ciTBI.(2) The authors enrolled 69 patients discovering 8 SF (12%) in children < 21 years; without any information about the patients for whom SF probably have the most diagnostic importance as predictors of intracranial injury there is a concern that some of the older patients could probably had underwent a CT scan only for the suspicious of SF. The Authors found 8 (12%) SF on 69 patients with external signs of head trauma (soft tissue swelling/hematoma, point of impact/maximal tenderness). A general higher incidence of SF is reported in the younger age group. Moreover, the presence of scalp hematoma is 80%-100% sensitive for an associated SF since most fractures have an overlying hematoma or soft tissue swelling (>90%).(3) Therefore there's concern regarding the possibility of a unacceptable interobserver agreement in the assessment of physical examination findings in children with blunt head trauma. Finally, since this is a comparative study we think that a blind expert should have reviewed both ultrasound and CT images for the 2nd false positive patient. The authors correctly report a higher sensitivity for radiology, since it can detect non-displaced fractures as small as 1 mm. Even though one more true positive patient would have a small contribution to increase the sensitivity and specificity of the test, this would have strengthen the test since the other 2 missed patients can be ascribed to errors on the US technique.