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
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.
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.
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
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.
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
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.