Pediatric emergency medicine trisk 1125
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Hip
Acute onset of limp and refusal to bear weight are common presenting complaints
to the pediatric ED. In some patients, it can be difficult to localize the site of pain
and the differential diagnosis is broad. Point-of-care hip ultrasound is primarily
used to detect joint effusions and can be useful in the evaluation of pediatric
patients who present with limp or refusal to bear weight. Ultrasound is more
sensitive than radiographs for the detection of hip effusions in children and is
therefore suggested as the imaging modality of choice for the initial evaluation of
patients presenting with irritable hip.
Anatomy
With the patient lying supine, the femoral head can easily be identified and
appears as a round, hyperechoic structure with posterior shadowing. In growing
children, a notch can be seen in the femoral head, which represents the physis.
The femoral neck is the curvilinear hyperechoic structure extending distally from
the femoral head. Superficial to the femoral neck, the muscle fibers of the
iliopsoas muscle can be seen running directly above the joint capsule (Fig. 131.13
A ). An effusion is identified by the presence of fluid deep to the iliopsoas muscle
(Fig. 131.13 B ).
Technique
The patient should be positioned supine with the legs extended and the hips in
neutral position to allow for pooling of any joint fluid. A linear, high-frequency
probe is positioned parallel to the femoral neck in the sagittal plane. The probe
marker should be pointing to the patient’s umbilicus (Fig. 131.14 ).
An effusion is identified by the presence of an anechoic fluid collection deep to
the iliopsoas muscle in the synovial space, bordered by the synovial capsule (Fig.
131.13 ). Once the capsule is identified, the distance between the anterior surface
of the femoral neck and the posterior surface of the iliopsoas muscle is measured
for each hip. A measurement of greater than or equal to 5 mm or a difference of
greater than 2 mm from the contralateral hip is considered positive for an
effusion.
FIGURE 131.13 A: Normal hip. B: Hip effusion (arrow ).
Pitfalls
It is important to obtain images of both hips because comparison views of the
unaffected side can be helpful in identifying true pathology versus an anatomical
variant.
As with all musculoskeletal ultrasound, it is important that the probe be held
perpendicular to the skin and as parallel to the femoral neck as possible; a slightly
oblique angle may cause the synovial space to appear falsely hypoechoic (an
artifact known as anisotropy). Finally, these authors have found that the accepted
criteria for the diagnosis of hip effusion may be misleading in some patients. A
patient with small bilateral effusions (less than 5 mm) may not meet official
criteria by measurements, but if the joint space appears convex with anechoic
fluid within it, an effusion is likely present.
FIGURE 131.14 Probe position for hip ultrasound.
GENITOURINARY ULTRASOUND
First Trimester Ultrasound
Abdominal pain in the pregnant adolescent female is a common presenting
complaint. The differential diagnosis is broad, ranging from benign self-limited
conditions to a spectrum of life-threatening and organ-threatening conditions.
Ectopic pregnancy must be identified and treated rapidly. It is the leading cause of
maternal mortality in the United States and has a reported prevalence as high as
8% for a pregnant patient presenting to the ED.
Multiple studies have demonstrated the value of emergency bedside ultrasound
to evaluate first trimester pregnant patients with vaginal bleeding or abdominal
pain, specifically in ruling in those patients with a normal intrauterine pregnancy
(IUP) and thus, ruling out ectopic pregnancy. A pregnancy of only 5 to 6 weeks’
gestation can usually be seen. Not only is there excellent sensitivity and
specificity for identifying an IUP by bedside ultrasound, there is also reduction in
the time to definitive therapy in patients with an ectopic pregnancy, as well as
reduction in the length of stay in patients with IUPs.
The basic question that needs to be answered in first trimester ultrasound is: “Is
there an intrauterine pregnancy?” By virtue of visualizing an IUP, an ectopic
pregnancy is ruled out by exclusion, except in rare cases of multiple gestation
pregnancies with concomitant ectopic pregnancies and IUPs. In patients with
increased risk of heterotopic pregnancies, confirming an IUP does not obviate the
need to search for an ectopic pregnancy when there is clinical suspicion. This
subset of pregnant patients should always have a formal comprehensive
ultrasound done by the radiology or gynecology service.
Anatomy
The bladder lies anterior to the uterus. This relationship allows a full bladder to
be used as an acoustic window to visualize the uterus. An empty bladder renders
the transabdominal approach much more difficult. When the bladder is empty, the
uterus will often lie more anterior and superior and the transvaginal approach is
preferred to maximize visualization of the uterus.
Technique
Either a transabdominal or transvaginal technique can be used to assess for IUP.
A low-frequency curvilinear or phased array probe should be used for the
transabdominal approach. As detailed above, transabdominal sonography should
be performed through a distended urinary bladder. This may not be practical in a
busy ED. The probe should be positioned longitudinally just above the pubic
symphysis and directed through the bladder to visualize a longitudinal view of the
uterus, cervix, and pouch of Douglas with cephalad structures on the left side of
the monitor (Fig. 131.15 ). In the nonpregnant female, the endometrial stripe may
be visualized without any uterine contents. The ovaries can often be visualized by
sliding the probe laterally and directing the beam toward the opposite side;
compression of the abdominal wall externally may also aid with visualization.
Transverse images should also be obtained and may allow for visualization of the
uterus and adjacent adnexa in the same image.
