Pediatric emergency medicine trisk 1126
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FIGURE 131.15 Longitudinal view of uterus through the bladder. Arrows designate the
potential space of pouch of Douglas posterior to uterus.
An endocavitary probe should be used for the transvaginal approach. Although
the transvaginal transducer is of higher frequency and produces sharper images,
the field of view is more limited. The bladder should be emptied prior to
performing the scan. After the probe is cleaned and covered, it is inserted into the
vaginal canal with the marker facing anteriorly. It often helps to have the anxious
patient insert the probe into the vaginal canal herself. A standard transvaginal
longitudinal view is obtained (Fig. 131.16 ). Once the longitudinal view is
obtained, the probe should be rotated such that the marker is to the patient’s right
to obtain a transverse view. With each planar view, it is important to fan the probe
along the scanning plane axes to visualize the entire body of the uterus. More
experienced sonographers may also be able to visualize the fallopian tubes and
ovaries, but it is important to emphasize that the purpose of the examination is
primarily to determine the presence or absence of an IUP.
FIGURE 131.16 Standard transvaginal view of uterus.
In normal pregnancy, the earliest sonographic finding of an IUP is the
gestational sac, which appears as a round fluid collection within the uterus (
Video 131.15 ). In transabdominal scanning, the gestational sac can be seen as
early as 5 to 6 weeks’ gestational age. Transvaginal scanning can reliably detect
this finding about 7 to 10 days earlier. The yolk sac can be seen inside the
gestational sac at approximately 6 to 7 weeks’ gestational age (5 to 6 weeks by
transvaginal scanning) and most authors consider this as definitive evidence of
IUP. A normal embryo will appear at the margin of the yolk sac at about 6.5 to
7.5 weeks’ gestational age and cardiac activity can be detected shortly thereafter (
Video 131.16 ).
In the pregnant female, the standard for confirming an IUP on an emergency
physician performed bedside ultrasound requires visualization of an intrauterine
yolk sac, fetal pole, or intrauterine fetal heartbeat. Visualizing only the gestational
sac is not adequate as this can be the result of hormonal stimulation from an
ectopic pregnancy. When a fetal heartbeat can be seen, it should be documented
with M-mode.
In an ectopic pregnancy, an adnexal mass or free fluid in the pelvis can
sometimes be seen. However, visualization of the ectopic pregnancy should not
be the goal of the emergency physician. Several protocols have been developed
addressing the use of bedside pelvic sonography in the pregnant female. In
general, if an IUP is not seen in a patient with a positive urine B-HCG,
gynecology consultation should be arranged. A low-serum HCG level, implying
an early IUP, may allow outpatient follow-up with precautions for possible
ectopic pregnancy.
Pitfalls
A pregnancy less than 5 weeks’ gestational age (3 weeks post conception) may
not be visible. The gestational sac should be located off-center and should have a
circular appearance; elliptically shaped, centrally located sacs are concerning for
an abnormal sac that may not be representative of an IUP.
Kidney Ultrasound
Kidney ultrasound provides important diagnostic information in patients
presenting with hematuria and/or abdominal pain. Nephrolithiasis is an
increasingly recognized cause of pediatric abdominal pain and bedside ultrasound
offers the ability to quickly determine a diagnosis in the patient presenting with
obstructive nephropathy.
Early obstruction may initially only result in hydroureter but as the obstruction
persists, hydronephrosis will develop. Identification of hydronephrosis in a
patient with undifferentiated abdominal pain can help to focus further treatments
for presumed nephrolithiasis and often precludes the need for additional
diagnostic tests. While nephrolithiasis is the most common cause of acute
obstructive nephropathy, the possibility of extrinsic compression should also be
considered.
Ultrasound has become the first-line imaging modality in cases of suspected
renal colic. The pediatric literature is limited to case reports regarding the use of
bedside ultrasound for evaluation of renal pathology. In contrast, adult literature
has shown that bedside ultrasound is sensitive and specific for identification of
hydronephrosis secondary to obstructive uropathy in patients with renal colic.
Anatomy
Bilateral kidneys are located in the retroperitoneum, with the left kidney located
slightly more cephalad than the right. The kidneys are obliquely oriented with the
upper pole oriented medially and posteriorly. The kidney, along with the adrenal
gland, is surrounded by Gerota fascia, a hyperechoic linear structure. The outer
layer of the kidney comprises the renal cortex, a hypoechoic homogeneous tissue
with anechoic-appearing medullary pyramids interspersed. In the central kidney
the calyces, which appear hyperechoic due to the fat in the area, converge to form
the renal pelvis. In the inferior central kidney, the central hilum houses the entry
site of the ureter, renal vein, and renal artery (Fig. 131.17 ).
FIGURE 131.17 Normal kidney. Note that on the right side, the liver may be used as an
acoustic window.
Technique
The same approach used to perform the FAST should be used to perform a
focused image of the kidney. A low-frequency abdominal probe will allow for
best imaging and, in pediatric patients, a probe with a small footprint is often
preferable given the position of the kidneys within the thoracic ribcage. The
patient can be in the supine or decubitus position. The probe marker should be
positioned toward the head for the long-axis image and then rotated 90 degrees to
perform the short-axis image.
Obstructive ureteronephrolithiasis may initially cause dilation of the ureter,
which can be noted at the level of the central hilum. With worsening obstruction
and progression to hydronephrosis, the calyces and renal pelvis will dilate and the
central region of the kidney will become anechoic (
Video 131.17 ).
Identification of an obstructive stone is often difficult but, when noted, may
appear hyperechoic and cause shadowing (Fig. 131.18 ).
