Diagnostic Ultrasound - Abdomen and Pelvis

Approach to Splenic Sonography
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Diagnoses: Spleen
Transducer Selection
Similar to other intraabdominal organs, the spleen is best
imaged using a 3-5 MHz curvilinear transducer. A curvilinear
(or curved) transducer is preferred due to its larger area of
coverage (suitable to include the entire span of the spleen), as
compared to a sector (vector) transducer or linear array
transducer.
Finding an Acoustic Window
The spleen is an intraperitoneal organ of variable size and
morphology that occupies the left upper quadrant. The
anatomy of the spleen and its relationships to adjacent organs
are discussed in a separate chapter. Visualization of the spleen
in the left upper quadrant is challenged by several anatomic
factors, chiefly artifacts caused by the ribs, the left lung, the
splenic flexure of the colon, and the stomach. The positioning
of both the transducer and the patient will play a role in
optimizing the acoustic window.
An anterior subcostal approach may be attempted in the
supine position, though such an approach is often limited due
to bowel gas artifact from the colon &/or the stomach. When
this view can be successfully achieved, it will often require an
anterolateral oblique positioning of the transducer.
Occasionally, patients may have variant liver anatomy in which
the left hepatic lobe extends far across midline to the left
upper quadrant. In this setting, the left hepatic lobe may serve
as an acoustic window to visualize the spleen. A posterior
approach is of little utility, limited by the anatomy of the lungs
and diaphragm, which extend most caudally at this site.
A lateral or posterolateral intercostal approach, with
transducer parallel to the ribs and the patient in the supine or
right lateral decubitus (i.e., left-side up) position, provides the
best acoustic window for the spleen. The 10th to 11th rib
intercostal space is an ideal place to start. The 9th to 10th rib
intercostal space may also yield a satisfactory window.
Several other techniques may aid in visualization of the spleen.
Positioning the patient in the supine or right lateral decubitus
positions has already been discussed. Note, however, the right
lateral decubitus position may cause the spleen to fall away
from the chest and abdominal wall, reducing visualization of
the organ from an intercostal approach. Having the patient
fast prior to the ultrasound examination may reduce gaseous
distension of the stomach in the left upper quadrant. This may
not be possible in the emergency setting, but can be feasible
in the outpatient setting. During the ultrasound examination,
asking the patient to perform deep inspiration (to bring the
spleen down into the field of view) is a useful technique.
Experimenting with different degrees of inspiration or
expiration (partial or complete) with breath hold may improve
visualization.
Anatomic Orientation and Imaging Planes
The posterolateral intercostal approach is the favored acoustic
window of most sonographers and radiologists. Because of
the orientation of the ribs, an intercostal approach effectively
provides an oblique plane with respect to the standard x, y,
and z anatomical planes of the body (i.e., the axial, coronal,
and sagittal planes). Fortunately, because the anatomic
orientation of the spleen is variable and may itself lie obliquely
compared to the standard anatomical planes, this
posterolateral oblique view is well-suited to identify the long
axis of the spleen. By standard convention, this anatomically
oblique plane is referred to as the "longitudinal" plane of the
spleen (often abbreviated "long"). When the transducer
orientation is flipped by 180°, this is, by convention, referred
to as the "transverse" plane of the spleen (often abbreviated
"trans").
Note that the conventional "longitudinal" and "transverse"
planes of the spleen via the posterolateral intercostal
approach are not perpendicular views; rather, they are mirror
images of each other. The true transverse cross section of the
spleen would be pie- or oval-shaped, rather than crescentshaped
(as is seen in the longitudinal cross section). A true
transverse image of the spleen could be obtained either by a
90° rotation of the transducer in the intercostal approach (a
view that is limited by the orientation of the ribs) or from an
oblique anterior subcostal approach (which is often limited by
bowel gas artifact).
Because of both the transducer orientation and the spleen's
anatomic orientation, the conventional "longitudinal spleen"
view (truly a longitudinal oblique) does not correspond
directly to the traditional coronal or sagittal planes of CT or
MR. Likewise, the conventional "transverse spleen" view does
not correspond directly to the axial plane of CT or MR. In a
similar regard, the "longitudinal spleen" view and the
"longitudinal left kidney" view will not represent the same
anatomic plane in the same patient, as these planes are
"longitudinal" to the organs of interest, not the patient's body.
Understanding the difference between imaging planes and
anatomic planes also has important implications for the
measurement of spleen size. By convention, the splenic length
is measured as the greatest dimension in the "longitudinal"
view. Splenic thickness is measured from the hilum to outer
capsule on the "transverse" view (though it would be the same
measurement on the "longitudinal" view). Splenic width is
generally considered the greatest dimension on the
"transverse" view, but because of the discrepancies in imaging
and anatomic planes, the sonographic splenic width based on
the conventional transverse view and the true splenic width
(most accurately measured by CT or MR) are not synonymous.
The maximum splenic dimension on the conventional
longitudinal and transverse views are, in actuality, the same
measurement.
Routine Evaluation of Spleen
The standard evaluation of the spleen involves both grayscale
and color Doppler interrogation. On grayscale ultrasound, the
size, echotexture, and overall morphology of the spleen
should be documented. As previously described, the size may
be documented in terms of the length and thickness (and less
accurately, the width, as described previously). The presence
or absence of perisplenic fluid should also be noted.
Routine evaluation of the splenic vein is an important
component of a thorough sonographic exam of the spleen.
The splenic vein can be assessed in two locations: at the
splenic hilum and at midline, posterior to the pancreas. Proper
interrogation of the splenic vein involves evaluating for vessel
patency and ensuring flow is appropriately directed away
from the spleen, toward the liver (hepatopetal flow). Splenic
vein flow may be reversed, for example, in the setting of
chronic portal hypertension.
The splenic artery is often not part of routine splenic
evaluation, but should be included when assessing for causes
of splenic infarction or other vascular abnormalities of the
spleen. Like the vein, the splenic artery can be assessed at the