Diagnostic ultrasound ( PDFDrive )

CHAPTER 4 The Liver 91
FIG. 4.25 Pneumocystis carinii. Disseminated P. carinii infection
in patient with AIDS who previously used pentamidine inhaler. Sonogram
shows innumerable tiny, bright echogenic foci without shadowing
throughout the liver parenchyma.
Pneumocystis carinii
Pneumocystis carinii is the most common organism causing
opportunistic infection in patients with acquired immunodeiciency
syndrome (AIDS). Pneumocystis pneumonia is the most
common cause of life-threatening infection in patients with
human immunodeiciency virus (HIV). P. carinii also afects
patients undergoing bone marrow and organ transplantation,
as well as those receiving corticosteroids or chemotherapy. 48
Extrapulmonary P. carinii infection was being reported with
frequency in the early 1990s. 49-52 It was postulated that the use
of maintenance aerosolized pentamidine achieved lower systemic
levels than the intravenous form, allowing subclinical pulmonary
infections and systemic dissemination of the protozoa. his
treatment is now infrequently used by AIDS patients, so disseminated
infection is rarely seen. Extrapulmonary P. carinii
infection has been documented in the liver, spleen, renal cortex,
thyroid gland, pancreas, and lymph nodes.
he sonographic indings of P. carinii involvement of
the liver range from tiny, difuse, nonshadowing echogenic
foci to extensive replacement of the normal hepatic parenchyma
by echogenic clumps representing dense calciication
(Fig. 4.25). A similar sonographic pattern has been identiied with
hepatic infection by Mycobacterium avium-intracellulare and
cytomegalovirus. 53
DISORDERS OF METABOLISM
Fatty Liver
Fatty liver is an acquired, reversible disorder of metabolism,
resulting in an accumulation of triglycerides within the hepatocytes.
he most common cause likely is obesity. Fatty liver
is recognized as a signiicant component of the metabolic
syndrome, the importance of which is being increasingly
recognized. Excessive alcohol intake produces a fatty liver by
stimulating lipolysis, as does starvation. Other causes of fatty
iniltration include poorly controlled hyperlipidemia, diabetes,
excess exogenous or endogenous corticosteroids, pregnancy, total
parenteral hyperalimentation, severe hepatitis, glycogen storage
disease, jejunoileal bypass procedures for obesity, cystic ibrosis,
congenital generalized lipodystrophy, several chemotherapeutic
agents (including methotrexate), and toxins such as carbon
tetrachloride and yellow phosphorus. Correction of the primary
abnormality will usually reverse the process, although it is now
recognized that fatty iniltration of the liver is the precursor for
signiicant chronic disease and HCC in some patients. Fatty liver
is attributed with the increasing incidence of HCC now seen in
Western countries.
Sonography of fatty iniltration varies depending on the
amount of fat and whether deposits are difuse or focal 54
(Fig. 4.26). Difuse steatosis may appear as follows:
• Mild—Minimal difuse increase in hepatic echogenicity with
normal visualization of diaphragm and intrahepatic vessel
borders
• Moderate—Moderate difuse increase in hepatic echogenicity
with slightly impaired visualization of intrahepatic vessels
and diaphragm
• Severe—Marked increase in echogenicity with poor penetration
of posterior segment of right lobe of liver and poor or no
visualization of hepatic vessels and diaphragm
Focal fatty iniltration and focal fatty sparing may mimic
neoplastic involvement. 55 In focal fatty iniltration, regions of
increased echogenicity are present within a background of normal
liver parenchyma (Video 4.3). Conversely, islands of normal liver
parenchyma may appear as hypoechoic masses within a dense,
fatty iniltrated liver (Video 4.4). Features of focal fatty change
include the following (Fig. 4.27):
• Focal fatty sparing and focal fatty liver most oten involve
the periportal region of the medial segment of the let lobe
(segment IV). 56,57
• Sparing also frequently occurs by the gallbladder fossa and
along the liver margins.
• Focal subcapsular fat may occur in diabetic patients receiving
insulin in peritoneal dialysate 58 (Fig. 4.27H and I).
• Lack of mass efect; hepatic vessels generally are not displaced,
although traversing vessels in metastases have been reported. 59
• Geometric margins are present, although focal fat may appear
round, nodular, or interdigitated with normal tissue. 60
• Rapid change with time; fatty iniltration may resolve as early
as 6 days.
Contrast-enhanced ultrasound (CEUS) is valuable in the
diferentiation of fatty change from neoplasia, because all of the
fatty or spared regions will appear isovascular in both the arterial
and the portal venous phase of enhancement. CT and magnetic
resonance imaging (MRI) can be used in distinguishing difuse
from focal fatty iniltration and in assessing for focal lesions.
Radionuclide liver and spleen scintigraphic examination will
yield normal results, indicating adequate numbers of Kupfer
cells within the fatty regions. 54 Some postulate that these focal
spared areas are caused by a regional decrease in portal blood
low, as demonstrated by CT scans during arterial portographic
examinations. 61 Knowledge of typical patterns and use of CT,