Diagnostic ultrasound ( PDFDrive )

420 PART II Abdominal and Pelvic Sonography
A
B
C
FIG. 11.6 Adrenal Myelolipoma. (A) Sagittal and
(B) transverse sonograms show a solid heterogeneously
echogenic right adrenal mass (arrow). There is apparent
diaphragmatic disruption (arrowheads) as a result of
misregistration artifact (also known as propagation speed
artifact) as the sound travels slower through the fatty
mass (1450 m/sec) than through the adjacent normal liver
(1540 m/sec). (C) Sagittal computed tomographic image
demonstrates the predominantly fatty mass with some
wisps of soft tissue, conirming the diagnosis of myelolipoma
(arrow).
Sonographic Features
Sonographic features for adenomas can be nonspeciic but commonly
appear as small homogeneously hypoechoic masses with
well-deined borders and no substantial demonstrable vascularity.
Nonfunctional adenomas are oten larger and can have heterogeneous
features such as cystic necrosis, hemorrhage, and
sometimes calciication that make them diicult to distinguish
from malignant lesions.
Myelolipomas
Myelolipomas are rare benign tumors classically containing
mature adipose and hematopoietic tissue, with an estimated
prevalence of 0.08% to 0.4%. 12 hey have been histologically
compared to angiomyolipomas of the kidneys and therefore
exhibit similar imaging characteristics, being well-deined and
difusely echogenic. heir etiology and pathogenesis are unknown,
although these lesions are thought to arise in the zona fasciculata
of the adrenal cortex. Men and women are equally afected, with
tumors most oten occurring in the ith or sixth decade of life.
Diferential considerations include other fat-containing masses
within the retroperitoneum (Fig. 11.6).
Fat-Containing Suprarenal Masses
Adrenal myelolipoma
Exophytic renal angiomyolipoma
Lipoma
Retroperitoneal liposarcoma
Retroperitoneal teratoma
Pheochromocytoma (rare)
Sonographic Features
Macroscopic fat within myelolipomas can be appreciated as
homogeneous, highly echogenic components with associated
acoustic shadowing. When small, they may be diicult to