Diagnostic Ultrasound - Abdomen and Pelvis

Myelolipoma
Diagnoses: Adrenal Gland
○ When large may appear heterogeneous due to areas of
necrosis and hemorrhage
○ Multiplanar CT or MR best characterizes origin from
adjacent kidney
• Liposarcoma
○ Retroperitoneal primary sarcoma in perirenal space
○ Displaces or invades adrenal gland as opposed to arising
from it
• Retroperitoneal teratoma
○ Uncommon neoplasm composed of mixed dermal
elements derived from 3 germ cell layers
○ Fat-fluid (sebum) level and chemical shift between fat
and fluid are pathognomonic
Adrenal Adenoma
• Well-defined, small, solid, round, hypoechoic adrenal mass
• Lipid-rich adenoma shows greater signal loss on chemical
shift MR, while myelolipoma shows greater signal loss with
fat saturated sequences
Adrenal Metastases/Lymphoma
• Metastases: Usually < 5 cm, variable appearance, may be
hypervascular on color Doppler
○ Usually known to have primary malignancy elsewhere
• Lymphoma:Discrete or diffuse mass, adrenal shape
maintained
○ Often bilateral with retroperitoneal masses or
retroperitoneal tumor engulfing adrenal
Adrenal Carcinoma
• Rare, unilateral, solid mass with heterogeneous
echogenicity
• Exceedingly rare cases may contain macroscopic fat
• Areas of necrosis and hemorrhage ± calcification (> 30%)
PATHOLOGY
General Features
• Etiology
○ Best hypothesis: Metaplasia of adrenal cortical cells
resulting from chronic stress or degeneration
○ Secondary hypothesis: Myelolipoma represents site of
extramedullary hematopoiesis
• Associated abnormalities
○ Adrenal collision tumors: Independently coexisting
neoplasms without significant tissue admixture (e.g.,
adrenal adenoma and myelolipoma)
○ Endocrine disorders in 7%; Cushing syndrome,
congenital adrenal hyperplasia (21-hydroxylase
deficiency), and Conn syndrome
○ Nonhyperfunctioning adenoma 15%
Gross Pathologic & Surgical Features
• Mass with pseudocapsule; contains fat and soft tissue
components
Microscopic Features
• Mature fat cells with variable mixture of myeloid cells,
erythroid cells, megakaryocytes, and occasional
lymphocytes; no malignant cells
CLINICAL ISSUES
Presentation
• Most common signs/symptoms
○ Usually asymptomatic and incidental finding on CT, MR,
or US (9% of adrenal incidentalomas)
○ Acute abdomen: Rupture with hemorrhage (rare)
• Other signs/symptoms
○ Pain from necrosis, hemorrhage, or compression of
structures
Demographics
• Age
○ Usually in older age group: 50-70 years
○ Uncommon in patients younger than 30 years
• Gender
○ Occur with equal frequency in men and women
• Epidemiology
○ Autopsy incidence: 0.2-0.4%
Natural History & Prognosis
• Complication: Rupture with hemorrhage usually when > 4
cm
• Prognosis: Excellent
• No malignant transformation
Treatment
• When diagnosis is certain and patient is asymptomatic,
surgery is not necessary
• If symptomatic, enlarging, or > 7 cm, surgery indicated due
to increased risk of bleeding and rupture
DIAGNOSTIC CHECKLIST
Consider
• Differentiate from other fat-containing tumors, most
importantly retroperitoneal liposarcoma
Image Interpretation Pearls
• Well-marginated fat-containing adrenal mass is virtually
diagnostic
• Diagnosis: CT or MR; biopsy prone to sampling error
• Presence of tumoral fat confirms diagnosis of this benign
lesion, obviating need for further work-up
SELECTED REFERENCES
1. Katabathina VS et al: Adrenal collision tumors and their mimics:
multimodality imaging findings. Cancer Imaging. 13(4):602-10, 2013
2. Aron D et al: Adrenal incidentalomas. Best Pract Res Clin Endocrinol Metab.
26(1):69-82, 2012
3. Song JH et al: The incidental adrenal mass on CT: Prevalence of adrenal
disease in 1049 consecutive adrenal masses in patients with no known
malignancy. AJR 190: 1163-1168; 2008
4. Daneshmand S et al: Adrenal myelolipoma: diagnosis and management. Urol
J. 3(2):71-4, 2006
590