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title: "Adrenal Myelolipoma"
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docid: "5813a554-06a4-4696-af71-7ce50693039d"
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breadcrumbs:
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- "Genitourinary"
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- "Diagnosis"
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- "Adrenal"
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- "Benign Neoplasms"
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- "Adrenal Myelolipoma"
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---
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# KEY FACTS
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- ## Terminology
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- Uncommon benign tumor composed of mature fat tissue and hematopoietic elements (myeloid and erythroid cells)
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- ## Imaging
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- Benign, nonfunctioning adrenal tumor
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- Accounts for 7-15% of incidental adrenal masses, usually in older population
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- Typically unilateral and very rarely bilateral
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- Large tumors can mimic retroperitoneal lipomas, liposarcomas
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- Asymptomatic, though larger tumors may hemorrhage
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- CT
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- Lesion containing fat attenuation (-30 to -90 HU)
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- Usually well-defined mass with recognizable pseudocapsule (remaining adrenal)
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- Punctate calcifications seen in 24% of cases
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- Coronal reconstruction helpful to differentiate from exophytic renal angiomyolipoma
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- MR
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- Tumor with major fat component
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- T1WI in phase: Typically hyperintense
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- FS sequences: Loss of signal
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- ## Top Differential Diagnoses
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- Adrenal adenoma
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- Intracellular lipid vs. macroscopic fat
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- Adrenal metastases and lymphoma
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- Retroperitoneal liposarcoma
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- Involving perirenal space, may simulate adrenal (or renal) fatty tumor
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- Pheochromocytoma
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- Highly vascular, prone to hemorrhage and necrosis
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- Adrenal carcinoma
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- Renal angiomyelolipoma
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- Coronal CT reconstruction or MR useful to determine organ of origin
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# TERMINOLOGY
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- ## Definitions
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- Uncommon benign tumor composed of mature adipose tissue and hematopoietic elements
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# IMAGING
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- ## General Features
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- ### Best diagnostic clue
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- Suprarenal mass containing fat
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- ### Location
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- Suprarenal
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- Rare extraadrenal myelolipomas (presacral, retroperitoneal)
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- ### Size
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- Usually 2-10 cm, rarely 10-20 cm
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- Key concepts
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- Benign neoplasm of adrenal gland
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- Autopsy prevalence rate of 0.2-0.4%
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- Accounts for 7-15% of adrenal "incidentalomas"
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- Usually unilateral incidental finding in older patient
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- Larger tumors can bleed spontaneously
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- Most are nonfunctioning (do not secrete hormones)
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- Large myelolipomas can mimic retroperitoneal lipoma or liposarcoma
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- ## CT Findings
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- CT appearance depends on histologic composition
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- Most tumors are heterogeneous adrenal masses composed of varying percentages of fat
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- Low-attenuation suprarenal lesion containing fat density (-30 to -90 HU)
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- Average NECT attenuation value of tumor: -74 HU in one series
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- Interspersed soft tissue attenuation components: Myeloid elements, hemorrhage
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- Presence of macroscopic fat within tumor is diagnostic
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- Punctate calcifications seen in 24% of cases
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- Usually well-defined mass with recognizable pseudocapsule (remnant adrenal)
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- Coronal reconstructions may help determine organ of origin: Adrenal myelolipoma vs. exophytic renal angiomyelolipoma
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- ## MR Findings
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- MR appearance depends on histologic composition
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- Tumor with major fat component
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- T1WI in phase: Typically hyperintense
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- T1WI out phase: Persistent hyperintensity of macroscopic fat
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- T1WI FS: Confirmatory suppression of signal
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- Bone marrow elements (myeloid and erythroid cells)
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- Low signal on T1WI, moderate signal on T2WI
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- Hemorrhage: Varying T1, T2 signal depending on age of blood
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- ## Ultrasonographic Findings
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- ### Grayscale ultrasound
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- Well-defined, echogenic mass (↑ fat tissue)
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- Often overlooked: Lack of mass effect and isoechogenicity relative to retroperitoneal fat
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- Heterogeneous mass (↑ myeloid cells)
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- ## Angiographic Findings
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- Conventional
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- Differentiate myelolipoma from retroperitoneal liposarcoma by determining origin of blood supply and vascularity of tumors
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- ## Nuclear Medicine Findings
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- Typically not metabolically active, though uptake reported at FDG PET
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- ## Imaging Recommendations
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- Helical NECT or MR with FS sequence
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# DIFFERENTIAL DIAGNOSIS
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- [Adrenal Adenoma](/document/adrenal-adenoma/e2916d86-5f9f-4dd3-9576-1a7b89d8dda0)
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- Lipid-rich adenoma: ↓ attenuation (< 10 HU) at NECT
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- Can contain small amounts of macroscopic fat due to lipomatous metaplasia
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- CECT: Washout 15 minutes post injection: > 50%
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- Relative washout: > 40%
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- Absolute washout: > 60%
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- [Metastases and Lymphoma, Adrenal](/document/adrenal-lymphoma/44639c90-bd04-4e2a-a470-2c28a0e2ff78)
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- Bilateral lesions: Clinical history paramount
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- Metastases: Soft tissue attenuation (signal)
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- Lymphoma: May maintain adreniform shape, adjacent retroperitoneal adenopathy
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- [Liposarcoma, Retroperitoneal](/document/retroperitoneal-sarcoma/c1466b30-b730-41c4-a065-2c2de018a5f7)
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- Retroperitoneal primary sarcoma involving perirenal space may simulate adrenal (or renal) fatty tumor
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- [Pheochromocytoma](/document/pheochromocytoma/7d3c4062-643c-4030-8783-f85184ad8132)
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- Highly vascular, prone to hemorrhage and necrosis
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- Hyperintense on T2WI, bilateral in multiple endocrine neoplasia syndromes (MEN) syndromes
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- Clinical history (labile hypertension) and urinary catecholamines
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- [Adrenal Carcinoma](/document/adrenal-cortical-carcinoma/bdc7a08b-a64f-4bd2-9dfc-24331728e85e)
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- Rare, unilateral, invasive, enhancing mass
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- Venous invasion, distant metastases
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- May contain fat: Engulfed retroperitoneal fat vs. lipomatous metaplasia
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- ## Renal Angiomyelolipoma
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- Exophytic upper pole angiomyolipoma may mimic
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- Coronal reconstruction/MR helpful to determine organ of origin
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# PATHOLOGY
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- ## General Features
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- ### Etiology
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- Unknown
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- Best hypothesis: Reticuloendothelial cell metaplasia of capillaries in adrenal (stress/infection/necrosis)
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- Secondary hypothesis: Myelolipoma represents site of extramedullary hematopoiesis
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- ### Associated abnormalities
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- Adrenal collision tumors (coexistent myelolipoma and adenoma typical)
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- Large, bilateral myelolipomas reported with longstanding, poorly treated congenital adrenal hyperplasia
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- ## Gross Pathologic & Surgical Features
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- Cut section: Fat, soft tissue components
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- ## Microscopic Features
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- Mature fat cells and megakaryocytes; no malignant cells
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- Calcification
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- Hemorrhage within larger lesions
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# CLINICAL ISSUES
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- ## Presentation
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- ### Most common signs/symptoms
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- Asymptomatic
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- Usually incidental finding on CT, MR
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- Typically biochemically nonfunctioning
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- Symptomatic
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- Acute abdomen: Flank pain due to rupture and hemorrhage
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- Case reports of hormonally active tumors: Cushing, Conn syndromes, virilization
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- Diagnosis: Pathognomonic MR/CT features
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- Biopsy reserved for larger, atypical lesions, though prone to sampling error
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- ## Demographics
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- ### Age
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- Usually older patients (50-70 years old)
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- ### Epidemiology
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- Autopsy incidence: 0.2-0.4%
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- ## Natural History & Prognosis
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- Complication: Rupture with hemorrhage (rare)
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- Prognosis: Excellent
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- ## Treatment
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- When diagnosis is certain, surgery not needed for lesions < 5-7 cm
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- Surgery reserved for larger, symptomatic, or atypical lesions
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- Surgical series have confirmed utility of laparoscopic resection
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# DIAGNOSTIC CHECKLIST
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- ## Consider
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- Differentiate from other tumors (lipid-rich adenoma)
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- Key is presence of imaging-apparent adipose tissue; avoid further work-up for incidental mass
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- ## Image Interpretation Pearls
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- Well-defined, heterogeneous, fat-attenuation tumor on CT
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- T1 hyperintense, signal loss with fat suppression
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