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Renal Angiomyolipoma (AML)


KEY FACTS

Terminology

  • Benign renal tumor composed of abnormal blood vessels, smooth muscle, and adipose components

Imaging

  • Most common benign renal neoplasm

  • 80% are incidental findings on imaging

  • 90% are unilateral and solitary: Usually not associated with tuberous sclerosis (TSC)

  • 10% are multiple and bilateral: Usually due to TSC

    • 80% of TSC patients have renal angiomyolipomas (AMLs)

  • Solid, heterogeneous, renal cortical mass in adult with macroscopic fat is reliable sign of AML

    • Variable amounts of fat may be present

    • ~ 5% of AMLs contain minimal fat and cannot be reliably diagnosed by imaging

  • Lipid-poor AMLs are often hyperdense on NECT

Top Differential Diagnoses

  • Renal cell carcinoma (RCC)

    • Rarely reported to contain fat (engulfed sinus or perirenal fat)

    • Calcification/ossification within tumor is highly suggestive of RCC

  • Perirenal liposarcoma

    • Smooth compression of kidney and extension beyond perirenal space favor liposarcoma

    • Renal parenchymal defect and enlarged vessels favor AML

  • Wilms tumor

    • If child has TSC, mass more likely to be AML

    • Otherwise suspect Wilms tumor

  • Other less common considerations: Metastases, lymphoma, oncocytoma, lipoma, teratoma

Clinical Issues

  • Most common complication: Hemorrhage

  • Small subgroup of AMLs can be angioinvasive, affect local lymph nodes, and rarely metastasize

Graphic shows a vascular renal mass
with prominent fatty and soft tissue components. Note the large "feeding" arteries. This hypervascularity predisposes these tumors to spontaneous hemorrhage.

Sagittal US shows an echogenic lesion
in the superior cortex of the left kidney due to an incidental angiomyolipoma. Color flow was not identified in the lesion.

Axial NECT in the same patient demonstrates a fat attenuation lesion
in the superior cortex of the left kidney, consistent with an incidental angiomyolipoma.

Axial T1 postcontrast MR with fat saturation reveals an angiomyolipoma
that extends into the perinephric space. A cortical defect (notch sign)
identifies the origin of the angiomyolipoma from the kidney. A large vessel
also extends into the neoplasm from the kidney.

TERMINOLOGY

Abbreviations

  • AML

Synonyms

  • Renal hamartoma or choristoma

Definitions

  • Benign renal neoplasm composed of abnormal blood vessels, smooth muscle, and adipose components

IMAGING

General Features

  • Best diagnostic clue

    • Solid, heterogeneous, renal cortical mass containing macroscopic fat in adult

  • Size

    • Variable: Few mm to > 25 cm

  • Other general features

    • Most common benign tumor of kidney

    • 80% are incidental findings on imaging

    • 90% are unilateral and single: Usually not associated with tuberous sclerosis complex (TSC)

    • 10% are multiple and bilateral: Usually due to TSC

    • 20% of patients with renal AML have TSC

    • 80% of TSC patients have renal AMLs

    • Tuberous sclerosis complex (Bourneville disease)

      • –

        Facial angiofibroma, ungual fibroma

      • –

        Retinal hamartoma

      • –

        Cortical tubers and subependymal nodules

      • –

        Multiple renal angiomyolipomas

      • –

        Lymphangioleiomyomatosis (LAM)

        • □

          Progressive cystic lung disease

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