Myelolipoma of the Adrenal Gland

Author(s)
Eranga Perera, Shweta Bhatt,MD, Vikram S Dogra,MD.
Research assistant
University of Rochester.
Images
  • Figure 1 myelo new.jpg
  • Figure 2 myelo new.jpg
  • Figure 3 myelo new.jpg
  • Figure 4 myelo new.jpg

Figure Legends : 

Figure 1 and 2: Axial and reformatted coronal images of a plain CT scan abdomen shows a fat density lesion involving the right adrenal gland ,  3.8x 4.0x5.2 cm in size (arrow).

Figure 3 and 4: PET scan performed to evaluate the known malignancy in the patient does not demonstrate any tracer uptake by  the adrenal lesion(arrow).

Case Description

Clinical History: 

Eighty year old patient diagnosed with  Mantle Cell Lymphoma, Computed Tomography and PET scan done for evaluation and staging.

Diagnosis: 

Adrenal gland Myelolipoma.

Discussion: 

Fat containing tumors of the adrenal gland are uncommon. It is described with an incidence of 0.08 to 0.2% at autopsy [1]. They comprise of myelolipoma, angiomyolipoma, teratoma, lipoma and liposarcoma. They usually present as an incidental finding in asymptomatic individuals or present with non specific symptoms.

Myelolipoma;

Myelolipoma is a rare, benign nonfunctioning tumor composed of mature adipose tissue and hematopoietic tissue and it is the commonest fat containing tumor of adrenal gland [2]. It arises from the zona fasciculata of the adrenal cortex and has an equal sex frequency. It affects both glands equally and the tumor size can be variable, but is usually less than 5 cm in diameter at the time of presentation [1,2]. Myelolipoma usually presents in the fifth or sixth decade as an asymptomatic, incidental finding. They may present with symptoms if the tumor undergoes hemorrhage, necrosis or if it compresses the surrounding structures when it enlarges in size [1, 2]. Imaging findings of the myelolipoma depends on the proportion of fat, myeloid tissue, hemorrhage and calcification.

Lipoma

Adrenal lipomas are uncommon compared to myelolipoma [2]. The pathogenesis of adrenal lipoma is unknown although adrenal lipoma and myelolipoma are believed to be of same tumor origin. They comprise 0.02% of the primary adrenal tumors. The size of an adrenal lipoma can vary from 1.5cm to 12cm. Surgery is recommended for larger tumors due to the potential risk of malignancy and to relieve the symptoms [2].

Angiomyolipoma:

Angiomyolipoma is a rare mesenchymal tumor usually found in the kidney. Extrarenal angiomyolipoma is most commonly found in the liver. Las et al reported two cases of adrenal angiomyolipoma in their study of adrenal lipomatous tumors in twenty patients [2].

Liposarcoma:

 Retroperitoneum and the lower extremities are the two commonest sites where a liposarcoma can occur. They usually present as large tumors. Extensive cystic degeneration is an unusual feature of adrenal liposarcoma and it can simulate benign cystic lesion in imaging [2].Other differential considerations for an adrenal liposarcoma include adrenal carcinoma and adrenal cysts.

Teratoma:

Adrenal teratoma consists of mature tissue arising from more than one germinal layer. They contain large amount of fatty tissue as well as calcification and bone [2].

 

Role of imaging:

On gray scale sonography, the fatty lesions of adrenal gland appear as an echogenic mass in adrenal bed, which can be homogenous or heterogeneous in echotexture. It may be difficult to differentiate a mass from the retroperitoneal fat when the tumor is small. Presence of propagation speed artifact helps in identification of the mass [1]. The “propagation speed artifact” is described as the diaphragmatic disruption due to decreased velocity of sound when propagating through fatty tissue which was first described by Richman et al [1,3]But this artifact is reported when the mass is more than 4cm in diameter, and does not help in differentiating a myelolipoma from lipoma or liposarcoma [1,4]. If the tumor consists predominantly of myeloid tissue it may appear hypoechoic.

Computed Tomography is considered the modality of choice in the  identification of adrenal gland pathology. CT has a higher sensitivity in identifying the adrenal gland compared to MRI due to its better spatial resolution [5]. Demonstration of macroscopic fat in adrenal gland is sufficient to make the diagnosis of myelolipoma. Occasionally some lesions may not contain sufficient fat to demonstrate on unenhanced CT [4].

 MRI scan gives a better contrast resolution between the adrenal gland and the adjacent organs. On spin echo T1W images the myelolipoma appear as a high signal intensity lesion and has intermediate signal intensity on T2W sequences. Due to the presence of bone marrow component they often appear heterogeneously hyperintense on T2W sequences [6]. Chemical shift artifact can be used to confirm the microscopic fat within a lesion. The inherent difference in precessional frequency of fat and water cases misregistration, artifact which is used for diagnosing a fat containing lesions as chemical shift imaging [7].

References / Suggested Reading: 

1: Rumack CM. Wilson SR. Charboneau W. Johnson JA. MD. Diagnostic ultrasound, third edition.

2: Lam KY, Lo CY. Adrenal Lipomatous Tumors: A thirty year old Clinicopathological experience at a single institution.J Clin Pathol 2001 :54; 707-712.

3: Richman TS, Taylor KJW, Kremkau FW. Propagation speed artifact in a fatty tumor(myelolipoma) : Significant for tissue differential diagnosis. J Ultrasound Med 1983;2:45-47.

4: Dunnik NR. Adrenal Imaging: Current status. AJR 1990 May; 154: 927-936.

5:Schults CL. Haaga JR. Fletcher BD et al. Magnetic Resonance Imaging of the Adrenal Glands. A comparison with computed tomography.AJR 1984 December ;143: 1235-1240.

6:Krebs TL. Wagner BJ. MR Imaging of the Adrenal Gland: Radiologic-Pathologic correlation. RadioGraphics 1998; 18: 1425-1440

7: Hood MN, Ho VB. Smirniotopoulos. Szumowski J. Che

Citation:

Myelolipoma of the Adrenal Gland, Eranga Perera, Shweta Bhatt,MD, Vikram S Dogra,MD., Imaging Science Today, 2010, 2229.