Discussion: Myelolipoma

Hormonal Evaluation

• Some guideline state specifically that masses diagnosed as myelolipoma require no hormonal evaluation.[1,2] Others state that hormonal evaluation is required for all adrenal incidentalomas[3] without special exception for those thought to be myelolipoma. Given the low cost and risk of hormonal evaluation, and the fact that foci of myelolipomatous tissue with gross fat have been observed within adrenal adenomas or associated with congenital adrenal hyperplasia, we recommend hormonal evaluation for patients with adrenal lesions that are highly likely to be myelolipoma based on imaging, especially those with only small regions of fat attenuation on CT.

Imaging

• The presence of an area of visible fat attenuation within an adrenal lesion is universally considered to be 100% specific for benign pathology (almost always myelolipoma) within the guidelines.[1–4] Series also suggest that this finding is 100% sensitive.[5]

  • No guideline contains an extended discussion, and most do not cite specific data, for treating macroscopic fat as 100% specific for benign lesions; however we are not aware of a single reported case contradicting this claim.

  • The guidelines also do not provide strict definitions of “fat attenuation” or of how large such an area needs to be to be considered.

    • In one series, areas of myelolipoma considered by expert radiologists to be of “fat attenuation” ranged from -130 to -23 HU (mean -74 HU).[5] A cutoff of -30 HU has been proposed.[6]

    • In most cases of adrenal myelolipoma >50% of the lesion is fat attenuation, so the finding rarely ambiguous.[5] Defining a minimum amount of fat attenuating area that must be seen to make the diagnosis is therefore unlikely to be helpful.

• It is perhaps theoretically possible to see a small amount of fat within a malignant adrenal mass; however as stated above, no such case has ever been reported.

  • There are case series which include myelolipomas occurring within (or co-occurring with) other adrenal pathology, including those resulting from congenital metabolic abnormalities (e.g. congenital adrenal hyperplasia) and adrenal adenomas. In these cases, the amount of macroscopic fat is usually less than 10% of the total size of the lesion.[5]

  • We are not aware of any theoretical reason why myelolipoma could not similarly co-occur with a carcinoma, though 1) the rarity of these two entities would make this extremely uncommon, 2) the amount of fat visible on CT would almost certainly be minute relative to the total volume of the mass and 3) the fact that we cannot identify a single such case in the literature makes this theoretical possibility irrelevant from a guideline perspective.  

Treatment

Additional Work Up

• When hormonal evaluation and imaging are suggestive of myelolipoma, no additional workup is required prior to observation or excision. (No guideline states this explicitly, but we are not aware of any paper which recommends a further work up.)

Treatment

• Intervention for small, asymptomatic myelolipomas is universally not recommended.

• Due to a risk of spontaneous retroperitoneal hemorrhage, surgical excision of large myelolipomas has been advocated, with various groups proposing cutoffs of 7cm[6], 8cm[7], and 10cm[5]. There are approximately 24 total cases of retroperitoneal hemorrhage associated with myelolipoma in the literature, with the smallest myelolipoma associated with hemorrhage measuring 7cm in diameter.[8]  In one series the size of tumors presenting with hemorrhage ranged from 8.5cm – 18.0cm with a mean of 14.2cm.[5] The severity of clinical presentation in these cases is unclear, though we are not aware of a reported case of death and transfusion appears uncommon.  We recommend that the decision for surgical intervention should therefore be individualized based on patient desires, symptoms, risk of hemorrhage, and risks of intervention, although unfortunately there is little data and no published guidelines to guide this.

Follow Up

• The American College of Radiology White Paper specifically recommends no follow up imaging for definitively benign lesions. This specifically includes myelolipomas, however there is no specific discussion or rationale given.[4] Other guidelines are mostly silent on the need for further imaging.[1–3] In the largest reported series of follow up of myelolipoma, which consists of only 13 patients, only half increased in size at all. Follow up was too short and change in size too variable to make any meaningful statements about growth rates in those that did grow.[9] It therefore seems reasonable to perform some kind of imaging to establish a growth rate in individual patients whose myelolipomas seem like they may one day meet size criteria for intervention, however there is no data to guide particular recommendations for this.

• Recurrence of myelolipoma following resection has not been reported. Therefore, we recommend no dedicated follow up imaging, although no published guidelines have specifically addressed this.

Last update: 11/28/2021, Marshall Strother

 References

1.          Reaume MN, Graham GE, Tomiak E, et al: Canadian guideline on genetic screening for hereditary renal cell cancers. Can. Urol. Assoc. J. 2013; 7: 319.

2.          Zeiger MA, Thompson GB, Duh Q-Y, et al: American Association Of Clinical Endocrinologists And American Association Of Endocrine Surgeons Medical Guidelines For The Management Of Adrenal Incidentalomas. Endocr. Pract.  2009; 15: 1–20.

3.          Fassnacht M, Arlt W, Bancos I, et al: Management of adrenal incidentalomas: European Society of Endocrinology Clinical Practice Guideline in collaboration with the European Network for the Study of Adrenal Tumors. Eur. J. Endocrinol. 2016; 175: G1–G34.

4.          Mayo-Smith WW, Song JH, Boland GL, et al: Management of Incidental Adrenal Masses: A White Paper of the ACR Incidental Findings Committee. J. Am. Coll. Radiol. 2017; 14: 1038–1044.

5.          Kenney PJ, Wagner BJ, Rao P, et al: Myelolipoma: CT and pathologic features. Radiology 1998; 208: 87–95.

6.          Daneshmand S and Quek ML: Adrenal myelolipoma: diagnosis and management. Urol. J. 2006; 3: 71–4.

7.          Gershuni VM, Bittner JG, Moley JF, et al: Adrenal Myelolipoma: Operative Indications and Outcomes. J. Laparoendosc. Adv. Surg. Tech. A 2014; 24: 8.

8.          Shenoy VG, Thota A, Shankar R, et al: Adrenal myelolipoma: Controversies in its management. Indian J. Urol. 2015; 31: 94.

9.          Han M, Burnett AL, Fishman EK, et al: The natural history and treatment of adrenal myelolipoma. J. Urol. 1997; 157: 1213–6.