Adrenal gland myelolipoma

An adrenal myelolipoma is a rare, completely non-cancerous (benign) tumor that grows on top of the kidney. It is made of a unique mix of two everyday tissues: mature fat and bone marrow-like cells. Even though it contains bone marrow cells, it does not produce blood cells or cause any blood disorders.

Adrenal myelolipomas are classified by size:

• Small (under 4 cm): these are the most common. They cause zero symptoms and are simply monitored over time with regular scans to ensure they stay stable.

• Large (over 6 to 10 cm): as they grow, they can press against nearby organs, causing a dull ache. They also carry a higher risk of bleeding inside the abdomen.

• Giant (over 10 cm): these are very rare. Because of their massive size, they cause noticeable abdominal pain and a much higher risk of bursting, meaning doctors usually recommend surgery to remove them safely.

Unlike other adrenal growths, which need blood tests to check for hormone leakage, a myelolipoma is chemically inactive. An MRI can usually identify its large, characteristic pockets of fat, allowing for a confident diagnosis without an invasive biopsy.

For the related adrenal condition adrenal adenoma, which arises from the same gland but has different tissue composition and hormonal implications, see our dedicated adrenal adenoma page.

Symptoms of adrenal gland myelolipomas

The majority of adrenal myelolipomas cause no symptoms and are discovered entirely incidentally on abdominal imaging. When symptoms occur they reflect tumour size and any complications:

• A dull aching discomfort or fullness in the flank or upper abdomen in large tumours from mass effect on adjacent structures

• Sudden severe flank or abdominal pain from spontaneous haemorrhage into or around the tumour. This is a rare but serious complication requiring urgent assessment

• Nausea and early satiety from gastric compression by very large tumours

• A palpable abdominal mass in giant myelolipomas

Importantly, adrenal myelolipomas do not produce excess hormones. They do not cause hypertension, low potassium, Cushing's features, or virilisation. The absence of hormonal symptoms in an adrenal mass with characteristic macroscopic fat on MRI strongly supports the diagnosis.

What causes adrenal gland myelolipomas?

The exact cause of myelolipoma development is not fully understood. Contributing factors include:

• Metaplastic transformation the most widely accepted theory proposes that adrenocortical cells or stromal cells undergo metaplastic transformation into haematopoietic and adipose tissue, possibly in response to chronic adrenal stimulation or stress.

• Chronic ACTH stimulation conditions causing sustained elevation of ACTH, including congenital adrenal hyperplasia and Cushing's disease, are associated with higher myelolipoma prevalence, supporting the metaplastic theory.

• Congenital adrenal hyperplasia (CAH) has a particularly strong association with adrenal myelolipoma, with bilateral and sometimes massive myelolipomas occurring in poorly controlled CAH from chronic ACTH-driven adrenal stimulation.

• Obesity and metabolic syndrome are associated with increased myelolipoma prevalence through mechanisms that are not fully understood.

• Age myelolipomas are predominantly a disease of middle-aged and older adults, with peak incidence in the fifth and sixth decades.

• Genetic factors occasional familial clustering suggests a genetic predisposition in some cases.

How is an adrenal gland myelolipoma detected?

Adrenal myelolipomas are detected through abdominal imaging, with blood tests assessing adrenal hormonal function and identifying any associated conditions.

Abdominal MRI While CT is traditionally the most sensitive tool for confirming the fat content that defines a myelolipoma, Elfcare’s full-body MRI can also reliably identify one, using fat-suppression imaging to pick up its characteristic large fat pockets, which usually allows it to be distinguished from more concerning adrenal masses without a biopsy. The MRI also tracks the tumour's size, checks for any internal bleeding, and maps its position relative to nearby organs, useful if it grows large enough to need surgical removal.

Blood tests cannot detect myelolipoma directly but assess adrenal hormonal function to confirm non-functioning status and identify any associated conditions. Relevant markers in Elfcare's panel include:

• Cortisol confirms the absence of autonomous cortisol secretion, distinguishing myelolipoma from a cortisol-secreting adenoma that may coexist with or mimic a myelolipoma

• Potassium normal potassium supports non-functioning status, as hypokalaemia would suggest a coexisting aldosterone-secreting lesion

• HbA1c and glucose metabolic health assessment relevant to the obesity and metabolic syndrome association with myelolipoma

• Full blood count haemoglobin and platelet count assess for haematological consequences of spontaneous haemorrhage from a large myelolipoma and provide baseline assessment

• CRP elevated CRP with flank pain raises concern for haemorrhage or infection associated with a large myelolipoma

• 17-hydroxyprogesterone the primary screening marker for congenital adrenal hyperplasia, the most important associated condition in bilateral or multiple myelolipomas.

• ACTH elevated in congenital adrenal hyperplasia and Cushing's disease, both associated with myelolipoma development. Arranged through specialist follow-up when indicated.

Why early detection matters

For the majority of people with a small adrenal myelolipoma, early detection provides a definitive diagnosis and clear reassurance that the finding requires only periodic monitoring rather than immediate intervention. This clarity has real value, replacing anxiety about an unexplained adrenal mass with a precise and reassuring clinical explanation. For larger myelolipomas, early identification allows for size monitoring and elective surgical planning before spontaneous haemorrhage occurs, which is a significantly safer scenario than emergency surgery for a ruptured myelolipoma. For those in whom bilateral myelolipomas prompt investigation for congenital adrenal hyperplasia, early identification of inadequately controlled CAH allows for treatment optimisation that prevents the ongoing ACTH-driven adrenal stimulation responsible for continued myelolipoma growth.

How Elfcare can help

Elfcare's full body MRI images both adrenal glands directly as part of the standard abdominal sequence, identifying the characteristic macroscopic fat signal of adrenal myelolipoma and providing a confident diagnosis in the vast majority of cases without the need for biopsy. For a finding that is almost always entirely benign, this imaging assessment provides both the diagnosis and the reassurance that distinguishes myelolipoma from more concerning adrenal masses.

Our blood panel covers cortisol, potassium, full blood count, HbA1c, and CRP, confirming the non-functioning status of the lesion and identifying any associated conditions or complications.

If our MRI or blood tests identify an adrenal myelolipoma or related adrenal finding, we take care of further diagnostics or refer you to the appropriate specialist.