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Extra-adrenal myelolipomas are extremely rare myelolipomas that occur outside the adrenal glands, with the most common sites being the retroperitoneum (especially presacral region 7), perirenal space and the thorax.
The exact incidence is unknown. Less than 60 reported cases were reported by 2014 3. There is a slight female predominance with an average age of detection at 50 to 70 years.
The majority of patients are asymptomatic at the time of diagnosis, and lesions are discovered incidentally on imaging for other medical problems. Symptomatic patients may complain of vague abdominal pain due to hemorrhage, mechanical compression, or tumor infarction 3.
The pathology is not well understood and it is proposed that the underlying pathogenesis could be due to adrenal gland metaplasia, misplacement of myeloid cells, or embolization of bone marrow 1.
Fatty areas appear hyperechoic, whereas cellular components are hypoechoic.
Usually rounded or lobulated masses with heterogeneous appearance of predominate fat density, however overall density is higher than retroperitoneal fat as it contains hematopoietic tissue 2. Areas of high attenuation may be seen due to hemorrhage or calcification.
T1: intermediate to hyperintense signal
T1C+: soft-tissue components of myelolipomas may show mild enhancement
T2: shows areas of low and high signal
Sulfur colloid scan may demonstrate uptake by the reticuloendothelial elements (myelo-) which is a differentiating feature from liposarcoma 6.
Treatment and prognosis
A fatty mass within the retroperitoneal space presents a diagnostic challenge. When in doubt a biopsy should be performed. No treatment is necessary as it is a benign entity. Malignant degeneration has not been reported so far.