Teaching Case

A 70-year-old male presents to his general practitioner with progressively worsening lower back pain and sciatica over the past four months. Previously, this patient underwent a posterior interbody fusion at L5–S1. Given his history and absence of other clinical abnormalities, the patient was referred to radiology for a CT scan of the lumbar spine.

The CT scan of the lumbar spine revealed a sharply demarcated ovoid mass, measuring 9 cm, located within the right retroperitoneum, lateral to the psoas muscle and caudal to the right kidney. The mass comprised fatty tissue with nodular soft tissue components, without significant enhancement on a subsequent multiphasic abdominal CT (figures 1a and 1b), nor evidence of adenopathy or metastasis or any additional relevant abnormalities in the chest or abdomen.

A hyperechoic solid lesion in the right hypochondrium was seen on ultrasound (Figure 2). In addition, an ultrasound-guided biopsy was performed, and the anatomopathological results showed the presence of adipocytes with haematopoietic tissue consistent with a myelolipoma. Surgical removal was planned due to the patient’s symptoms.

Background

Myelolipoma is a benign lesion, classified as a choristoma, characterised by the presence of mature adipose tissue, intermixed with haematopoietic elements (myeloid and erythroid precursor cells) [1–4]. Myelolipomas have a low incidence of 0.08–0.4% and are typically discovered as a unilateral incidentaloma in the adrenal gland. Approximately 12% of cases present bilaterally, and about 15% of myelolipomas are found extra-adrenally [4].

Clinical Perspective

Patients with myelolipoma are generally middle-aged to elderly, with a median age for myelolipoma being 66.5 years. There is a female predilection with a 2:1 female-to-male ratio [3]. Most patients will remain asymptomatic; however, larger lesions may cause symptoms due to mass effect or haemorrhage [2–4]. Importantly, myelolipomas do not possess malignant potential [2–4].

Imaging Perspective

Imaging reveals a well-circumscribed fat-containing lesion, usually located in the adrenal gland, but occasionally found within the pelvis or retroperitoneum, or even in the thoracic cavity. Extra-adrenal adenoma usually ranges between 2–6 cm in size. Ultrasound, CT and MRI can all show the fatty components. Although liposarcoma will often have more irregular edges, differential diagnosis on imaging alone may be challenging or impossible. Findings in inflammatory abdominal fat pathology—such as omental infarctions or epiploic appendagitis—can have a similar look to a heterogeneous lipomatous mass, although these cases will often be symptomatic. Imaging-guided biopsy can be performed to confirm the diagnosis; however, for presacral lesions, biopsy is controversial due to an increased risk of tumoural seeding in the case of liposarcoma [2,3].

Outcome

In asymptomatic patients, myelolipoma is considered a no-touch lesion due to the absence of malignant potential. Surgical removal is indicated if the lesion causes significant symptoms due to mass effect or haemorrhage. There have been no reports of recurrence after surgery [4].

Teaching Points

Extra-adrenal myelolipoma is a rare benign mass, that might be difficult to distinguish from liposarcoma based solely on imaging. In doubt, an imaging-guided biopsy can confirm the diagnosis, and surgical treatment is dependent on the presence of relevant symptoms.

All patient data have been completely anonymised throughout the entire manuscript and related files.