Myelolipoma is a benign and non-functional tumor that predominantly develops in the adrenal gland. It was first described by Gierke in 1905 [1]. It was considered rare and an incidental autopsy finding with reports of only 300 cases by 2000 [2]. With computed tomography (CT), and magnetic resonance imaging (MRI); it became more common, constituting up to 10% of 4% incidental adrenal masses (incidentaloma) [3]. It is a form of metaplasia, in the gland, that leads to formation of mature adipose tissue and scattered islands of hematopoietic elements, resembling bone marrow [4]. The tumor is usually small and asymptomatic. However, its thin-walled vascular channels lined by a single layer of endothelial cells may exhibit bleeding in some cases that leads to loin pain and rapid enlargement that may culminate with catastrophic intraperitoneal rupture and shock [5]. Elective surgery can prevent a more severe symptom presentation and life-threatening progression and allows accurate diagnosis in patients with tumors larger than 6 cm [6]. In this case report, we present a patient with symptomatic and large myelolipoma that indicated surgery for symptomatic relieve and definite diagnosis.

A 71-year-old man presented with dull-aching left loin pain for two months. Past history was significant for diabetes mellitus and hypertension for 15 years. Moreover, he had mild renal impairment for four years. His medications included: Alpha methyl-dopa, Amlodipine, insulin, statin, and Furosemide. The patient was short and obese with weight at 100 kg. Blood pressure was normal and he did not have peripheral edema. Systemic examination did not show abnormality. Laboratory investigations showed elevated serum creatinine at 240 umol/L and low albumin at 32 g/L with proteinuria. Thyroid function and serum (TSH), serum electrolytes, and liver function tests were normal. Hemoglobin was low at 110 g/L with normal transferrin saturation % and vitamin B12. Ultrasound of the abdomen revealed a large heterogenous mass at the upper pole of the left kidney. Computed tomography scan of the abdomen showed it to be well-defined lesion with adipose tissue (CT density—16 Hounsfield units) and foci of calcifications. It measured 65, 6×6, and 6×6 cm in anteroposterior (AP), transverse (TV), and craniocaudal (CC) dimensions, respectively (Figure 1). ¹⁸F-FDG-PET/CT scanning form vertex to mid-thigh showed hypermetabolic activity only at the rim of the mass (SUV_max 4.0) with non-avid hypodense center (Figure 2). Hormonal tests showed normal AM Cortisol, adrenocorticotropic hormone (ACTH), and low-dose Dexamethasone suppression tests. Serum as well as 24-hour-urine for catecholamines, renin-aldosterone ratio, dehydroepiandrosterone sulfate (DHEAS), and testosterone. The latter findings were not in favor of (a) functioning tumor and (b) malignancy. However, left adrenalectomy was advised since the patient was symptomatic and medically stable as well as for definite diagnosis and cure. Conventional extraperitoneal approach was used since the tumor was large and surgery went without complications. On gross appearance, the left adrenal mass was partially covered with fibrofatty tissue, weighing 153 g and measuring 110×75×42 mm (Figure 3A). On sectioning, a pale yellow to brown encapsulated and well-circumscribed tumor was seen measuring 60×52×35 mm with foci of hemorrhage, necrosis, and cystic degeneration. The tumor was seen surrounded by a thin rim of normal-appearing golden yellow adrenal cortical tissue (Figure 3B). Microscopic examination showed a well-circumscribed lesion with a thin rim of normal appearing adrenal cortical tissue. It was mostly of organizing hematoma and in parts of variably vascular channels lined by a single layer of endothelial cells filled with blood and surrounded by fibrous tissue, islands of mature adipose tissue admixed with bone marrow elements including megakaryocytes, foci of osseous metaplasia, and dystrophic calcification (Figure 4A, Figure 4B, Figure 4C). There was no evidence of high-grade nuclear changes and increased mitotic activity. Moreover, there were smooth muscle elements akin to angiomyolipomata. Hence, the final diagnosis was consistent with large myelolipoma.

Adrenal tumors (masses) are common with 10% prevalence in autopsy cases. They are subdivided into: (a) benign tumors, viz. adenoma, myelolipoma, neurofibroma, and hyperplasia; (b) malignant tumors, viz. adrenal carcinoma and neuroblastoma; and (c) metastatic tumors. Only 10% of pheochromocytoma are malignant. Adrenocortical adenoma is the most common lesion (52%) followed by carcinoma (12%), pheochromocytoma (11%), myelolipoma (8%), and metastasis from lung, breast, and gut (2%). A minority (<15%) of both benign and malignant lesions are functional, meaning they overproduce their respective hormones. These include cortisol, aldosterone, and DHES from adenomas and carcinomas, as well as catecholamines from medullary tumors such as pheochromocytomas and neuroblastomas [7]. Management of adrenal tumors requires close coordination among professionals from various medical fields. The majority (75%) of adrenal tumors are nonfunctioning, benign adenomas, and often do not require surgical intervention [8]. On the other hand, surgery is indicated in functioning benign and/or malignant adrenal tumors and metastases [9]. Functioning tumors overproduce cortisol (Cushing syndrome), aldosterone (Conn’s disease), catecholamines (pheochromocytoma), and sex-steroid hormones (hyperandrogenism) [10]. For decision-making in management, three steps were indicated: (a) exclusion of functioning tumor, (b) exclusion of benign incidentaloma by abnormal CT findings, and (c) assessment for hypermetabolism in the mass indicative of malignancy. In this patient, with moderate renal disease, CT scan with contrast was not done to avoid contrast-induced nephropathy. Moreover, MRI with gadolinium-based dye was not done to avoid, in this patient with severe renal failure, nephrogenic systemic fibrosis. Enhancement of masses, following with CT and MRI dyes, is a valuable sign of malignancy. Hence, such third step was replaced by PET scanning. The existence and distribution of hypermetabolism in the masses is an alternative sign of malignancy in absence of infections. In our patient, hypermetabolism was limited to the rim only. Based on the above-mentioned data, the patient had (a) well-defined tumor borders, (b) foci of calcifications, and (c) rim hypermetabolism, which were more in favor of bleeding in a large myelolipoma rather than necrotizing malignant neoplasm [11]. Foci of calcifications, due to previous degeneration or differentiation of choristomatous primitive mesenchymal cells, have been reported in 25% of myelolipomata [12],[13]. Notably, though reported, fine needle aspiration is associated with inadequate tissue for diagnosis and core one with bleeding and seeding [14]. However, since the (a) tumor was large, (b) patient was acutely symptomatic (from bleeding), and (c) patient was not high-risk for surgery; surgery was advised to establish definite diagnosis and permeant cure. Histological examination ruled out malignancy, viz. liposarcoma, myxoid liposarcoma, and myofibrosarcoma as well as angiomyolipoma [15].

Myelolipoma diagnosis requires hormonal testing, CT/MRI scans, and PET study with individualized management tailored to each case.