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Clinical Pathological Correlations > Current Correlation > Diagnosis and Discussion

The patient is a 53-year-old man who presented to an outside hospital with a 3-day history of nausea and vomiting, followed by diarrhea.

An abdominal CT scan showed a 25 x 18 cm abdominal mass and an MRI was later performed to better define the lesion. The impression was that of a large retroperitoneal mass with fat and soft tissue components exerting a mass effect on the right kidney, right adrenal, and right hepatic lobe consistent with a liposarcoma (Figure 1). There were also two incompletely visualized T2-hypointense lesions in the right kidney, the largest measuring approximately 2.2 x 1.5 cm. The right adrenal gland was not visualized.

After further clinical work up, the retroperitoneal mass was resected and a right nephrectomy was performed. The specimen was sent to Surgical Pathology for evaluation. It consisted of 4,200g, smooth, tan-gray encapsulated mass with no evidence of tumor extension through the fibrous capsule. The mass was sectioned to show a heterogeneous, tan-orange, glistening yellow and brown cut surface with scattered areas of hemorrhage (Figure 2). The kidney was sectioned to show multiple tan-yellow, well circumscribed, firm masses that ranged between 0.3 cm and 1.5 cm. Representative H&E sections of the large soft tissue mass are shown in Figures 3 and 4 and of the renal masses in Figure 5.


Figure 1


Figure 2


Figure 3


Figure 4


Figure 5

Diagnosis:

Adrenal myelolipoma and papillary renal cell carcinoma, Fuhrman grade 2 of 4; Type 1.

Discussion:

Myelipoma is a rare, benign tumor composed of mature adipose tissue and bone marrow elements predominantly detected in the 5th-6th decades of life and occurring equally in men and women. Based on autopsy studies, its incidence is approximately 0.08-0.2%. Although the exact cause of myelolipoma is not known, it is associated with obesity, hypertension, and other chronic illnesses. It is not thought to be associated with hematopoietic or other malignancies.

Histologically, myelolipomas consist of lipocytes and hematopoietic elements in varying proportions. It is not considered a true extramedullary hematopoietic tumor, however, as its presence is not indicative of any abnormality in the patient's actual bone marrow. Most have trilineage hematopoiesis and complete maturation in erythroid and myeloid series, with increased megakaryocyte counts compared to normal bone marrow. Unlike normal marrow, however, the overall cellularity in is independent of patient age. Some tumors can have extensive myxoid change.

Myelolipomas are most frequently detected as a small (< 4 cm), unilateral mass in the adrenal gland, but has also been reported in extra-adrenal retroperitoneum, presacral sites, thoracic cavity and lung, mediastinum, liver, spleen, and testis. In the adrenal gland, they are sometimes associated with hormonally active neoplasms, including adrenocortical adenomas, adrenocortical carcinomas, and pheochromocytomas. Clinically, it can be associated with adrenocortical hyperplasia, Cushing's disease, 21-hydroxylase and 17-?-hydroxylase deficiency, and Conn's syndrome. When small, myelolipomas are usually asymptomatic. When detected, they are often incidental on imaging, during surgery or at autopsy. However, these tumors can grow to be quite large, termed "giant" myelolipoma. They have been reported to weigh up to 4000-6000 g and measure up to 34 cm. Large tumors become symptomatic by mass effect on surrounding structures. Rupture with massive retroperitoneal hemorrhage after minor trauma has also been reported.

Because myelolipomas are often radiologically detected as "incidentalomas" in the retroperitoneum, their differential diagnosis includes other lipomatous tumors: lipoma, angiolipoma, and liposarcoma. On CT imaging, myelolipomas appear as a well-demarcated, heterogeneous masses with low-density mature fat interspersed with more mature myeloid tissue. If they are detected in the adrenal gland, they can be differentiated from adrenal adenoma by their lesser density and greater heterogeneity. As compared to the more infiltrative liposarcoma, myelolipomas often have a discrete capsule. Ultrasonography reveals well-defined, hyperechoic areas (fat) with hypoechoic regions (myeloid). Spin-echo pulse sequence MRI shows a signal intensity equal to subcutaneous and retroperitoneal fat. MRI does not significantly add to the radiological characterization of these tumors, but can help in the assessment of tissue planes for surgical planning. Fine-needle aspiration can rule out malignancy by presence of mature adipocytes and hematopoietic elements, which are diagnostic of myelolipoma.

Management is dictated by actual or potential symptoms that occur mainly due to mass effect. Resection is recommended by some authors when lesions reach >10 cm. They do not recur after surgical resection.

Only a very few reports of concurrent adrenal myelolipoma and renal cell carcinoma of any type are found in the literature. Thus, the association here with papillary renal cell carcinoma is likely just incidental.