A 32-year-old man presented to the emergency department of our institution following acute onset of fever in the setting of a one-week history of left lower quadrant abdominal pain. The patient was known to have a personal and family history of multiple endocrine neoplasia type IIA syndrome, and had undergone total thyroidectomy at the age of five for medullary carcinoma, and bilateral adrenalectomy at the age of ten for bilateral pheochromocytomas. On examination the patient was febrile, and his physical exam was significant for left lower quadrant abdominal tenderness, otherwise unremarkable. Laboratory testing revealed elevated white blood cell count (12300/mm3) and increased proportion of neutrophils on differential analysis (75% neutrophils). Results of other routine hematologic tests, electrolyte levels and renal function were normal.
Given the patient's history, physical examination, and laboratory findings, CT scan of the abdomen and pelvis with intravenous and oral contrast was ordered for evaluation of possible diverticulitis and to rule out other gastrointestinal, renal, and urologic disease. CT scan demonstrated the presence of acute sigmoid diverticulitis; incidentally, two large mass lesions in the omentum containing both soft tissue and fat components were identified (). One lesion measured 11.4 × 10 × 11 cm (in the transverse, anteroposterior, and craniocaudal dimensions respectively) and the other measured 12 × 9 × 13.6 cm (in the transverse, antero-posterior, and cranio-caudal dimensions respectively).
Figure 1 32-year-old male patient with multifocal extra-adrenal myelolipoma. A, B: Axial contrast enhanced (IV and PO) CT images through the mid abdomen obtained in the equilibrium phase show two large well circumscribed soft tissue masses containing significant (more ...)
The patient was subsequently treated with intravenous antibiotics and diet modification over the course of 3 days with resolution of symptoms.
The significance of the omental masses was unclear and it was considered unlikely that the masses are related to the resected adrenal pheochromocytomas, twenty two years ago. Prior to discharge the patient underwent percutaneous CT-guided biopsy and the pathological differential diagnosis included extra-adrenal myelolipoma, extramedullary hematopoiesis, sclerosing extramedullary hematopoietic tumor, and angiomyolipomas.
The decision was then made by the patient and his care team to follow the masses for progression, regression, and disease potential with hematologic laboratory evaluations, physical exams, and serial CT imaging at regular intervals. A follow-up CT examination after a 5-month interval demonstrated stability of the omental masses. Throughout this time the patient remained asymptomatic without any sign of myeloproliferative disease. Three months later the masses were laparoscopically resected for definitive pathologic diagnosis. One mass measured 14 × 12 × 8 cm, weighed 650 grams, and was attached to a segment of omental fat measuring 14 × 5 × 2 cm (). Another mass measured 14 × 10 × 7.5 cm, and was attached to a 41 × 18 × 3 cm segment of omentum. The masses were encapsulated, yellow-tan to red in color, nodular in appearance, and solid on cut sections without evidence of necrosis. The sections revealed mature adipose tissue with intermingled hematopoietic cells representing all three lineages of hematopoiesis (). These morphological features are most consistent with a myelolipoma. Flow cytometry showed no evidence of leukemia or lymphoma. There were no additional masses or lymph nodes found in the omentum. The final pathologic diagnosis of extra-adrenal myelolipoma was made. In the interim, two years have elapsed and the patient is in good health without any sequela attributed to the extra-adrenal myelolipomas.
Figure 2 32-year-old male patient with multifocal extra-adrenal myelolipoma. Gross appearance of the surgically resected extra-adrenal myelolipoma with yellow areas (black cursors) containing adipose tissue admixed with hemorrhagic foci consistent with bone marrow (more ...)
Figure 3 32-year-old male patient with multifocal extra-adrenal myelolipoma. Extra-adrenal myelolipoma showing normal adipocytes (arrows) with normal maturing myeloid, erythroid, and megakaryocytic lineages (hematoxylin-eosin, original magnification × (more ...)