A 74-year-old man with a history of coronary artery disease was found in asystolic arrest and was brought to the emergency department at Yale–New Haven Hospital. Despite vigorous resuscitative attempts, the patient died. An autopsy was performed at a postmortem interval of approximately 6 hours. Autopsy confirmed the death as primarily due to atherosclerotic heart disease.
During autopsy, an incidental retroperitoneal tumor measuring 10 × 8 × 5.5 cm was found. The tumor was irregular, encapsulated by a thin membrane, soft, friable, and yellow to tan-brown on its cut surface (Figure 1). The exact anatomical location of the tumor was as follows: the tumor was anterior to the inferior vena cava and infrarenal segment of the aorta, extended inferiorly over both iliac vessels, and superiorly was related to the inferior pole of the kidney. The tumor, located at L3 through S1, was mostly free-floating, except for a fibrofatty pedicle anchored to perivascular fat from around retroperitoneal great vessels. Specifically, no visceral connections could be identified.
Smear preparations from the cut surface revealed a pleomorphic population of cells, including plasmacytoid forms and less differentiated cells with a high nuclear- cytoplasmic ratio (Figure 2). An inflammatory cell population with segmented forms was also present. Rare large cells with multilobulated nuclei with granular cytoplasm were seen (Figure 2, inset; Quik-Dip, Mercedes Medical, Sarasota, Fla). A bland fibroadipose tissue component was easily identifiable. Formalin-fixed permanent sections revealed predominantly mature adipose tissue encapsulated by a thin fibroconnective tissue (Figure 3, inset). Also seen were predominantly small to medium-sized cells in an infiltrative pattern within the fat lobules. The smaller and medium-sized cells had segmented, convoluted, and indented nuclei. A spectrum of cells, ranging from those with high nuclear-cytoplasmic ratios and more open chromatin to those with smaller clumped nuclei and lower nuclear-cytoplasmic ratios, were seen. A clearly visible, mixed inflammatory cell population was also present (Figure 3). Similar to smear preparations, a few large cells with multilobulated nuclei were again identified.
What is your diagnosis?
Pathologic Diagnosis: Presacral Myelolipoma
Myelolipomata are benign tumors composed of mature adipocytes and hematopoietic tissue. Except for the extramedullary location, the histopathology resembles mature bone marrow, with differing proportions of hematopoietic lineage; for example, the tumor illustrated was composed almost entirely of myelopoietic elements. Myelolipomata are commonly found in a retroperitoneal location, arising from adrenal glands,1 but other locations such as presacrum, mediastinum, and the pleural cavity have also been reported. All reported tumors had a benign morphology and clinical course and virtually no metastatic potential. Larger tumors are reported to carry a risk of spontaneous rupture and intractable bleeding.
Extramedullary bone marrow elements are commonly found in organs capable of compensatory hematopoiesis, such as liver and spleen, in neonates. Hematopoietic tissue admixed with mature adipose tissue is, however, a distinct lesion and was described in the early 20th century.2 The reported frequency of incidental myelolipomata at autopsy is 0.08% to 0.2%.3 No satisfactory explanation has been given for the presence of hematopoietic elements in lipomatous tumors. Two of the hypotheses attempting to explain the histogenesis of this lesion include possible embryonic rests or marrow tissue embolism with subsequent hypertrophic or autonomous growth.
The differential diagnosis of myelolipomata includes angiomyolipoma (in extremely vascular tumors) and extramedullary hematopoiesis in soft tissues. Angiomyolipomas contain vascular and leiomyomatous elements in addition to adipose tissue. Extramedullary hematopoiesis in soft tissues is usually a response to a primary pathology (such as myeloproliferative disorders or hemolytic anemia) and differs from myelolipoma by the involvement of other organs of hematopoiesis (liver, spleen), lack of encapsulation, and lack of lipomatous elements.
Imaging studies do not always distinguish a benign lipomatous lesion from other common retroperitoneal tumors of soft tissue or lymphoid origin (sarcomas and lymphomas). Fine-needle (image-guided) aspiration cytology can play a significant role in diagnosis of this lesion if the lesion is approachable.4,5
Cytopathologic diagnosis of these tumors is aided by the recognition of myeloid precursors in fatty tissue, especially if admixed with megakaryocytic and erythroid lineage cells. Newer surgical techniques, such as laparoscopic surgery, can be useful in managing these lesions. In general, smaller lesions (<4 cm) confirmed by cytology to be myelolipomas can be managed by careful follow-up, and larger lesions (>4 cm) can be removed to avoid risk of spontaneous rupture and hemorrhage.3
In this particular patient, the tumor remained asymptomatic and was detected incidentally at autopsy. In this day of multimodal approaches to early screening and management by aggressive intervention, this incidentally detected tumor at autopsy affords a fascination for the morbid anatomists who tend to wonder if the patient may have lived so long if this was detected earlier.
References
The authors have no relevant financial interest in the products or companies described in this article.
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