Applied Radiology

CASE SUMMARY:

A 74-year-old man underwent CT scanning of the chest, abdomen, and pelvis for evaluation of gastrointestinal bleeding. Two paraspinal masses unrelated to the aorta were discovered (figure 1). The patient had a remote history of splenectomy for hemolytic anemia and has chronic anemia. Magnetic resonance imaging at 1.5 T was performed in an attempt to narrow the differential diagnosis among neural tumors, metastases, mesenchymal tumors, hematomas, developmental cysts, or extramedullary hema-

topoiesis (EMH), and less likely possibilities including para-

spinal abscesses, and pseudo-

meningoceles.

DIAGNOSIS:

Extramedullary hematopoiesis.

Conventional spin echo MRI demonstrated the masses and the marrow of the adjacent vertebral body to have the same signal characteristics on all pulse sequences. This indicates they are composed of identical material. Conventional spin echo imaging (as opposed to fast spin echo imaging) was used to better demonstrate the signal of the fatty elements in the marrow and the masses.

DISCUSSION:

Patients do not have significant extramedullary hematopoiesis at birth. However, when stimulated, such as during severe hemolytic anemia, Hodgkin's disease, or bone marrow failure (from metastatic

disease, poisoning, myeloid metaplasia, irradiation and infection), mesenchymal cells resume active hematopoiesis.1 The most common sites are in the liver, spleen, and lymph nodes.2 Most often these present radiographically as asymptomatic masses.

Nuclear medicine bone marrow imaging studies may suggest this diagnosis, but MRI, due to its multiplanar capability, variable pulse sequences, and the use of contrast agents, is much better at characterizing the masses and differentiating among the radiographic possibilities. MRI can show enhancement and possible neural foraminal extension in neural tumors, the non-enhancing characteristics of cysts, the adjacent inflammation related to abscesses, the unique signal characteristics of hematomas, and the communication with the dural sac in pseudomeningoceles.

In this case, the history, and slight heterogeneity of the masses (suggesting the presence of fat) on CT suggested the diagnosis. MRI narrowed the differential diagnosis to EMH and diffuse involvement of bone marrow and paraspinal lymph nodes by metastatic disease. The lack of a known primary tumor, the lack of brightening on the T2-weighted images, and the suggestive clinical history lead to the diagnosis of EMH. As expected, follow-up at 5.5 months demonstrated no interval change. MRI is helpful in confirming this diagnosis and avoiding the possible complications during biopsy of these vascular masses.

References

1. Wyngaarden JB, Smith LH, Jr. (eds): Textbook of Medicine, 17th ed, p 944. Philadelphia, Cecil, 1982.

2. Kouraklis G, Dosios T: Intrathoracic extramedullary hematopoieses simulating tumor in a patient with sickle cell anemia. Eur J Cardiothorac Surg 8(4):220-221, 1994.

3. Kumar A, Aggarwal S, de Tilly LN: Case of the season. Thalassemia major with extramedullary hematopoiesis in the liver. Semin Roentgenol 30(2):99-101, 1995.

4. Lau SK, Chan CK, Chow YY: Cord compression due to extramedullary hematopoiesis in a patient with thalassemia. Spine 19(21):2467-2470, 1994.

5. Boyacigil S, Ardic S, Tokoglu F, et al: Intrathoracic extramedullary hematopoiesis. Australas Radiol 40:179-181, 1996.

6. Kalina P, Wajih Z, Drehobl KE: Cord compression by extramedullary hematopoiesis in polycythemia vera (letter). AJR 164:1027-1028,

1995.

Prepared by Joel M. Schwartz, MD, Attending Radiologist, Nyack Hospital, Nyack, NY.