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* From Lenox Hill Hospital, New York, NY.
Correspondence to: Varghese Cherian, MD, MS, Lenox Hill Hospital, 100 East 77th St, New York, NY 10021; e-mail: vcherian{at}lenoxhill.net
A 61 -year-old, white woman presented to the emergency department with abdominal pain of several days duration. She complained of having loose bowel movements almost thrice daily for approximately 2 to 3 weeks. She reported decreased oral intake and diffuse joint pains. She denied any fever or chills as well as nausea or vomiting. Despite her loose bowel movements, she claimed recent weight gain over the past few months of approximately 10 lb. Her medical history was remarkable for Crohn disease and osteoporosis. She had previously twice undergone surgery for small bowel obstruction. Her surgical history also included cholecystectomy, appendectomy, and herniorrhaphy. She denied any history of smoking.
Physical examination revealed an afebrile, well-nourished, white woman with no acute distress. Her BP was 111/60 mm Hg, with a pulse rate of 76 beats/min and a respiratory rate of 20 breaths/min. Examination of the cardiovascular system revealed 3/6 systolic murmur radiating to the neck and bilateral carotid bruits. The lungs were clear to auscultation. The abdomen was mildly tender and slightly distended with diminished bowel sounds. Bilateral lower-extremity pitting edema was noted. Blood analysis revealed hemoglobin and hematocrit levels of 8.7 g/dL and 25, respectively. The WBC count was not elevated. Her coagulation profile was within normal limits. Electrolytes, amylase, and lipase levels were also all within normal range. Further laboratory workup showed evidence of hemolytic anemia. A posteroanterior view of the chest showed clear lungs and no effusions (Fig 1 ). Her chest radiograph was notable, however, for several fairly well-marginated opacities identified bilaterally along the lower thoracic spine. CT of the chest, abdomen, and pelvis was obtained to further evaluate those densities and the cause of the abdominal pain. CT confirmed several posterior mediastinal masses in a paravertebral distribution bilaterally (Fig 2, 3 ). The largest mass measured 2.5 x 1.9 cm at the T10/11 level in the left paravertebral region. Abdominal images demonstrated few dilated small bowel loops and noncontinuous areas of wall thickening involving the mid-transverse, descending, and sigmoid colon. CT-guided percutaneous needle biopsy was performed of the largest left paravertebral mass (Fig 4 ).
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Diagnosis: Posterior mediastinal pseudotumors due to extramedullary hematopoiesis secondary to Crohn disease and hemolytic anemia.
Fine-needle aspirate showed hematopoietic cells characterized by presence of megarkaryocytes, erythroblasts, and lymphoid lineage cells (Fig 5
). Flow cytometry revealed those lymphoid cells to be of predominantly T-cell lineage.
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Multiple paravertebral masses may develop secondary to abnormal hypertrophy of hematopoietic tissue. Those paraspinal masses are usually located below the level of the sixth thoracic vertebra. Diagnostic features of posterior mediastinal extramedullary hematopoiesis on plain radiographs may include unilateral or bilateral smooth, lobulated masses. CT may demonstrate similar findings of well-circumscribed soft-tissue density pseudotumors in a paraspinal distribution. There should be no evidence of bony erosion involving the vertebral bodies or ribs. No intralesional calcification should be seen. Adipose tissue, however, may be present within these masses. MRI may also be used to establish the diagnosis by identifying adipose tissue or demonstrating thoracic rib expansion without evidence of cortical bone erosion. Extramedullary hematopoietic masses usually demonstrate low signal on both T1 and T2 weighted images, with intermediate enhancement after contrast administration. Replacement of the fatty marrow by hematopoietic marrow may manifest as low to intermediate signal within the vertebral bodies. Radionuclide bone scintigraphy using 99mTc sulfur colloid or 111In is another noninvasive method to make the diagnosis.56 Focal uptake of the tracer localizing to paravertebral masses in the appropriate clinical setting is confirmatory. Tissue sampling, as in this case, may be required in equivocal cases or when malignancy cannot be entirely excluded.
Extramedullary hematopoiesis is not a common cause of posterior mediastinal masses. Differential considerations for posterior mediastinal masses include neoplastic, infectious, and hereditary or acquired etiologies. Benign neoplastic causes consist of neurogenic tumors largely of peripheral nerve origin such as schwannoma and neurofibroma, or of sympathetic ganglia origin such as ganglioneuroma. Benign bone tumors of the spine such as aneursymal bone cyst or fibrous dysplasia may also be considered. Mesenchymal tumor, hemangioma, or lymphangioma are less likely. Malignant neoplasms include metastases, lymphoma, multiple myeloma, and Ewing sarcoma. Infectious etiologies that may produce a pseudotumor are likely to be of mycobacterial or fungal origin such as tuberculosis, nocardia, or actinomyces. Lateral meningocele, as may be manifested in neurofibromatosis I, bronchogenic cyst, Bochdalek hernia, and aortic aneurysm/pseudoaneurysm are several hereditary or acquired causes of posterior mediastinal masses.
Extramedullary hematopoiesis develops slowly over time and is usually asymptomatic. However, complications have been reported secondary to mass effect or spontaneous rupture. Symptomatic pleural effusions and fatal massive hemothorax have been attributed to extramedullary hematopoiesis.7 Epidural extramedullary hematopoiesis can lead to paraplegia secondary to spinal cord compression.8 Intracranial extramedullary hematopoiesis was implicated as the cause in a patient with generalized epileptiform seizures.9 Cases of small bowel intussusception and obstructive uropathy due to extramedullary hematopoiesis have also been reported.1011 Hematopoetic tissue is very radiosensitive. Radiation therefore, may be utilized to decrease the size of masses in certain complicated cases and may obviate the need for surgical intervention. Hydroxyurea has also been shown to be effective in treatment of symptomatic extramedullary hematopoiesis.12 Hypertransfusion is another method that has been successfully used to reduce mass size.13
The patient received 2 U of packed RBC transfusion to elevate the hemoglobin level. The Crohn disease exacerbation was treated with oral steroids and mesalamine. There was a favorable response to the provided therapy. No additional treatment was required for her asymptomatic paraspinal extramedullary hematopoiesis. The patient had an uncomplicated hospital course and was discharged home on continued steroid and mesalamine regimen.
Extramedullary hematopoiesis is a differential consideration for posterior mediastinal masses. Conditions that predispose to suboptimal tissue oxygenation such as hemoglobinopathies and myleoproliferative disorders are most commonly associated with extramedullary hematopoiesis. Severe anemia due to chronic illnesses such as Crohn disease may provide the impetus for extramedullary hematopoiesis. Posterior mediastinal masses in a paraspinal distribution in a patient with severe anemia should alert the clinician to the possible diagnosis of extramedullary hematopoiesis. Several imaging modalities including plain or digital radiographs, CT, and MRI may demonstrate the characteristic features of extramedullary hematopoiesis presenting as paravertebral masses. Radionuclide scanning and tissue sampling can be used to confirm the diagnosis.
Footnotes
The authors have no conflicts of interest to disclose.
Received for publication November 14, 2006. Accepted for publication March 1, 2007.
References
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