Case In Point: Peripheral nerve sheath tumor mimicking pulmonary embolism

The case

A 63-year-old man presented to the emergency department with a 1-week history of dyspnea and pleuritic chest pain. Two months earlier, he had undergone an uncomplicated laparoscopic cholecystectomy. A spiral CT scan of the chest showed a filling defect obstructing the entire left main pulmonary artery, which was interpreted as PE (Figure 1).

Echocardiography showed an estimated pulmonary artery pressure of 45 mm Hg. The patient received thrombolytic therapy (alteplase 10-mg bolus followed by a 90-mg intravenous infusion over 2 hours) followed by heparin, with marked improvement. He was discharged home after 6 days of oral anticoagulation therapy.

Two months later, the patient presented again with increased dyspnea and chest pain. He also complained of back pain, which he attributed to muscle spasm. On physical examination, his vital signs were stable and he was alert and oriented. Heart rate was regular without any murmurs, and lungs were clear to auscultation with decreased air entry at the left base. Musculoskeletal examination revealed a large, tender, firm, and nonfluctuating mass in the left paraspinal region in the area of the lower thoracic vertebrae with an approximate size of 7 3 5 cm.

CT angiography showed dilatation of the left pulmonary artery and a tumor extending down to subsegmental levels distally and into the main pulmonary artery proximally (Figure 2). There also were multiple pulmonary and pleural masses indicative of metasta- tic disease. The paraspinal mass, measuring 7.7 3 6 cm, was erod-ing the adjacent rib and vertebral body pedicle at the T11 level (not shown). Except for the left pulmonary artery filling defect, all of the masses were new compared with the CT findings obtained 2 months earlier.

The results of surgical biopsy of the paraspinal mass were consistent with "high-grade sarcoma, most consistent with malignant peripheral nerve sheath tumor" (Figure 3). Immunohistochemical stains showed reactivity in tumor cells for vimentin, S-100, and CD 57, but no reactivity was seen for desmin, smooth muscle actin, cytokeratin, CD 31, CD 34, or factor VIII antigen.

After the limited therapeutic options and poor prognosis were discussed with the patient and his family, they elected to proceed with a conservative approach and comfort care. The patient died 12 days after admission, and the family refused an autopsy.

Discussion

Nerve sheath tumors are tumors arising from the stromal or supportive cells of the peripheral nerves, including Schwann cells, perineural cells, and fibroblasts. Tumors of nerve sheath origin in the mediastinum are predominantly benign, similar to schwannomas and neurofibromas.

The malignant neurosarcomas are much less common than the benign tumors. They account for 10% of all soft tissue sarcomas¹ and are seen most commonly in the head, neck area, and extremities. An intrathoracic malignant peripheral nerve sheath tumor is rare² and arises from the nerve trunks in the posterior mediastinum or the vagus, phrenic, or other peripheral nerves.

Mediastinal neurofibromas are strongly associated with neurofibromatosis-1 (von Recklinghausen disease).^2,3 There also is an increased incidence of malignant peripheral nerve sheath tumors in patients who have this disease (4.6%, compared with 0.001% in the general population).⁴

Macroscopically, malignant peripheral nerve sheath tumors are often large, partly necrotic, and hemorrhagic tumors, with a tendency to spread within the parent nerve. Most commonly, they originate from the neurofibromas. The anaplastic transformation of the schwannomas is very rare.

The microscopic appearance is extremely variable. They can be composed of spindle cells with pleomorphic nuclei and multiple mitotic figures or can have epithelioid variants that mimic carcinoma. Rarely, they show differentiation toward skeletal muscle and are called Triton tumors. Bone, cartilage, and epithelial tissue are the other rare forms of differentiation.

Malignant peripheral nerve sheath tumors are aggressive tumors that frequently infiltrate the neighboring structures. Lung, liver, bone, skin, and serous surfaces are common sites of metastasis. Patients may present with mass effect resulting from the tumor, anorexia, weight loss, fatigue and, occasionally, fever. They also may have distant metastasis at presentation. MRI is the diagnostic modality of choice.¹

Treatment consists of complete surgical excision and postoperative radiation therapy.^1,5 These tumors are very resistant to chemotherapy. They are frequently associated with metastasis and recurrence, and the long-term prognosis is poor.

Poor prognostic factors include tumor size greater than 5 cm, more central location, and association with neurofibromatosis. Histolog-ic grading is not very helpful for prognosis.⁴

In conclusion, malignant peripheral nerve sheath tumors are rare, aggressive tumors. Intrathoracic presentation of the tumors is uncommon and is associated with neurofibromatosis-1. There are a few reported cases of intrathoracic malignant tumors that developed without any stigmata of neurofibromatosis.⁶ To the best of our knowledge, this is the first published case of malignant peripheral nerve sheath tumor that presented mimicking PE not associated with neurofibromatosis.

References:

REFERENCES

1. Baehring JM, Betensky RA, Batchelor TT. Malignant peripheral nerve sheath tumor: the clinical spectrum and outcome of treatment.

Neurology

. 2003;61:696-698.
2. Kim JG, Sung WJ, Kim DH, et al. Malignant peripheral nerve sheath tumor in neurofibromatosis type I: unusual presentation of intraabdominal or intrathoracic mass.

Korean J Intern Med

. 2005;20:100-104.
3. Leroy K, Dumas V, Martin-Garcia N, et al. Malignant peripheral nerve sheath tumors associated with neurofibromatosis type 1: a clinicopathologic and molecular study of 17 patients.

Arch Dermatol.

2001;137: 908-913.
4. Ducatman BS, Scheithauer BW, Piepgras DG, et al. Malignant peripheral nerve sheath tumors. A clinicopathologic study of 120 cases.

Cancer

. 1986;57:2006-2021.
5. Nambisan RN, Rao U, Moore R, et al: Malignant soft tissue tumors of the nerve sheath origin.

J Surg Oncol.

1984;25:268-272.
6. Ogino H, Hara M, Satake M, et al. Malignant peripheral nerve sheath tumors of intrathoracic vagus nerve.

J Thorac Imaging

. 2001;16:181-184.