Diagnosis of benign solitary fibrous tumors by positron emission tomography.

Abstract: An 80-year-old male presented with dyspnea so severe that he could not perform the activities of daily living. Chest radiography and computed tomography of the chest demonstrated a 30-cm left chest mass extending inferiorly to displace the left kidney and spleen. Three incisional biopsies yielded inconclusive results. Positron emission tomography (PET) with fluorodeoxyglucose F 18 (FDG) ruled out malignancy, so a curative excisional biopsy was performed. We conclude that FDG PET is a crucial component of the initial evaluation of patients with solitary pulmonary masses. FDG PET has high sensitivity, specificity, positive predictive value, and negative predictive value in the diagnostic clarification of radiologically indeterminate pulmonary lesions.

Key Words: dyspnea, emission-computed tomography, fluorodeoxyglucose F 18, pleural mesothelioma, x-ray computed tomography

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A solitary intrathoracic, pleura-based mass in an older patient presents a challenge to clinicians. The differential diagnosis includes benign and malignant mesothelioma, metastatic tumor, schwannoma, neurofibroma, lipoma, hematoma, mesothelial cyst, empyema, and effusion. Since accurate diagnosis is a crucial requisite for effective intervention, precise tools to quickly ascertain the underlying pathophysiology are welcome. Positron emission tomography (PET) with fluorodeoxyglucose F 18 (FDG) is a noninvasive technique to both (1) stage non-small cell carcinomas of the lung (1) and (2) determine the malignant potential of solitary pulmonary nodules. (1-3) The glycolytic activity of masses can be assessed by means of PET to estimate the likelihood of the presence of a malignant process. (1,2) We report the diagnostic value of FDG PET in the case of an 80-year-old male with a large tumor of the thorax of unknown cause.

Case Report

An 80-year-old male presented with progressive dyspnea of several years' duration. He also reported chronic fatigue, weakness, and anorexia. Despite the administration of home oxygen therapy, he gradually became wheelchair bound and unable to perform the activities of daily living. His medical history included diet-controlled diabetes mellitus, exogenous obesity, chronic renal insufficiency, hypothyroidism, and gout. His social history was significant for heavy smoking (40 pack-years). He also had a long history of asbestos exposure. Radiographic evaluation revealed a left peripheral thoracic mass. Because of the high index of suspicion that this enlarging basal mass was a mesothelioma, a course of radiotherapy was administered a decade previously. Although three separate biopsies of the left chest mass were performed, they were of no use in establishing a definitive diagnosis. The differential diagnosis included either a mesothelioma or a benign fibrous tumor.

Because of the incapacitation caused by his progressive symptoms, he underwent further evaluation. A left lower hemithorax mass on chest radiography was confirmed by computed tomography (Fig. 1). To determine if he had a mesothelioma or a benign fibrous tumor, PET was recommended.

He was referred for PET in order to evaluate the lung mass and resolve the differential diagnosis, which included organized empyema, metastasis of an unknown primary malignancy, local benign mesothelioma, subpleural lipoma, hematoma, mesothelial cyst, neural tumors including schwannoma, neurofibroma, malignant fibrous histiocytoma, and angiosarcoma. (4,5) Whole-body PET, 30 minutes after the intravenous injection of 10 mCi fluorodeoxyglucose F 18, revealed a large heterogeneous mass in the left posterior chest (Fig. 2). This was interpreted as a benign mass. In addition, the uptake of the entire mass was close to the background uptake, a finding suggesting a benign tumor. The heterogeneous uptake was interpreted as tumor necrosis in the mass. The PET scan did not demonstrate a high FDG uptake consistent with mesothelioma or other malignancy. (6)

One month later, the patient underwent surgical resection of the tumor (Fig. 3), which measured 15 X 13 X 17 cm (Fig. 4). The pathology report revealed a pleura-based solitary fibrous tumor with a greatest dimension of 19.5 cm, with benign histologic appearance and areas of cellularity and necrosis.

Discussion

This is a case report of a massive peripheral intrathoracic lesion suspicious for a malignant neoplasm studied by FDG PET and found to be benign, leading to a curative resection.

Primary neoplasms of the pleura are rare. Solitary benign fibrous tumors of the pleura enlarge rapidly and occasionally may transform into malignant forms. (7) Fibrous tumors of the pleura are also called benign mesotheliomas. They occur equally in men and women. They occur in the third to eighth decade of life, with a mean age of onset of 50 to 60 years. They are unrelated to asbestos exposure. Solitary benign fibrous tumors of the pleura arise as a solitary mass from the visceral pleura in 80% of patients, and from parietal pleura in 20%. These tumors of the pleura originate from the submesothelial mesenchymal cells with relatively acellular fibrous tissue. Typically, they are sharply circumscribed lobular masses occurring in the lung periphery adjacent to the pleural surface, and measuring 2 to 30 cm in diameter. (8)

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Solitary benign fibrous tumors of the pleura are asymptomatic in approximately half of cases. Symptoms commonly occur when these tumors of the pleura enlarge to impinge on surrounding structures. The presenting symptoms of these tumors of the pleura include cough, fever, dyspnea, and chest pain. Digital clubbing is a common manifestation. Hypertrophic osteoarthropathy occurs in up to a third of cases. Episodic hypoglycemia occurs in 4% of cases. (4,9) Surgical excision of these tumors renders patients symptom-free.

[FIGURE 4 OMITTED]

The most reliable criterion for malignancy is stromal invasion. (10) Mesothelial proliferations to fat, chest wall muscle, or lung parenchyma are almost always malignant. However, benign and malignant mesotheliomas may be indistinguishable with the use of microscopic pathologic examination for cellular atypia, necrosis, keratin staining, and immunohistochemical staining. (5)

On the other hand, the differentiation of benign tumors and malignant mesotheliomas is facilitated by FDG PET because the FDG uptake in malignant mesothelioma is very high. (6) Although some may question the usefulness of FDG PET to differentiate benign from malignant soft tissue masses, (11) FDG PET is typically helpful to differentiate benign fibrous tumors from malignant mesotheliomas. (6,12) Therefore, whole-body FDG PET is a noninvasive technique to readily and accurately differentiate benign from malignant solitary pulmonary nodules. (3) FDG PET clarifies the diagnosis of radiologically indeterminate pulmonary lesions with high values of sensitivity (92%), specificity (86.6%), positive predictive value (89.4%), and negative predictive value (89.6%). (13) Pathologic diagnosis by biopsy is recommended to confirm FDG PET in pulmonary (14) and pleural lesions. (15)

Conclusion

FDG PET is a crucial addition to the diagnostic armamentarium of clinicians faced with the evaluation and treatment of patients with solitary pulmonary masses. (16)

If you haven't got anything nice to say about anybody,
come sit next to me.
--Alice Roosevelt Longworth

Accepted September 15, 2004.

Please see Ruairi J. Fahy and Mark King's editorial on page 1156 of this issue.

References

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8. Tierney LM Jr, McPhee SJ, Papadakis MA (eds): Current Medical Diagnosis and Treatment. 35th edition. Stamford, Appleton & Lange, 1996, p 260.

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10. Churg A, Colby TV, Cagle P, et al. The separation of benign and malignant mesothelial proliferations. Am J Surg Pathol 2000;24:1183-1200.

11. Aoki J, Watanabe H, Shinozaki T, et al. FDG-PET for preoperative differential diagnosis between benign and malignant soft tissue masses. Skeletal Radiol 2003;32:133-138.

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13. Ruiz-Hernandez G, de Juan R, Samanes A, et al. Tomografia por emision de positrones mediante PET-18FDG en lesiones pulmonares radiologicamente indeterminadas (positron emission tomography with [(18)F]FDG-PET in radiologically indeterminate pulmonary lesions). An Med Interna (Madrid) 2004;21:12-16.

14. Schaffler GJ, Wolf G, Schoellnast H, et al. Non-small cell lung cancer: evaluation of pleural abnormalities on CT scans with (18)F FDG PET. Radiology 2004;231:858-865.

15. Roberts PF, Follette DM, von Haag D, et al. Factors associated with false-positive staging of lung cancer by positron emission tomography. Ann Thorac Surg 2000;70:1154-1160.

16. Alexander M. FDG PET: a crucial component of initial evaluation of patients with solitary pulmonary masses [abstract]. South Med J 2002;95:S38.

RELATED ARTICLE: Key Points

* The differential diagnosis of a solitary chest mass in senior citizens includes benign and malignant mesothelioma, metastatic tumor, schwannoma, neurofibroma, lipoma, hematoma, mesothelial cyst, empyema, and effusion.

* Positron emission tomography with fluorodeoxyglucose F 18 is a noninvasive technique to stage non-small cell carcinomas of the lung, determine the malignant potential of solitary pulmonary nodules, and is a crucial component of the initial evaluation of patients with solitary pulmonary masses.

* The glycolytic activity of masses can be assessed by means of positron emission tomography with fluorodeoxyglucose F 18 to estimate the likelihood of the presence of a malignant process.

Mohab Alexander, MD, Stephen Yang, MD, Rex Yung, MD, James Robert Brasic, MD, MPH, and Harpreet Pannu, MD

From the Russell H. Morgan Department of Radiology and Radiological Science and Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD.

The authors have no commercial or proprietary interest in any drug, device, or equipment mentioned in this article.

Reprint requests to Dr. Mohab Alexander, Division of Nuclear Medicine, Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Outpatient Center, 601 North Caroline Street, Room 3245, Baltimore, MD 21287. Email: [e-mail]