TOC | Pulm
Solitary pulmonary nodule (SPN)
In general, the term SPN is reserved for nodules less than or equal to 4 cm in diameter, completely surrounded by aerated lung tissue without associated pleural effusion, atelectasis, or mediastinal adenopathy.
Over 80% of cases are equally split between bronchogenic carcinoma and granulomas.
The remaining 20% include carcinoid tumors, hamartomas, pulmonary infarcts, metastases from extrathoracic primaries, rheumatoid nodules, pulmonary dirofilariasis, vascular malformations, and a host of other less common entities (1,2).
Differentiating benign from malignant lesions is central to the evaluation of the SPN because the prognosis and role of surgery is very different for early stage bronchogenic carcinoma and granulomas.
Most patients with SPN are discovered incidentally when a chest radiograph is obtained for other reasons (health survey, preoperative evaluation, UGI scout film, etc.). By definition, the lesions are in the lung periphery and therefore rarely present with hemoptysis or signs of infection. Systemic symptoms are equally rare; the presence of significant weight loss or other "B" symptoms should prompt a search for an extrathoracic primary malignancy or associated systemic illness.
Chest x-ray & CT scan features suggesting a benign lesion include smooth borders on a symmetric spherical nodule. Lobulation, spiculation, and satellite lesions all suggest an increased likelihood of malignancy (1,3). The presence of central fat is pathognomonic of a benign pulmonary hamartoma. The presence of dense central or diffuse calcification is characteristic of a granuloma often from old fungal infection. Eccentric, stippled, or irregular calcium deposits are indeterminate in differentiating benign from malignant nodules. CT scanning also allows for the radiographic examination of the mediastinum, liver, and adrenal glands to stage the patient for possible future surgical procedures.
In small trials PET scanning appears promising, with reported sensitivities of 95-100% and specificities of 80-90% (3).
In the absence of physical examination abnormalities or unusual findings on screening laboratories, there is no role for other studies such as bone scans, liver/spleen scans, or CNS imaging techniques until the nodule has been determined to be malignant.
In most cases, if the nodule is malignant or the biopsy can not exclude malignancy, the patient will undergo diagnostic operative biopsy with attempts at curative pulmonary resection when appropriate ("when in doubt, cut it out").
The role of flexible fiberoptic bronchoscopy (FOB) in the evaluation of SPN remains controversial. The yield of FOB is related to the size of the nodule and may be as low as 10 - 20% for malignant lesions less than 2 cm in diameter. The yield for benign lesions may be even lower. Thus, a nondiagnostic FOB biopsy should not alter plans to proceed with resection. The use of fluoroscopic guidance for transbronchial biopsies and brushings may improve the yield; the addition of segmental bronchoalveolar lavage has also been stated to increase the diagnostic yield for malignant nodules.
Transthoracic needle biopsy (TTNB) of SPN will provide a positive diagnosis in malignant nodules 75-95% of the time. A false negative rate of 5-25% demonstrates that a nondiagnostic aspirate should not create a false sense of security that the lesion is benign.
Video-assisted thorocoscopic surgery (VATS) has evolved as an additional approach to the diagnosis/treatment of SPN (4). In this technique, the thorax is entered at multiple sites through small incisions using a videoscope to localize the lobe of interest. The lung containing the nodule is then biopsied with a wedge resection stapler. If frozen section evaluation reveals a neoplasm the incisions can be extended and formal cancer surgery performed. If the nodule is benign, then the patient is spared a full thoracotomy.
Approach to the SPN
There is at present no general consensus on how to optimally manage the patient with an SPN. Most authors agree that demonstrating a benign pattern of calcification on chest x-ray or retrospectively demonstrating no nodule growth over at least 2 years are solid signs that an SPN is benign, and no further evaluation is necessary. Likewise, a new nodule of greater than 3 cm in a high risk patient should be considered malignant and resected if possible.
1. Lillington, G.A. and C.I. Caskey. Evaluation and management of solitary and multiple pulomnary nodules. Clinics in Chest Medicine. 1993; 14(1):111-119
2. Swensen, S.J., J.R. Jett, W.S. Payne, R.W. Viggiano, P.C. Pairolero, and V.F. Trastek. An integrated approach to evaluation of the solitary pulmonary nodule. Mayo Clinic Proceedings 1990;173-186.
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