Radiographic Findings

A frontal chest radiograph shows a mildly lobular, well-defined mass, 3.5 cm in diameter, localized on the lateral film (not shown) in the suprahilar region of the right upper lobe.

Differential diagnosis: The differential diagnosis of a pulmonary nodule or mass has been discussed in cases 1, 2, and 4. Since the patient initially refused work-up of his mass, this case provides an opportunity to consider the significance of nodule growth rate. Nodule growth is usually expressed as the time in which the volume doubles, i.e., "doubling time." It is calculated by using the equation 4/3 pi r3. As an estimate, a 26% increase in diameter indicates one doubling of volume.

In 1991, the nodule in this case measured 2.5 cm in diameter. One doubling of volume equals a diameter of 3.15 cm and two doublings would be 4 cm. Therefore, four years later in 1995, the mass (then 3.5 cm in diameter) had doubled less than twice, which gives a doubling time of over 2 years.

Most bronchogenic carcinomas have a doubling time between 1 and 18 months [1]. Slowly-growing nodules are more commonly benign [2]. Etiologic considerations for a slowly-growing lung nodule include hamartoma, bronchial carcinoid, inflammatory pseudotumor, granuloma, and, uncommonly, slowly-growing primary carcinoma (especially adenocarcinoma) or metastasis from renal cell carcinoma [3]. Nodules that show stability in size for at least 2 years are generally considered benign [3]. However, increase in nodule size, even slow growth, usually warrants further evaluation because malignant neoplasms, including carcinoid tumors, may grow slowly. Unless CT findings, such as the presence of fat and calcium for hamartoma [4], are characteristic for a benign etiology, biopsy or excision is usually necessary.

CT at level of nodule: A sharply-defined, mildly lobular mass is present in the suprahilar region of the right upper lobe. Increased lucency of part of the anterior segment of the right upper lobe suggests obstructive vasoconstriction and/or hyperinflation secondary to mass-effect on a subsegmental bronchus.

References

1. Garland L, Coulson W, Wollin E. The rate of growth and apparent duration of untreated primary bronchial carcinoma. Cancer 1963; 16:694-707.

2. Madewell J, Feigin D. Benign tumors of the lung. Semin Roentgenol 1977; 12:175-185.

3. Reed J. Chest Radiology Plain Film Patterns and Differential Diagnoses, 4th ed. St. Louis, Mosby-Year Book, 1997, p 341.

4. Siegelman S, Khouri N, Scott W, et al. Pulmonary hamartoma: CT findings. Radiology 1986; 160:313-317.

Clinical Summary Image 1

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