Based on its location, carcinoid of the lung is classified into bronchial (central) and parenchymal (peripheral or intrapulmonary) tumors. Among bronchial carcinoids, tumors that predominantly develop within the lung parenchyma and have only a small intrabronchial component are referred to as iceberg tumors.1,2 We present a patient with an iceberg tumor in whom computed tomography images were available from several years previously. Serial computed tomography allowed us to observe the progression of this iceberg carcinoid tumor originating in the lung parenchyma and later extending into the bronchial lumen.
A nodular lesion was discovered in a 45-year-old man during health screening. At the age of 43 years, right upper lobe pneumonia was diagnosed at another hospital. The patient was a 24 pack-year smoker, but had no respiratory symptoms and auscultation revealed no abnormal breath sounds. Laboratory tests did not demonstrate any specific abnormalities, and the serum levels of progastrin-releasing peptide and neuron-specific enolase were within normal limits.
A plain chest radiograph showed a 1.8-cm nodular lesion in the hilar area of the right upper lobe. Unenhanced computed tomography of the chest (Fig. 1) demonstrated an endobronchial tumor in the right upper apical segmental bronchus (B1), which almost completely obstructed the bronchus. The endobronchial part of the tumor was continuous with the extraluminal lung parenchyma, whereas the extrabronchial part of the tumor was situated between the right upper apical subsegmental bronchi (B1a and B1b). Bronchoscopy revealed a polypoid tumor with a smooth glossy surface in the right upper apical segmental bronchus (Fig. 2). Endobronchial biopsy led to a pathologic diagnosis of typical carcinoid. Accordingly, we diagnosed this case as bronchial carcinoid originating from a central bronchus. The clinical stage was T1N0M0, so right upper lobectomy was performed.
When the resected tumor tissue was examined under a low-power microscope (Fig. 3), the mass was found to be substantially extrabronchial and intraparenchymal with partial protrusion into the lumen of the right upper apical segmental bronchus (B1). The tumor had a clear border and grew in an exophytic fashion, compressing the surrounding lung tissue. These findings corresponded to the features of an iceberg tumor. At higher magnification, light microscopy showed that the tumor featured nests of cells and a rosette-like growth pattern, and the tumor cells had uniform cytologic features with moderately eosinophilic, finely granular cytoplasm and fine granular nuclear chromatin. Necrosis and mitotic figures were absent. Immunohistochemical staining for chromogranin was positive.
We requested imaging data from the hospital where the patient was diagnosed with pneumonia 2 years previously (Fig. 4). Unenhanced computed tomography images from that time showed a tumor with a diameter of 11 mm in the extrabronchial space between the right upper apical subsegmental bronchi (B1a and B1b). The tumor was attached to the right upper apical subsegmental bronchi (B1a and B1b), but the lumen of the right upper apical segmental bronchus (B1) was intact. These findings suggested that the patient's tumor originated from the peripheral lung parenchyma. The tumor doubling time was calculated to be 570 days.
In the variant of carcinoid called iceberg tumor, growth predominantly occurs in the lung parenchyma rather than in the bronchus.1,2 Several studies have shown that bronchial carcinoids originate from the bronchial wall,1-6 and eventually destroy the bronchial cartilage to expand outward from the bronchus during growth, finally developing into iceberg tumors. Although the term “iceberg tumor” is mentioned in Fraser's textbook,1 the mechanism of growth has not been sufficiently elucidated.2-6 Among 13 patients with typical bronchial carcinoid treated at our department, only 1 had a tumor that was entirely confined within the bronchial wall, and all of the other tumors involved both the bronchus and the lung parenchyma. In 12 patients, tumors that were predominantly located within the bronchus had a mean diameter of 11.3 mm, whereas iceberg tumors (predominantly within the lung parenchyma) had a mean diameter of 26.5 mm. These data also support a mechanism in which carcinoid originates in the bronchial wall and later grows into an iceberg tumor.1
In the present patient, we were able to review the computed tomography findings from 2 years previously, and we thus demonstrated that the carcinoid was completely localized within the extrabronchial space with no endobronchial component 2 years earlier. Changes on successive computed tomography images suggested that the endobronchial polyp formed later, thus completely contradicting the existing concept about the mechanism of iceberg tumors. The imaging findings obtained in the present patient suggest the possibility that some iceberg tumors form by the invasion of a peripheral carcinoid into the bronchial wall. There have only been a few reports on iceberg tumors, and further research into the patterns of growth is necessary. Bronchoscopists should pay careful attention during the diagnosis of bronchial carcinoid.
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4th ed. Philadelphia: WB Saunders; 1999:1229-1250.
2. Ishida T, Yokoyama H, Sugio K, et al. Carcinoid tumor of the lung: clinicopathological and immunohistochemical studies. Eur J Surg Oncol
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4. Colby TV, Koss MN, Travis WD. Carcinoid and other neuroendocrine tumors. In: Rosai J, Sobin LH, eds. Atlas of Tumor Pathology. Tumors of the Lower Respiratory Tract
. Washington, DC: AFIP; 1995:287-318.
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6. Fink G, Krelbaum T, Yellin A, et al. Pulmonary carcinoid-presentation, diagnosis, and outcome in 142 cases in Israel and review of 640 cases from the literature. Chest