AIM: This article reviews the literature on the clinical features, diagnosis and management of primary intrapulmonary thymoma. METHODS: Medline, Embase and Cochrane Library searches were performed on all relevant Anglo-Saxon language articles. The search words included "primary pulmonary thymoma" and "intrapulmonary thymoma". Secondary references were obtained from key articles. Prognostic and treatment strategies were analyzed by the Kaplan-Meier method, comparisons between curves were made using log rank test. RESULTS: The searches yielded 25 cases of primary intrapulmonary thymoma. Median follow-up was 9 months (1 day to 13 years). At follow-up, 14 patients were tumor free, one patient had a local recurrence 8 years after radiotherapy, one patient responded favorably to radiotherapy, six patients died and three patients were lost to follow-up. The presence of a paraneoplastic syndrome decreased survival (P=0.02), however, histological subgroup (P=0.216), clinical stage (P=0.63) and tumor size (P=0.288) did not affect survival. Survival in surgically managed patients was significantly better than in conservatively managed patients (P=0.039). Adjuvant radiotherapy did not provide any benefit (P=0.4). CONCLUSION: Complete resection of primary intrapulmonary thymomas appears sufficient in non-malignant tumors. Because of the risk of late local recurrence, long-term regular clinical follow-up is warranted.

Primary intrapulmonary spindle cell thymoma with marked granulomatous reaction: report of a case with review of literature. Int J Surg Pathol. 2003 Oct;11(4):353-6.

Primary intrapulmonary thymoma is a rare lesion with around 20 cases reported so far in the literature. A pure spindle cell morphology in these lesions is rarer still with only a single case recorded to date. We report herein an interesting case of a 47-year-old-man, status post surgical resection and radiotherapy for a squamous cell carcinoma of the floor of mouth, who was being followed up for a radiologic opacity in the right lower lobe of the lung. The lesion remained stable in size for almost 5 years and then an increase in size was noted. A right lower lobectomy was performed with a preoperative suspicion of metastasis. Histologic and immunohistochemical evaluation revealed a primary intrapulmonary spindle cell thymoma that displayed a prominent granulomatous reaction, a phenomenon not described so far in the literature. We discuss the possible embryologic origins and the pitfalls in diagnosis of these rare neoplasms. The remarkable granulomatous response observed in the tumor raises the possibility that similar lesions might conceivably occur in the thymus as well.

Primary intrapulmonary thymoma successfully resected with vascular reconstruction. Ann Thorac Surg. 2003 Nov;76(5):1735-7.

Primary intrapulmonary thymomas are defined as intrapulmonary tumors without an associated mediastinal component and are very rare. We report a resected case of primary intrapulmonary thymoma with dissection of mediastinal lymph nodes and vascular reconstruction. Because the tumor directly invaded the right brachiocephalic vein, the vein was reconstructed with a graft, and then adjuvant radiation was performed postoperatively. The tumor was diagnosed as a lymphocyte dominant thymoma and B2 type thymoma in the WHO classification. There has been no evidence of recurrence in 6 years. Complete resection of the tumor with vascular reconstruction and adjuvant radiation should be considered in invasive intrapulmonary thymoma.

A case of primary intrapulmonary thymoma: its entity and the problem of lymph node dissection. Kyobu Geka. 2000 May;53(5):369-74.

Primary intrapulmonary thymomas are defined as primary thymomas arising in an intrapulmonary location without an associated mediastinal component, and they are very rare. A total of 20 cases have been reported only sporadically in the English literature since 1951. We reported the case of 41-year-old woman who had a 3.5 x 3.0 x 3.0 cm lower right lobe mass with nodal metastasis that extended over the left atrium. We also summarized the clinicopathological features of a total of 21 cases and discussed the problems involved with diagnosis, pathogenesis and treatment. Knowledge of the biological behavior of primary intrapulmonary thymomas is limited because of their rarity. In particular, the issue of the need for lymph node dissection has not been adequately discussed. In this case, pathohistological examination revealed that the routes of lymphatic spread and the sites of nodal metastases from primary intrapulmonary thymoma resemble those of primary lung cancer. Therefore, systematic mediastinal lymph node dissection according to the lymph node map for primary lung cancer should be recommended for malignant cases.

Primary pulmonary thymoma.Ann Thorac Surg. 1997 Nov;64(5):1471-3.

Primary thymomas arising in an intrapulmonary location without an associated mediastinal component are rare entities. The origin of thymomas in this unusual location remains unknown. Knowledge of the natural history and the prognosis of these tumors is also limited because of their rarity.

Primary intrapulmonary thymoma. A clinicopathologic and immuno-histochemical study of eight cases. Am J Surg Pathol.1995 Mar;19(3):304-12.

We describe eight cases of primary intrapulmonary thymoma occurring in seven women and one man between the ages of 25 and 77 years. Clinically, all patients had initial radiographic findings of a parenchymatous intrapulmonary mass without evidence of mediastinal involvement either radiologically or at surgery. The lesions varied from 0.5 to 10 cm in greatest diameter. Five tumors were located close to the hilum, while the other three were discovered deep within the lung and in subpleural locations. In one case, the lesion appeared to arise endobronchially and infiltrate the surrounding parenchyma. In another case, in addition to the main hilar mass, there were two smaller tumor nodules found deep within the same lung. Histologically, the lesions were characterized by the classic biphasic cellular composition of thymomas, i.e., an admixture in varying proportions of epithelial cells and lymphocytes. Four cases were characterized by sheets of lymphocytes admixed with scattered epithelial cells that were separated by fibrous bands into lobules. Three cases were composed predominantly of sheets of epithelial cells admixed with scattered small lymphocytes and containing prominent perivascular spaces. In two of these cases, focal areas of spindling of the cells were noted. One case was composed predominantly of a spindle cell proliferation with perivascular spaces and numerous small lymphocytes. Immunohistochemical stains for keratin and epithelial membrane antigen in six cases highlighted the epithelial cells scattered against the lymphoid cell background. Seven patients were treated by surgery. In one patient the tumor was deemed inoperable at the time of exploration owing to extensive pleural infiltration and was treated by postoperative radiation; the lesion recurred locally in the pleura 8 years later. Clinical follow-up in three patients after surgical incision showed them to be alive and well without evidence of disease at 10 months, 2 years, and 8 years, respectively. Two of the patients had been followed clinically for 2 and 4 years following discovery of their lung masses on routine chest radiograph before resection of their tumors. Two patients died of unrelated conditions; in one of them, the lesions had been followed clinically for 6 years before surgery; this patient died 6 months later from coronary artery disease, without evidence of recurrence or metastasis. Our findings suggest that intrapulmonary thymomas are slow-growing tumors that may respond well to surgical resection when confined to the lung. As with their mediastinal counterparts, invasive tumors will require additional treatment for the possibility of recurrence of metastasis.

Pulmonary and pleural thymoma. Diagnostic application of lymphocyte markers to the thymoma of unusual site. Am J Clin Pathol. 1988 May;89(5):617-21.

Two cases of the thymoma of the unusual sites were examined immunohistochemically. The one was intrapulmonary, and the other was diffuse pleural tumors. The infiltrating lymphocytes were T-cells showing OKT 6 positivity and nuclear immunoreactivity for terminal deoxynucleotidyl transferase (TdT) in the intrapulmonary tumor, like lymphocytes in the mediastinal thymoma of predominantly lymphocytic or mixed types. Although lymphocytes were dispersed in the pleural tumor, there were some TdT(+) OKT 6(-) lymphocytes and the similar finding was observed in the thymoma of predominantly epithelial type. In lung carcinomas and pleural mesotheliomas, there were no TdT(+) OKT 6(+/-) lymphocytes. Immunohistochemical studies using lymphocyte markers may be an useful tool for the diagnosis of the thymoma of ectopic site or unusual presentation.

Intrapulmonary thymoma. Arch Pathol Lab Med. 1987 Nov;111(11):1074-6.

A 50-year-old man presented with a lung mass in the left upper lobe, which was shown by electron microscopy to be a thymoma. There was no evidence of a mediastinal mass. The lymphocytes of the tumor reacted with monoclonal antibody T101, a pan T-cell marker, and with OKT8. B1 and B2 surface antigens characteristic of B lymphocytes were not detected. Tumors of thymic epithelial cells completely covered by pleura without mediastinal involvement are rare.

Intrapulmonary thymoma. Thoraxchir Vask Chir. 1975 Feb;23(1):14-20.

A primary intrapulmonary left-sided thymoma is described in a 23-year old man. Eight similar observations can be found in the world literature. The histology is quite uniform. The tissue shows characteristic epithelial and lymphatic cellular elements but organoid differentiation into medullar and cortex is lacking. Hassall's granules are only rudimentary. Giant cells in all stages of development, tissue mast cells, varied supporting tissue, epithelial border layer and connective tissue capsule are all present. There is no blastomatous degeneration. Theoretical indications to explain the sudden onset of tendency to proliferation of the ectopic thymus independant of age and sex are discussed.

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