A multilocular thymic cyst associated with mediastinal seminoma: evidence for its medullary epithelial origin highlighted by POU2F3-positive thymic tuft cells and concomitant myoid cell proliferation.

Multilocular thymic cyst (MTC) and germ cell tumors are common diseases that impact the mediastinum. Correctly diagnosing these diseases can be difficult because several other conditions can mimic them. We report a male patient with MTC associated with mediastinal seminoma. A needle biopsy of the mediastinal tumor revealed numerous epithelioid cell granulomas that mimicked sarcoidosis or mycobacterial infection. However, large atypical cells positive for Oct3/4 and KIT were noted between the granulomas; thus, we diagnosed the patient with mediastinal seminoma. The resected tumor, after chemotherapy, consisted of multiple cystic lesions, and a residual germ cell tumor was first considered. However, thymic medulla-specific elements, namely, POU2F3-positive thymic tuft cells and rhabdomyomatous myoid cells accompanying the epithelium, led to the correct diagnosis of MTC. Our case underscores the importance of recognizing the histological features associated with mediastinal seminoma and provides novel findings for MTC pathogenesis, namely, the presence of thymic tuft cells.

Thymic adenocarcinoma associated with thymic cyst: a case report and review of literature.

Thymic adenocarcinoma of the mediastinum is extremely rare. Only 12 cases adenocarcinoma associated with a thymic cyst have been reported in the literature. In this report, we describe a case of a thymic adenocarcinoma associated with thymic cyst. A 70-year-old man, presented with two months of chest tightness, breath shortness and chest pain. The contrast enhanced CT scan of chest revealed a round, cystic mass in right anterior mediastinum. Microscopic examination revealed that the lining consisted of flat to cuboidal and columnar epithelium and adenocarcinoma infiltrated into the thymic tissue and the soft tissue around the wall of cyst. Based on clinical history, imaging studies, pathological findings and absence of extramediastinal tumor, a diagnosis of thymic adenocarcinoma associated with thymic cyst was established. The patient was alive without any sign of recurrence 7 months after the operation.

A case of coelomic cysts of the mediastinum.

Coelomic cysts are rare cysts of mesothelial origin. They are generally unilocular and can develop in various sites. We describe a case of a multicystic lesion discovered incidentally in the anterior mediastinum of a 41-year-old man. Immunohistochemistry confirmed multiple coelomic cysts of the mediastinum.

Multilocular thymic cyst associated with thymoma: a clinicopathologic study of 20 cases with an emphasis on the pathogenesis of cyst formation.

Multilocular thymic cysts (MTCs) are considered to be acquired lesions associated with various inflammatory conditions and/or malignant tumors. MTCs associated with thymomas are rare, with only 11 cases having been reported. On reviewing 110 consecutive patients with thymomas, we found 20 cases of MTCs. The patients included 18 men and 2 women aged 32 to 65 years (median 52 y). Eleven of the patients were symptomatic, and 6 presented with symptoms associated with inflammation. Computed tomography images were available for 11 patients, and cystic lesions were identified in 4 patients. The histologic subtypes of thymoma observed were: 3 tumors of type AB, 4 tumors of type B1, 9 tumors of type B2, and 4 tumors of type B3. In addition, 2 tumors were in advanced stages. Multilocular cystic structures accompanied by acute and chronic inflammation were observed in the remnant thymic tissues. Immunohistochemically, CK13 was diffusely expressed in the inner surface cells lining the cysts, whereas CK5/6 and p63 were primarily expressed in the basal cells of the cysts. D2-40 was weakly expressed in a small number of basal epithelial cells. The immunohistochemical profiles of the cysts were similar to those of Hassall corpuscles of normal thymi. A clinical follow-up showed that 15 patients continued to be alive without any evidence of disease, 1 patient with tumor recurrence continued to be alive, and 3 patients had died of other diseases. Our results suggest that MTCs associated with thymomas are not as uncommon as thought and may develop from the promotion of differentiation of increased numbers of epithelial cells into Hassall corpuscles by inflammatory processes. Our data also suggest a better clinical behavior for patients with thymomas accompanied by MTCs than patients with thymomas unaccompanied by those cysts, although further investigation is needed.

Cystic well-differentiated neuroendocrine carcinoma (carcinoid tumor): a clinicopathologic and immunohistochemical study of two cases.

Two cases of primary neuroendocrine carcinoma (carcinoid tumor) arising in the walls of a multilocular thymic cyst (MTC) are described. The patients were 2 men, ages 36 and 44 years. Clinically, the patients had chest pain, cough, and dyspnea. Radiographic evaluation demonstrated the presence of anterior mediastinal tumor in both patients, and complete surgical resection of the tumor mass was performed. The tumors measured approximately 6 and 8 cm in greatest dimension and were cystic with solid areas but did not show areas of necrosis or hemorrhage. Histologic examination revealed a cystic tumor with features similar to those previously described for MTCs. In addition, in the walls of the cystic structures, there was cellular proliferation arranged in a nesting growth pattern, similar to the more solid areas of the tumor. The tumor was characterized by a homogenous cellular proliferation with mild cellular atypia and no more than 2 mitotic figures per 10 high-power fields. Immunohistochemically, the tumor cells showed strong positive reactions for keratin and neuroendocrine markers, ie, chromogranin and synaptophysin. Both patients were alive after periods of 12 and 18 months.

A pancreatic cyst of the anterior mediastinum.

Although heterotopia of pancreatic tissue is a developmental anomaly found in approximately 2% of all autopsies, pancreatic tissue within the thorax and mediastinum is uncommon. In most of these instances, the pancreatic acini and islets are components of gastroenteric duplication cysts, intralobar pulmonary sequestrations, or teratomas. We describe the clinicopathologic features and hormonal profile of a patient with an anterior mediastinal cyst formed entirely by pancreatic tissue. To our knowledge, the English literature reveals only two previous examples of this lesion. The patient, a previously healthy 16-year-old girl, was found to have a cystic lesion in the anterior mediastinum during investigation of an asymptomatic heart murmur. The lesion measured 12 cm in maximal diameter and contained dark, turbid fluid. The wall was fibrotic and contained a haphazard mixture of ducts, exocrine acini, and islets. In many areas, the ducts and islets formed ductuloinsular complexes resembling those seen in diffuse nesidioblastosis. Immunohistochemical examination showed that the islets contained an increased number of B and PP cells, recapitulating the hormonal profile of the ventral anlage of the fetal pancreas. The similarity between this lesion and a fetal pancreas was further supported by the presence of a significant number of islet cells containing gastrin. The histogenesis of this lesion is unclear; we think that this lesion represents a derivative of the ventral (anterior) primitive foregut, but unidirectional differentiation of a benign cystic teratoma cannot be excluded.