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* In radiologic evaluation and gross exam, This tumor diffusely involved pleural surface, making diffuse pleural thickening and pleural effusion. There is no definitive parenchymal mass except for directly extended foci from pleural mass.

*Histologic Findings of this tumor
 - Solid sheets or nests of large pleomorphic epithelioid cells
 - Small amount of fibrocollagenous stroma
 - Slitlike or cystlike spaces, Anastomosing channels
 - Cystic spaces lined by papillary or micropapillary tumor projections
 - Large round to oval pleomorphic nuclei with prominent nucleoli
 - Intracytoplasmic vacuoles or lumen
 - High mitotic and apoptotic figures
 - Confluent necrosis

*Above histologic findings are highly suggestive of malignant mesothelioma and typical features of malignat mesothelioma. Gross findings are fully supportive. I diagnosed this tumor as malignant mesothelioma at first glance, and performed several immunohistochemical markers for confirmation (cytokeratin, vimentin and calretinin). If these markers are positive, I make a diagnosis of malignant mesothelioma. ^^

*But, tumor cells showed no immunoreactivity for cytokeratin and calretinin. After then, I search out differential diagnosis for this tumor as following.

*Differential Diagnosis

• - Epithelioid angiosarcoma
 - Epithelioid hemangioendothelioma
 - Epithelioid mesothelioma

• - Pseudomesotheliomatous carcinoma

• - Metastatic adenocarcinoma

* mesothelioma, carcinoma and metastatic carcinoma were already ruled out, because
cytokeratin and calretinin immunostainig were negative.

*Notably, we have to know that vascular tumors have closely similar histologic features of mesothelioma. The only histologic differential point is intracytoplasmic vaculoe and lumen which is containing degenerative red blood cells, in addition to vasoformative growth pattern. Immunohistochemical study should be required.

*Finally, this tumor showed immunoreactivity for vascular markers (CD34, CD31).
Highly anaplastic, epithelioid tumor cell morphology, necrosis and active mitosis suggest a epithelioid angiosarcoma rather than hemangioendothelioma.

*In addition, I can find basal lamina around the rumor cell and Weibel-Palade bodies in the cytoplasm on electron microscopic examination.

 

***Primary Angiosarcoma of the Pleura

•
- Extremely rare in the pleura

•- Age: 22~79 yrs (mean: 57 yrs)

•- Male predominance
- Cause: Tuberculous pyothorax, previous irradiation, asbestos exposure

••- Clinical presentation: Diffuse pleural thickening and effusion
  --> Clinically and radiologically prompting the diagnosis of mesothelioma in most cases

•- Regional lymph node metastasis

–  --> Angiosarcoma: 5/46 (10.9%)  cf. 3.4% of all soft tissue sarcoma

•- Prognosis: Fatal

– --> Patients died few months after diagnosis of angiosarcoma

***Differential Diagnosis

- Immunohistochemistry

–  - Mesothelial markers (calretinin, hBME, cytokeratin)

–  - Epithelial marker (cytokeratin, TTF-1)

•    -- All mesotheliomas and adenocarcinomas are strongly positive for cytokeratin

•    -- Cytokeratin may be weakly positive in the epithelioid type of angiosarcoma

–  - Endothelial cell markers (CD31, CD34, Factor VIII, vWF, Ulex Europaeus)

•    -- When mesothelial and epithelial marker is negative or focal, weakly positive

•    -- Vascular marker panel should be applied

•
  - Electron microscopy

–    -- Adenocarcinoma: microvilli

–    -- Mesothelioma: microvilli (long, narrow and slender)

–     -- Vascular tumor (basal lamina around the cell border, lumen formation, Weibel-Palade body)

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