Epithelioid hemangioendothelioma of the anterior mediastinum. Clinicopathologic, immunohistochemical, and ultrastructural analysis of 12 cases

Composite hemangioendothelioma: a complex, low-grade vascular lesion mimicking angiosarcoma

Eight cases of a previously uncharacterized vascular neoplasm, showing varying combinations of benign, low-grade malignant, and malignant vascular components are described. Seven tumors occurred in the dermis and/or subcutis and one occurred in the oral submucosa. The patients were all adults with a median age of 39.5 years (range, 21-71 years). Five patients were men. The tumors arose predominantly in the hands and feet, and the lesions were usually of several years duration. The tumors were composed of a complex admixture of histologic components that varied from tumor to tumor, such that no two tumors looked precisely the same. This was due to variation in the proportions of each component as well as the manner in which each component was distributed throughout each lesion. The predominant histologic components were epithelioid hemangioendothelioma (HE) and retiform HE, which were each present in seven of the tumors. Areas of spindle cell HE were identified in four lesions. Angiosarcoma-like elements were identified in seven tumors. One of the tumors was associated with an arteriovenous malformation and one was associated with an area of lymphangioma circumscriptum. Of six cases with follow up (median duration, 6.5 years), three have recurred locally and, to date, only one has metastasized. We think composite HE is best regarded as a low-grade malignant vascular neoplasm, and the available data suggest that it behaves more favorably than conventional angiosarcoma. The existence of these composite lesions has led to careful reexamination of the concept of HE. The term HE, in that it is currently synonymous with a low-grade malignant vascular tumor, should be reserved for lesions that have true metastatic potential, albeit with low frequency.

Epithelioid Hemangioendothelioma of the Spermatic Cord

This report describes an epithelioid hemangioendothelioma arising on the spermatic cord of a 50-year-old man who presented with a nodule in the right hemiscrotum. Histologic examination showed a cellular tumor composed of epithelioid cells, many of which had intracytoplasmic lumina containing red blood cells. Immunohistochemistry showed focal positivity of tumor cells with the endothelial markers CD34, factor VIII-related antigen, and Ulex and with the anticytokeratin antibodies CAM5.2 and AE1/AE3. Ultrastructural examination revealed polygonal tumor cells forming vascular spaces and intracytoplasmic lumina containing red blood cells. This is the second documented occurrence of epithelioid hemangioendothelioma at this site. The case illustrates the value of immunohistochemistry and electron microscopy in establishing a diagnosis. Int J Surg Pathol 8(1):75-78, 2000

Aggressive epithelioid hemangioendothelioma of the lower extremity: a case report and review of the literature

A case of epithelioid hemangioendothelioma (EHE) of the left lower extremity in a 50-year-old male is discussed. The neoplasm presented as a tan-purple, painful mass involving the fourth digit of the left foot. Following an excisional biopsy and partial amputation of the fourth digit, the lesion recurred with a multifocal distribution. A physical exam following the recurrence demonstrated multiple palpable lymph nodes in the left inguinal region. A complete amputation of the fourth digit was performed in conjunction with local excisions of the remaining lesions. Additionally, an inguinal lymphadenectomy was performed for staging purposes. Histologically, the tumor was predominantly composed of epithelioid endothelial cells forming nests, cords, and sheets and occasionally forming irregular, primitive vascular structures. Less commonly, nests of tumor cells assumed a spindled morphology. Patches of necrosis and hemorrhage were apparent throughout the neoplasm. There was minimal atypia and mitoses were not identified. Immunohistochemical stains for CD34, CD31, and Ulex europaeus antigens were positive in tumor cells. This case illustrates the potential aggressive behavior of this rare neoplasm and argues against the designation "tumor of low-grade malignancy" with which it is commonly attributed.

Epithelioid hemangioendothelioma of the liver: a clinicopathologic study of 137 cases

BACKGROUND

Epithelioid hemangioendothelioma (EHE) is a rare neoplasm of vascular origin that occurs in the liver and other organs; its etiology is unknown.

METHODS

The authors analyzed the clinicopathologic and immunohistochemical features of 137 patients with EHE of the liver in an attempt to identify features that might predict tumor behavior. To their knowledge, this article represents the largest series reported from one institution.

RESULTS

Patients were ages 12-86 years; 84 (61%) were females and 53 (39%) were males. They presented with nonspecific symptoms such as right upper quadrant pain or weight loss. Macroscopically, the tumors usually were multiple. They typically were white, firm to hard, and ranged in size from 0.2-14 cm. Histologically, the tumors were comprised of dendritic and epithelioid cells that often contained vacuoles representing intracellular lumina. The stroma was fibrous, with myxohyaline areas. Immunohistochemically, all tumors were positive for at least one endothelial marker (factor VIII-related antigen [FVIII-RAg], CD34, and/or CD31). Treatment modalities included hepatic resection or transplantation. Although the metastatic rate in this series was 27%, the prognosis is considered much more favorable than that of other hepatic malignancies. Twenty-six patients (43%) survived > or = 5 years; 2 patients were alive and well at last follow-up after 23 and 27 years, respectively. Twenty-six of 60 patients (43%) died of their disease, 1 of whom died 28 years after discovery of her tumor. In an attempt to predict behavior of the tumor, several histologic parameters were evaluated using univariate analysis. No significant correlation was found with mitoses, Glisson's capsule infiltration, or nuclear atypia. High cellularity was significantly correlated with a poor clinical outcome (P = 0.00012), whereas the association with tumor necrosis approached significance (P = 0.057).

CONCLUSIONS

EHE is a very rare clinical entity. The key to diagnosis is the demonstration of cells containing FVIII-RAg. The histology of the tumor, including nuclear pleomorphism and the mitotic count, are of no value in predicting clinical outcome. High cellularity most likely is the most significant parameter predicting an unfavorable prognosis in EHE because mitotic counts often are quite low in both low grade and aggressive tumors. Further studies are needed to identify the factors responsible for the apparent dissociation between the clinical behavior and biologic characteristics of this tumor.

Multiple cutaneous epithelioid hemangioendothelioma: a case with spindle cells

A case of multiple cutaneous epithelioid hemangioendothelioma (EH) in a Japanese male is reported. The patient was a 52-year-old Japanese bureaucrat. Clinically, about 10 purplish-red, elastic soft or hard papules and nodules had appeared on both lower extremities and the left buttock over the past 20 years. They were excised, but some of them recurred. Histologically, the papules and nodules were well-circumscribed tumors located in the superficial and deep dermis. They appeared to arise from medium-sized vessels and were composed of proliferations of characteristic epithelioid endothelial cells with intracytoplasmic vacuolization and spindle cells. No other extracutaneous tumors were found. We diagnosed the present case as multiple cutaneous EH with spindle cells. The presence of epithelioid endothelial cells and absence of pleomorphism and mitoses of nuclei of spindle cells made differential diagnosis from Kaposi's sarcoma possible. The protracted clinical course seems characteristic of EH in various organs including skin.

Epithelioid hemangioendothelioma of bone and soft tissue: a fine-needle aspiration biopsy study with histologic and immunohistochemical confirmation

We retrospectively reviewed two fine-needle aspiration biopsy (FNAB) specimens from two patients with histologically confirmed epithelioid hemangioendothelioma (EH). Both patients were men, ages 79 and 39 years; their primary tumors arose in the soft tissues of the mediastinum and within the proximal tibia, respectively. The former patient had symptoms of superior vena cava syndrome; multicentric intraosseous lesions involved the proximal tibia of the latter patient. All cytologic smears were hypercellular and composed of mostly disassociated single cells and small aggregates of ovoid to polygonal-shaped epithelioid cells. Nuclei were variable, ranging from ovoid and reniform to round and polylobated and surrounded by an abundant amount of dense cytoplasm. Binucleated epithelioid neoplastic cells were frequent. Nuclear pleomorphism ranged from slight to moderate, and small solitary to multiple nucleoli were identified within the majority of tumor cells. Rare neoplastic cells with a single, sharply demarcated intracytoplasmic vacuole and intranuclear cytoplasmic pseudoinclusions were observed in the smears of one tumor. Metachromatic stromal fragments, probably representing hyalinized chondromyxoid stroma, were seen in the other tumor. Neither case was recognized initially on FNAB as EH. Immunohistochemically, sections from the surgical biopsy specimens of both cases showed diffuse and strong immunopositivity for the endothelial marker CD31. Although the cytomorphology of EH appears distinct, clinicoradiologic correlation is essential, and immunohistochemistry may be helpful to avoid misdiagnoses.

Epithelioid haemangioendothelioma of the thyroid gland: a case report and review of literature

AIMS

This is a hitherto unreported case of an epithelioid haemangioendothelioma of the thyroid gland.

METHODS AND RESULTS

The patient was a 44-year-old woman who presented with a right thyroid mass. A right subtotal thyroidectomy was performed. Histologically the lesion had characteristic epithelioid and spindle cell proliferation in a background of chondromyxoid stroma. Cytoplasmic vacuolization in the epithelioid and spindle cells was present. No atypical mitotic activity or necrosis was noted. The tumour cells were positive for factor VIII-related antigen, Ulex europeus and CD 31 and were negative for cytokeratin.

CONCLUSION

The patient has been followed for 24 months and is free of recurrent and metastatic disease, which is supportive of a benign course in the thyroid gland.

Intracranial epithelioid hemangioendothelioma arising at site of previously excised atypical meningioma

Epithelioid hemangioendothelioma is an uncommon vascular tumor which, in most cases, pursues a clinical course intermediate between hemangioma and angiosarcoma. Only four completely documented cases of central nervous system involvement by this tumor appear in the literature. We present an additional case, which is remarkable in its occurrence at the site of a previously excised atypical meningioma and in its unusually aggressive clinical course. To our knowledge this is the first report of intracranial epithelioid hemangioendothelioma with postmortem documentation. The patient initially presented with a 7 cm right post frontal tumor; an atypical meningioma was excised and removal appeared complete on immediate post-operative scans. Seven months later the patient re-presented with tumor recurrence at the previous operative site; a second craniotomy was performed and, on this occasion, the excised tumor had the histological features of an epithelioid hemangioendothelioma without evidence of meningioma: both morphologically and immunohistochemically the two tumors were quite distinctive. Further recurrence prompted radiotherapy but the patient continued to deteriorate and died five months later. Massive recurrence of intracranial tumor was found at postmortem examination.

Endovascular papillary angioendothelioma (Dabska tumor) in an elderly woman

A patient with endovascular papillary angioendothelioma with a low grade of malignancy showing papillary proliferation of endothelioid cells is presented. The patient, an 83-year-old woman, underwent resection of a tumor of the neck. At operation a 9 x 7 cm cystic tumor containing yellow transparent liquid with clots was found in the subcutaneous tissue. Histological studies showed endothelioid cells with spindle-shaped nuclei proliferated in layers around the fibrovascular cores, which showed the characteristic appearance of papillary proliferation. These cells were immunohistochemically positive for CD31, CD34 and factor VIII-related antigen. Based on these observations, the tumor was considered to be an endovascular papillary angioendothelioma (Dabska tumor). Dabska tumor is a vascular tumor with a low grade of malignancy and usually occurs in infants and young children. About 13 cases of Dabska tumor have been reported. The occurrence of a Dabska tumor in an aged patient is considered to be rare.

Myxoid chondrosarcoma (chordoid sarcoma) of bone: a report of two cases and review of the literature

BACKGROUND

Chondrosarcoma of bone is a well recognized, relatively common clinicopathologic entity. Morphologically distinct soft tissue chordoid sarcoma (CS), or extraskeletal myxoid chondrosarcoma, is a relatively rare tumor that has generally been documented in extraosseous soft tissues.

METHODS

The clinical and pathologic features of two patients with biopsy-proven CS from the pathology files of the Mayo Clinic and St. Thomas's Hospital were evaluated. Routine hematoxylin and eosin-stained slides were reviewed in both cases. Sections from both were examined immunohistochemically using the avidin-biotin-peroxidase technique and employing commercially available antibodies to the following antigens: S-100 protein, cytokeratin (AE1/AE3), epithelial membrane antigen (EMA), CD31, and factor VIII. Appropriate positive and negative controls were utilized throughout these procedures. Cytogenetic analysis was performed on fresh samples obtained from one tumor. Clinical data were obtained from the patients' medical records.

RESULTS

The two cases of primary CS of bone arose from the right distal femur and right scapula, respectively, in 2 men ages 48 and 76 years, respectively. Morphologically, the tumors were lobulated, multinodular, and comprised of a uniform population of rounded to slightly spindled cells. Nuclei were hyperchromatic with inconspicuous nucleoli and surrounded by clear, vacuolated to eosinophilic cytoplasm. Neoplastic cells were arranged in anastomosing chords, strands, and, less often, nests and pseudopapillary structures embedded in an abundant, mostly hypovascular, mucinous matrix. Foci of hemorrhage and cystic degeneration were present in both tumors. No well developed hyaline cartilage or neoplastic osteoid was observed. Immunohistochemically, one neoplasm showed focal positivity for S-100 protein but was uniformly negative for cytokeratin (AE1/AE3), factor VIII, and CD31. The other tumor showed no immunopositivity with cytokeratin, EMA, or S-100 protein. Cytogenetic analysis in the latter tumor revealed a nonrandom reciprocal chromosomal translocation, t(9;22)(q22-31;q11-12). Both patients developed local recurrences and widespread distant metastases. Wide surgical excision was the primary mode of therapy. One patient died of tumor.

CONCLUSIONS

Skeletal CS is an extraordinarily rare neoplasm with a distinct morphology. Although follow-up data were limited to only four examples, including two from the literature, the clinical course appears worse than that for usual chondrosarcoma of bone. Wide surgical resection appears to represent the best mode of therapy. The role of chemotherapy and radiation therapy has not been clearly defined.

Epithelioid hemangioendothelioma of skin and soft tissues: clinicopathologic and immunohistochemical study of 30 cases

Epithelioid hemangioendothelioma of soft tissues (EHE) represents a distinct entity with an unpredictable clinical course. We analyzed the clinicopathologic and immunohistochemical features in a series of 30 patients. Patient age range was 16-74 years (median 50); 18 of 30 patients were female. Eight tumors arose in the lower and two in the upper extremities, seven on the trunk, five each in the head/ neck and anogenital regions, two in the mediastinum, and one in the abdomen. Seventeen neoplasms were located in deep soft tissues, nine were subcutaneous or perifascial, and four were dermal; size ranged from 0.4 to 10 cm; in 11 cases the tumor was > 5 cm. Tumors with an infiltrative growth pattern were more common than entirely circumscribed lesions. The tumors were composed histologically of short strands, cords, or small clusters of epithelioid, round, to slightly spindled endothelial cells that formed at least focally, intracellular lumina and were set in a frequently myxohyaline stroma. Thirteen of 30 lesions showed angiocentric growth, which was occlusive in many cases. Immunohistochemically, all cases tested were positive for at least one endothelial marker (CD31, CD34, factor VIII, Ulex europaeus), six of 23 (26%) were positive for cytokeratin, and five of 11 (45%) were positive for alpha-smooth muscle actin. Median follow-up of 36 months (range 2-96) in 24 cases showed local recurrence in three cases and systemic metastases in five cases (21%); four patients (17%) died of tumor. Although more aggressive histologic features (striking nuclear atypia in eight cases, numerous spindled cells in 10, more than two mitoses per 10 high-power fields in nine, and small, more solid angiosarcomalike foci in four cases) tended to be related to poor clinical outcome, there was no clear correlation. Two metastasizing cases showed no histologically atypical features whatever. We suggest that EHE of soft tissue is better regarded as a fully malignant, rather than borderline, vascular neoplasm, albeit the prognosis is better than in conventional angiosarcoma.

Hepatic epithelioid hemangioendothelioma: biological questions based on pattern of recurrence in an allograft and tumor immunophenotype

Epithelioid hemangioendothelioma (EHE) is best considered a vascular neoplasm of intermediate malignancy. Although usually progressive, the clinical course is highly unpredictable. The present communication describes a case of extensive recurrent hepatic EHE, limited to the liver allograft and initially manifest as an insidious seeding of individual tumor cells in areas of perivenular inflammation associated with rejection. A detailed immunophenotypic characterization of this and a small series of EHE was carried out in an effort to highlight subtle disease recurrence and to gain possible insights into tumor biology associated with this intriguing disease. In a series of five cases of hepatic EHE, CD34 (QB-END/10) was found to be more sensitive than Factor VIII (F-VIII) for recognition of the disease, similar to previous reports. The former diffusely and distinctly stained both epithelioid and dendritic tumor cells, whereas staining for the latter was focal, indistinct, and showed a high background. Although the tumor cells were negative for some markers of dendritic or macrophage maturation, such as CD1a, S100 protein, Mac 387, CD68, and LN3, there was marked infiltration of hepatic EHE by factor XIIIa + (F-XIIIa), Mac 387+, CD68+, and LN3+ macrophages and dendrocytes, most of which were interpreted as reactive. The "reactive" macrophage and dendrocyte populations were present throughout the fibrotic stroma and intermingled with the epithelioid clusters of EHE. Interestingly, a small subset of tumor cells coexpressed CD34 or F-VIII and F-XIIIa, the last of which is normally restricted to cells of the monocyte/macrophage lineage and cytokine activated microvascular endothelium in vitro. The known association of F-XIIIa+ dendrocytes with granulation tissue, repair and fibrogenesis, and the modulation of F-XIIIa and F-VIII expression by inflammatory cytokines led us to speculate that EHE lesions may derive from primitive "reticuloenothelial" cells that can differentiate along endothelial and dendritic pathways. The EHE lesions may represent a neoplastic analogue of wound healing. Thus, the variability in F-VIII staining, the strong expression of CD34, the infiltration of EHE lesions with F-XIIIa+ dendrocytes, and the coexpression of CD34 and F-XIIIa on a subset of tumor cells may have an important biological basis.

Complex translocation [7;22] identified in an epithelioid hemangioendothelioma

We describe a malignant epithelioid hemangioendothelioma arising in the back of a 45-year-old man with pulmonary and bone marrow metastases. Light microscopic and immunohistochemical features of this tumor are presented. Karyotyping revealed several clonal abnormalities: a complex unbalanced translocation [7;22] involving multiple breakpoints (confirmed by fluorescence in situ hybridization), a Robertsonian t(14;14), and loss of the Y chromosome. Monosomy for chromosome 11 was noted in a subset of the tumor cells. To our knowledge a karyotype has not been previously reported for this unusual vascular tumor.

Ossifying epithelioid hemangioendothelioma

A case of small epithelioid hemangioendothelioma encapsulated by an egg-shaped bony shell composed of newly formed mature lamellar bone is presented. A nodule measuring 10 x 5 x 5 mm was excised from inside of the right cheek muscle of a 46-year-old man. Histopathologically, the nodule consisted mainly of round-to-short spindled epithelioid cells with round nuclei and occasional cytoplasmic vacuoles associated with some foci of osseous metaplasia. Characteristically, egg shell-like lamellar bone enclosed this lesion showing well-circumscribed appearance. The main component cells were immunohistochemically stained positive for factor VIII-related antigen, CD 34, UEA-1, and vimentin, and proved to be vascular endothelial cells. The term ossifying epithelioid hemangioendothelioma is proposed for this unique lesion. This type of epithelioid hemangioendothelioma has not been previously reported to our knowledge, and differentiation from ossifying fibromyxoid tumor of soft parts is considered to be important.

Malignant vascular tumors of the serous membranes mimicking mesothelioma. A report of 14 cases

Malignant endothelial neoplasms involving the serous membranes are rare, and only a few cases have been documented. We report 14 patients with epithelioid hemangioendothelioma (EHE) or epithelioid angiosarcoma (EA) diffusely involving the pleural, peritoneal, or pericardial cavities, resulting in a picture closely resembling mesothelioma. The mean age at diagnosis was 52 (range, 34-85). The patients included two women and one man with peritoneal tumors, eight men with pleural tumors, and three men with pericardial tumors. A shared histological appearance was a diffuse sheet-like and clustered pattern of tumor growth with variable degrees of vascular differentiation. A tubulopapillary growth pattern, often seen in mesothelioma, was prominent in four cases. Nine cases showed a variable number of spindle cells, some neoplastic, others reactive, focally producing a biphasic growth pattern, further suggesting mesothelioma. Initial interpretations included mesothelioma, adenocarcinoma, and, in one case with prominent spindle-cell components, leiomyosarcoma. Immunohistochemically, strong vimentin staining and negative or weak to moderate cytokeratin staining were observed in all 14 cases. The tumor cells coexpressed at least two of the four endothelial markers used in the study (CD31, CD34, von Willebrand factor, and Ulex europaeus agglutinin-I [UEA-I)]. Detection of abortive vessel formation was facilitated by staining for collagen type IV. Markers of mesothelial, epithelial, muscular, and neuronal differentiation were all negative in the subset of cases studied. As a control group, 39 mesotheliomas and more than 60 adenocarcinomas of various origins were studied using the same antibody panel. This group revealed strong keratin staining, moderate or negative vimentin staining, and no expression of any of the endothelial-lineage markers, with the exception of positive staining for UEA-I in occasional adenocarcinomas. Clinically, these endothelial tumors were highly aggressive; 12 patients presented with disseminated disease, and most died within months of the initial presentation. These findings indicate that, although uncommon, EHE/EA should be included in the differential diagnosis of serous membrane neoplasms with histological and clinical features of malignant mesothelioma. The diagnosis of an endothelial neoplasm can be suspected by the presence of abortive vessel formation and by the strong expression of vimentin, with absent or low-level expression of cytokeratin. The demonstration of immunoreactivity for two or more endothelial-associated markers is essential in confirming the diagnosis.

Hemangioendothelioma: a rare vascular tumor in childhood and adolescence

Most vascular tumors occurring in children are benign. They are recognized by their ability to form angiomatous structures. In some instances, there is no clear-cut line between a benign vascular tumor (or angioma) and a malignant vascular tumor (or angiosarcoma). The hemangioendothelioma is a rare tumor of vascular origin, involving bone or soft tissue, and represents 1% of all vascular neoplasms. Accurate diagnosis is critical in recommending the most appropriate therapy for each patient. The aim of this paper is to give a brief review of the literature of this rare entity, particularly in childhood and adolescence.

Primary epithelioid hemangioendothelioma of the brain

Epithelioid hemangioendothelioma is an uncommon form of endothelial neoplasm, one of intermediate-grade malignancy and relatively favorable prognosis. Herein we report the third and fourth cases described in the central nervous system and compare their clinical and pathologic properties with those arising at systemic sites. Both patients presented with signs and symptoms of a mass lesion with seizures present in both cases. Imaging studies revealed well-demarcated mass lesions with surrounding edema. Gross total removal was accomplished surgically in both cases One case was partially cystic and nodular; the other was firm, focally gritty, and cartilaginous in appearance. Histologically they were identical to hemangioendotheliomas of other locales: multinodular neoplasms with regional variation in cellularity, cords and clusters of epithelioid cells with variable attempts at lumen formation, and spindled cells associated with a fibromyxoid matrix. Immunohistochemical stains confirmed the endothelial natures of the cells. These cases and those previously reported were treated with surgical excision. The few patients described have ranged in age from infants to older adults. Some patients have had residual neurologic defects, but no deaths due to tumor have been reported.

Multicentric epithelioid angiosarcoma of the bone. Pitfalls in clinical and morphological diagnosis

Epithelioid angiosarcoma of the bone represents a challenging diagnosis by bone marrow biopsy. We present a case of a multicentric high grade angiosarcoma of the bone with epithelioid features. On the basis of the clinical presentation, the radiological findings, and the appearance of loosely clustered tumor cells detected in the initial bone marrow biopsy, the main differential diagnoses considered were a poorly differentiated non-secretory multiple myeloma and metastatic carcinoma. Subsequent morphologic, immunohistochemical and electron microscopic examination of tissue samples clarified the nature of the tumor as epithelioid angiosarcoma. We discuss potential pitfalls in clinical and morphological diagnosis. The strong reactivity of the tumor cells with the nonspecific but ubiquitous mesenchymal marker vimentin in similar cases should direct early attention to the rare malignant bone tumor, epithelioid angiosarcoma, with subsequent confirmation of this diagnosis with specific immunohistochemical endothelial cell markers and/or electron microscopy.

Chordomas of the mediastinum: clinicopathologic, immunohistochemical, and ultrastructural study of six cases presenting as posterior mediastinal masses

Six cases of chordomas presenting as primary posterior mediastinal tumors are described. Three patients were female, and three were male between the ages of 8 and 65 years (mean, 40.6 years). In all cases, the tumors presented radiographically as relatively well-circumscribed, encapsulated soft tissue masses that did not seem to be related to the thoracic or dorsal spine. Only in one case, focal infiltration of bone at the level of T6-T7 was observed at the time of surgery. Histologically, the lesions showed a spectrum of features that ranged from sheets and cords of large cells with abundant vacuolated cytoplasm to small, stellate cells embedded within an abundant mucoid matrix. In one case, the cell population showed more pronounced nuclear atypia with loss of cytoplasmic vacuolization, frequent mitotic figures, necrosis, and solid areas characterized by a perivascular distribution of atypical spindle cells set against a myxoid stroma. Another case showed features of chondroid chordoma, with an immature chondroid-appearing matrix surrounding the atypical tumor cells. Immunohistochemical studies in all cases showed positive staining of the tumor cells with CAM 5.2 and broad-spectrum keratin, epithelial membrane antigen (EMA) and vimentin, and, to a lesser extent, with S-100 protein. Stains for muscle actin, carcinoembryonic antigen (CEA), and desmin were negative. Ultrastructural examination in two cases showed a spectrum of features that varied from large cells with abundant cytoplasm containing scattered ribosomes, glycogen granules, Golgi apparatti, abundant intermediate filaments, and small lumen formation with immature microvilli to smaller cells with elongated cytoplasmic processes, fewer intermediate filaments, rare desmosome type intercellular junctions, and complexes of mitochondria/rough endoplasmic reticulum. On clinical follow-up, two patients died with metastases to the lungs, chest wall, and liver from 1 to 3 years after diagnosis, and two patients are alive and well without evidence of disease after 3 and 16 years. Chordoma should be entertained in the differential diagnosis of posterior mediastinal tumors. Application of immunohistochemical stains or electron microscopy will be of aid in separating them from other conditions that may histologically closely resemble these lesions.