Parachordoma is immunohistochemically and cytogenetically distinct from axial chordoma and extraskeletal myxoid chondrosarcoma

Diagnosing an extra-axial chordoma of the proximal tibia with the help of brachyury, a molecule required for notochordal differentiation

Chordomas are rare malignant bone tumours considered to arise from notochordal remnants that persist in the axial skeleton. Although their morphology can resemble that of a carcinoma, chondrosarcoma or malignant melanoma, the axial location and their well-defined immunophenotype, including expression of cytokeratins (CK7/20/8/18/19) and S100, generally allow the diagnosis to be made with confidence once the possibility is considered. In contrast, making a robust diagnosis of an extra-axial chordoma has been difficult in the absence of specific markers for chordomas. We have recently shown in gene expression microarray and immunohistochemistry studies that brachyury, a transcription factor crucial for notochordal development, is a specific and sensitive maker for chordomas. We now present a case of an intracortical tibial tumour, with detailed report of the imaging, and morphological features consistent with a chordoma, where notochordal differentiation was demonstrated with an antibody to brachyury. The tumour cells were also positive for cytokeratins, including CK19, and S100, CEA, EMA and HMBE1, findings which support the diagnosis of chordoma. Brachyury can be employed as a marker of notochordal differentiation and help identify confidently, for the first time, extra-axial bone and soft tissue chordomas, and tumours which may show focal notochordal differentiation.

Extra-Axial Chordoma

Chordomas are low-grade malignant tumors of bone that occur almost exclusively in the axial skeleton. Other neoplasms with a similar histologic picture but an extra-axial location have been described, including parachordoma, myxoid chondrosarcoma, and extra-axial chordoma. We herein present another case of the rare extra-axial chordoma. A 41-year-old woman developed an 8.3 cm mass in the pubic bone. The gross, microscopic, and immunohistochemical findings were identical to those of a classic chordoma. Parachordoma and myxoid chondrosarcoma were excluded from the differential diagnosis. Five previously reported cases of extra-axial chordoma were reviewed and found also to demonstrate clinical and pathologic features specific to chordoma, despite arising in an extra-axial location. Although rare, extra-axial chordoma does exist and should be recognized and managed in a similar fashion to its well-described counterpart. It must be differentiated from other histologic mimics, because the treatment and prognosis can differ significantly.

Brachyury, a crucial regulator of notochordal development, is a novel biomarker for chordomas

Chordomas are malignant tumours that occur along the spine and are thought to derive from notochordal remnants. There is significant morphological variability between and within chordomas, with some showing prominent areas of chondroid differentiation. Our microarray data from a broad range of connective tissue neoplasms indicate that, at the transcriptional level, chordomas resemble cartilaginous neoplasms. Here we show that chordomas express many genes known to be involved in cartilage development, but they also uniquely express genes distinguishing them from chondroid neoplasms. The brachyury transcription factor, known to be involved in notochordal development, is only expressed by chordomas. Using a polyclonal antibody, we show that brachyury is expressed in the embryonic notochord and in all 53 chordomas analysed, labelling both chondroid and chordoid areas of these tumours. In contrast, the protein was not detected in over 300 neoplasms, including 163 chondroid tumours. Brachyury was not detected in the nucleus pulposus, arguing against the hypothesis that this tissue derives directly from the notochord. These data provide compelling evidence that chordomas derive from notochord and demonstrate that brachyury is a specific marker for the notochord and notochord-derived tumours.

Cutaneous metastatic chordoma with concomitant tuberous sclerosis

BACKGROUND

Chordomas are rare malignant tumors of notochord origin and are locally aggressive with a metastatic potential. Of noted interest, the skin rarely is seen as a metastatic site.

METHODS AND OBSERVATIONS

We describe a 20-month-old infant whose primary presentation of a clivus-based chordoma was multiple asymptomatic cutaneous nodules. A skin biopsy showed large vacuolated cells embedded in a myxoid stroma. Immunohistochemical staining was positive for S-100, keratin, and epithelial membrane antigen markers consistent with malignant chordoma. Magnetic resonance imaging revealed a clivus-based chordoma with scattered metastases within the neuraxis and multiple visceral sites. Further examination also revealed a diagnosis of tuberous sclerosis.

LIMITATIONS

An observed association between chordoma and tuberous sclerosis cannot be established firmly on the basis of a case report.

CONCLUSIONS

This case illustrates a diagnostic challenge because of the unusual presentation of an already rare tumor. By reporting our case, we hope to assist in the recognition of this rare dermal condition and highlight the speculated coexistence of tuberous sclerosis with chordoma tumors.

Unusual variants of malignant melanoma

A potential diagnostic pitfall in the histologic assessment of melanoma is the inability to recognize unusual melanoma variants. Of these, the more treacherous examples include the desmoplastic melanoma, the nevoid melanoma, the so-called 'minimal-deviation melanoma,' melanoma with prominent pigment synthesis or 'animal-type melanoma,' and the malignant blue nevus. Also problematic are the unusual phenotypic profiles seen in vertical growth phase melanomas; these include those tumors whose morphological peculiarities mimic cancers of nonmelanocytic lineage and those melanomas that express aberrant antigenic profiles not commonly associated with a melanocytic histogenesis. Metaplastic change in melanoma, balloon cell melanoma, signet-ring cell melanoma, myxoid melanoma, small cell melanoma and rhabdoid melanoma all have the potential to mimic metastatic and primary neoplasms of different lineage derivations. Abnormal immunohistochemical expression of CD 34, cytokeratins, epithelial membrane antigen, and smooth muscle markers as well as the deficient expression of S100 protein and melanocyte lineage-specific markers such as GP100 protein (ie HMB-45 antibody) and A103 (ie Melan-A) also present confusing diagnostic challenges. In this review, we will discuss in some detail certain of these novel clinicopathologic types of melanoma, as well as the abnormal phenotypic expressions seen in vertical growth phase melanoma.

[Myoepithelioma of soft tissue -- case report with clinicopathologic, ultrastructural, and cytogenetic findings]

The case of a soft tissue myoepithelioma is presented including clinicopathologic, ultrastructural, and genetic findings. A 30-year-old male patient suffered from a soft tissue tumor within the deep soft tissues of the right lower leg measuring 13.2 x 8.2 x 9 cm. Histologically, the lesion was diagnosed as a myoepithelioma displaying a lobulated architecture with cords and nests of epithelioid and spindle cells without cytologic atypia lying within a fibromyxoid and partly chondroid matrix; immunohistochemistry was positive for pancytokeratin, S100-protein, calponin and partly for GFAP and EMA. Ultrastructural analysis revealed glycogen deposits and cell-membrane-associated plaque structures, whereas true myofilaments could not be identified (with immunohistochemistry being negative for actin). Using comparative genomic hybridization (CGH), a gain of chromosome Y was detected. A loss on 17p could not be detected unambiguously. However, based on the low resolution of CGH a small loss cannot be excluded. The patient was free of disease 25 months following complete tumor resection. Myoepitheliomas/mixed tumors of deep soft tissue represent rare soft tissue lesions that may reach a considerable size and may mimic other soft tissue tumors or sarcomas. Based on a local relapse rate of approximately 20% according to the literature, a complete resection with thorough follow-up should be recommended.

Extraskeletal myxoid chondrosarcoma: updated clinicopathological and molecular genetic characteristics

Extraskeletal myxoid chondrosarcoma (EMC) is a rare soft-tissue sarcoma characterized by distinctive morphological and cytogenetical features. As its name implies, EMC was believed to represent a variant of soft-tissue chondrosarcoma owing to its histological resemblance to chondroblastic tissue in the early stages of cartilage development or chondroid tumors such as skeletal chondrosarcoma. However, the chondroid nature has been a subject of controversy, and its line of differentiation remains to be determined. Consequently, the tumor is provisionally classified into a group of tumors of uncertain differentiation in the revised World Health Organization classification of tumors of soft tissue and bone. Moreover, immunohistochemical and ultrastructural features of neural or neuroendocrine differentiation have been recently reported in a subset of EMC, providing a new insight into their histogenetic nature. Chromosomal rearrangements involving 9q22, such as t(9;22)(q22;q12), and resultant NR4A3 fusion genes are tumor-type specific or pathognomotic for this entity and are assumed to play an important role in the development of EMC. Although the biological mechanisms and functions are largely unknown, the NR4A3-related pathway is considered a potential molecular target for future therapeutic intervention. Because of its protracted but resilient nature, a tenacious and long-term follow up is necessary for any patient.

Parachordoma is not distinguishable from axial chordoma using immunohistochemistry

Parachordoma is a rare soft tissue tumor that morphologically resembles chordoma of the axial skeleton but occurs in a peripheral site. A recent study reported immunohistochemical differences between chordoma and parachordoma. While both tumors were positive for cytokeratin (CK) 8/18 (as recognized by the antibody Cam5.2), S100 and epithelial membrane antigen (EMA), only the chordoma was positive for CK7, CK20, CK 1/5/10/14 (as recognized by the antibody 34betaE12) and carcinoembryonic antigen (CEA). It has since been suggested that tumors indistinguishable from chordoma that involve the periphery should be termed chordoma periphericum and that these tumors are distinct from parachordoma. In the current study, the clinical, radiological, pathological, immunohistochemical and ultrastructural features of a chordoma-like tumor involving the deep soft tissues of the lower leg of a 69-year-old woman are presented. Microscopically, the tumor had a pseudolobulated growth pattern and consisted of sheets, nests and cords of epithelioid cells, some with a physaliferous appearance, separated by abundant myxoid stroma. The tumor cells were positive for CK 8/18, EMA and S100, showed focal staining for CK7, and were negative for CK20, CK 1/5/10/14 and CEA. On the basis of these results a diagnosis of parachordoma was favored. For comparison, an immunohistochemical analysis of five axial chordomas was also performed. The chordomas showed positivity for CK 8/18 (5 of 5 cases), EMA (5 of 5 cases), S100 (5 of 5 cases), CK 1/5/10/14 (1 of 5 cases) and CK7 (1 of 5 cases). Stains for CK20 and CEA were negative in all five chordomas. The results of the present study suggest that the expression of antigens for CK 1/5/10/14, CK7, CK20 and CEA in chordoma might not be as common as what has been previously reported. The results also suggest that parachordoma might not be easily distinguished immunohistochemically from axial chordoma (and therefore also from so-called chordoma periphericum).

Extraskeletal myxoid chondrosarcomas do not show a chondrocytic phenotype

Extraskeletal myxoid chondrosarcoma is a rare mesenchymal soft-tissue malignancy of putative chondrocytic differentiation. Occasional overt cartilage formation, positivity for S-100 protein, and ultrastructural analysis have supported this view. However, most extraskeletal myxoid chondrosarcomas do not show chondroid tissue formation, and S-100 protein is found much less commonly than has been reported. Both these observations cast doubt on the histogenetic classification of extraskeletal myxoid chondrosarcoma as a chondroblastic entity. Mostly using matrix proteins as markers of mesenchymal cell differentiation, we investigated the biochemical matrix composition and cellular phenotype of the tumor cells in representative specimens from 14 extraskeletal myxoid chondrosarcomas. In all but one tumor specimen, which showed histomorphologically overt cartilage formation, only occasional staining for the proteoglycan aggrecan was found. Specimens from two tumors showed presence of collagen type II, and none was positive for collagen type X. Instead, collagen types I, III, and VI were diffusely positive. Also, S-100 protein was largely absent. Our results suggest that the basic cellular phenotype of extraskeletal myxoid chondrosarcoma is not chondrocytic or prechondrocytic and that extraskeletal myxoid chondrosarcoma is not a chondrosarcomatous entity. Extraskeletal myxoid chondrosarcoma consists most likely of primitive mesenchymal cells with focal, multidirectional differentiation. Chondrocytic differentiation is an unusual facet in the spectrum of differentiation patterns exhibited by these lesions.

Myoepithelial tumors of soft tissue: a clinicopathologic and immunohistochemical study of 101 cases with evaluation of prognostic parameters

Myoepitheliomas and mixed tumors were only recently recognized to occur primarily in soft tissue, and only small case numbers have been described. To characterize these tumors further and to evaluate prognostic parameters, 101 myoepithelial tumors of soft tissue were retrieved from the authors' consult files. Hematoxylin and eosin sections were reexamined, immunohistochemistry was performed, and clinical details were obtained from referring physicians. Fifty-three patients were male and 48 female (mean age 38 years; range 3-83 years). Tumor size ranged from 0.7 to 20 cm (mean 4.7 cm). Most tumors arose in the extremities and limb girdles: 41 in the lower limbs, 35 in the upper limbs, 15 in the head and neck, and 10 in the trunk. Fifty-four tumors were situated in subcutis and 37 in deep soft tissue (depth unstated in 10). Most cases were grossly well circumscribed; 43 showed microscopically infiltrative margins. Histologically, most tumors were lobulated, composed of cords or nests of epithelioid, ovoid, or spindled cells with a variably reticular architecture and a chondromyxoid or collagenous/hyalinized stroma. Eight cases showed a predominantly solid proliferation of spindled or plasmacytoid cells; 17 demonstrated ductular differentiation (mixed tumors). Cartilage was present in 6 cases, 6 contained bone, and 4 others contained both. Mitoses ranged from 0 to 68 per 10 high power fields (mean 4.7 per 10 high power fields). Tumors with benign cytomorphology or mild cytologic atypia (low-grade) were classified as myoepithelioma or mixed tumor, whereas tumors with moderate to severe atypia (high-grade) were classified as myoepithelial carcinoma (epithelioid or spindled cells with vesicular or coarse chromatin, prominent, often large nucleoli, or nuclear pleomorphism) or malignant mixed tumor (cytologically malignant cartilage or bone). Sixty-one cases were myoepitheliomas or mixed tumors, and 40 were myoepithelial carcinomas or malignant mixed tumors. By immunohistochemistry, all cases with available material were reactive for epithelial markers (keratins and/or epithelial membrane antigen): 90 of 97 (93%) expressed keratins (most often AE1/AE3 or PAN-K), 84 of 97 (87%) S-100 protein, 44 of 51 (86%) calponin, 52 of 83 (63%) epithelial membrane antigen, 40 of 87 (46%) glial fibrillary acidic protein, 27 of 75 (36%) smooth muscle actin, 15 of 66 (23%) p63, and 7 of 51 (14%) desmin. Follow-up was available for 64 patients. Among 33 cases with benign or low-grade cytology (mean follow-up 36 months; range 4-168 months), 6 recurred locally (18%) and none metastasized. No clinical or histologic features correlated with recurrence. Among 31 cytologically malignant cases (mean follow-up 50 months; range 4-252 months), 13 recurred locally (42%) and 10 metastasized (32%); so far, 4 patients have died of metastatic tumor. This study expands the spectrum of myoepithelial tumors of soft tissue to include myoepithelial carcinomas and malignant mixed tumors, which pursue an aggressive clinical course. Although the majority of morphologically benign or low-grade myoepithelial neoplasms of soft tissue behave in a benign fashion, there is an approximate 20% risk for local recurrence.

Parachordoma with multiple metastases

We present a very rare case of parachordoma with local aggressiveness and widespread metastases. A 68-year-old male presented with a mass in his left calf. The lesion was depicted as a poorly marginated mass with inhomogeneous signal intensity on magnetic resonance imaging. The tumor invaded surrounding muscles, neurovascular bundles, and bones. Widespread metastasis to lung, bone, and skin developed after amputation surgery. The histologic features of primary and metastatic lesions were the same and consistent with parachordoma.

Parachordoma or chordoma periphericum? Case report of a tumor of the thoracic wall

We report the findings from an aspiration biopsy and resection of a chordoma-like tumorous mass in the wall of the thorax of a 36-yr-old man with immunohistochemical, ultrastructural, and cytogenetic studies. The 4-cm oval tumor was an incidental finding on physical examination, and no other lesions were identified after comprehensive radiologic studies. The aspirate was composed of sheets and nests of cells with distinct borders in a myxoid and fibrillary extracellular matrix. The neoplastic cells were uniform and round or polygonal with abundant pale blue vacuolated cytoplasm and small round, central or eccentric nuclei. On electron microscopy, mitochondrial rough endoplasmic reticulum complexes were seen in neoplastic cells. These features were similar to those of a conventional chordoma. However, the cytogenetic pattern, 43, XY ,-1, -2, der (5)t(1p;5q), -6, add(8p) ,add(10q), was not typical. In addition, the neoplastic cells were positive for vimentin, S-100, AE1/AE3, CAM 5.2, and CK 19; were focally positive for EMA and smooth muscle actin; and were negative for cytokeratin 1 and 10 (34 beta E12), CK 7, CK 8 (35H 11B), CK 17, and CK 20. The cytogenetic and immunohistochemical patterns were different from conventional chordoma and its peripheral counterpart, chordoma periphericum, suggesting the diagnosis of parachordoma. To the best of our knowledge, this is the first report of fine-needle aspiration of this newly defined and rare entity.

Hyaline cell-rich chondroid syringoma: case report and review of the literature

Hyaline cell-rich chondroid syringoma (HCRCS) is a rare benign cutaneous neoplasm composed of cells with eosinophilic hyaline cytoplasm and plasmacytoid features, the origin of which remains elusive. To the best of our knowledge, only eight cases of this entity have been reported so far, and none of them was submitted to a large panel of myoepithelial markers. We report on a case of a previously healthy 29-year-old male patient who presented with a slowly enlarging flesh-colored nodule on the palmar aspect of the tenar region of his left hand, measuring 2 cm in maximum diameter. The nodule was "shelled-out" and submitted to light microscopy, immunohistochemistry, and ultrastructural examination. Histopathologic analysis disclosed a lobulated neoplasm composed of hyaline cells with plasmacytoid features showing ovoid nuclei, with occasional invaginations, finely granular chromatin, and discrete nucleoli; the cytoplasm was deeply eosinophilic with occasional dot-shaped paranuclear hyaline inclusions. On immunohistochemical evaluation, hyaline cells were strongly and diffusely positive for S-100 protein, vimentin, pan (CAM 5.2) and high molecular weight (34betaE12) cytokeratins; these cells were focally positive for GFAP, maspin, neuron-specific enolase, and cytokeratin 14. Alpha-smooth muscle actin, epithelial membrane antigen, carcinoembryonic antigen, collagen IV, Gp100 (HMB-45), and p63 were negative in neoplastic hyaline cells. Ultrastructural analysis disclosed cells with ovoid nuclei showing occasional invaginations and nuclear pockets; the cytoplasm was rich in meshworks of non-bundling intermediate filaments and a variable amount of rough endoplasmic reticulum cisternae. Based on our findings and those previously reported, hyaline cells of HCRCS might posses an aberrant myoepithelial differentiation. Most importantly, pathologists need to be aware of the histologic and immunohistochemical features of HCRCS to avoid a misdiagnosis of highly malignant neoplams, such as malignant melanoma and extra-skeletal myxoid chondrosarcoma.

Myoepithelioma of the vulva

The histologic diagnosis of myoepithelioma is often problematic. We here describe a case of myoepithelioma, composed exclusively of neoplastic myoepithelial cells, in the vulva of a 52-year-old female. The vulva is a very rare site for this neoplasm. A subcutaneous tumor measuring 3.0 x 2.5 x 2.0 cm displayed a multinodular growth pattern. Histologically, it was characterized by epithelioid, trabecular, cord, solid, or reticular arrangements of tumor cells and markedly hyalinized stroma. The tumor cells were large and polygonal with eccentrically located round to oval nuclei with prominent nucleoli and eosinophilic cytoplasm. Some cells had clear cytoplasm. Moderate cellular atypia was seen and there were 4 mitotic figures per 10 high-power fields. No ductal architecture was found and there were no areas of chondroid or osseous differentiation. There was no destructive invasive growth. Immunohistochemically the tumor was positive for vimentin, epithelial membrane antigen, wide keratin, alpha-smooth muscle actin, S-100 protein, and glial fibrillary acidic protein. The patient was well and free of disease at 6 months. This neoplasm should be distinguished from other epithelial and mesenchymal neoplasms as it shows a different clinical behavior.

Clear cell atypical fibroxanthoma:a clinicopathologic study

INTRODUCTION

The atypical fibroxanthoma (AFX) is considered by most authorities to represent a superficial or minimally invasive variant of malignant fibrous histiocytoma that most often presents as a solitary nodule on the sun-exposed skin of the elderly. Among the rarest variants is the clear cell AFX, a lesion which raises consideration to a differential diagnosis encompassing a variety of neoplastic and non-neoplastic clear cell proliferations.

METHODS

We describe three cases of a distinctive cutaneous neoplasm arising in the sun-exposed skin of elderly patients. In all cases, formalin-fixed, paraffin-embedded tissue was available for analysis. The histology in concert with the immunophenotype was held to be diagnostic of the clear cell variant of AFX.

RESULTS

All tumors comprised sheets of large cells with foamy cytoplasms and hyperchromatic, polyploid nuclei manifesting frequent and atypical mitoses. The critical cells in our cases expressed CD68 but none of CD3, CD20, CD34, S-100 protein, muscle-specific actin, factor XIIIa, Melan-A, carcinoembryonic antigen, or cytokeratin.

CONCLUSION

Although typical examples of AFX provoke diagnostic consideration of spindle cell cancers of the skin (most often spindle cell melanoma, spindle cell squamous cell carcinoma, and leiomyosarcoma), the clear cell variant raises other differential diagnostic considerations instead. These include balloon cell melanoma, sebaceous carcinoma, pleomorphic liposarcoma, chordoma, parachordoma, tricholemmal carcinoma and clear cell squamous cell carcinoma. A diagnosis of AFX is one of exclusion; one must employ immunohistochemical markers to rule out the aforementioned differential diagnostic considerations. By reporting the fifth, sixth and seventh cases of clear cell AFX, we hope to alert dermatopathologists to this distinctive and unusual neoplasm, recognition of which is essential to avoid under- or over-diagnosis and inappropriate therapy.

Radiographic, computed tomographic and histopathologic appearance of a presumed spinal chordoma in a dog

A 4-year-old Labrador Retriever presented for urinary incontinence and constipation of 2 weeks duration. There was a tender abdomen, lumbar pain and conscious proprioceptive deficits in both pelvic limbs. Depressed pelvic limb reflexes were present consistent with a lower motor neuron lesion. In radiographs of the lumbar spine there was narrowing of the intervertebral disc space at L5-L6 with irregular, multifocal areas of mineralized opacities dorsal to the intervertebral disc space, presumably within the vertebral canal. On computed tomography, an intramedullary, partially mineralized mass was identified in the spinal cord at the level of caudal L5 through cranial L6. At necropsy there was a four-centimeter enlarged, irregular segment of spinal cord at the level of L5-L6. When sectioned, the spinal cord bad a mineralized texture. Histologically there were variable sized cells that were stellate in appearance with vacuolated cytoplasm (physaliferous cells) and mucinous background consistent with a chordoma. Chordoma is a rare, skeletal neoplasm that originates from mesoderm-derived notochord and has been reported in humans and animals. Extraskeletal development of a chordoma within the spinal cord is a rare manifestation of this neoplasm. However, based on other reports in dogs, solitary extraskeletal locations of chordomas may be the typical expression of this neoplasm in the dog. Differentiation of similar histologically appearing tumors, such as a parachordoma or myxoid chondrosarcoma, will require immunohistochemical characterization of these tumors in veterinary patients.

Chordoma periphericum: a case report

The authors describe a tumor that had the histologic and ultrastructural features and immunohistochemical profile of an axial chordoma, but arose in the distal ulna. A skeletal survey failed to show any other site of involvement. The tumor was resected, and the patient remains free of disease 2 1/2 years later. Rare tumors with the histologic features of chordoma have been reported in appendicular locations. Chordoma periphericum, a tumor that has the potential to metastasize, needs to be distinguished from parachordoma because no classic parachordoma has been reported to disseminate.

Parachordoma of the tibia: report of a rare case

We report a case of recurrent parachordoma of the left anterior tibial region in a 64-year-old male patient. The tumor was a periosteal tender mass, and, histologically, displayed vague nodules of spindle to rounded eosinophilic cells embedded in a myxoid matrix. Large vacuolated (physalphorouslike) cells were noted as in sacrococcygeal chordoma. This tumor should be differentiated from myxoid chondrosarcoma, myxoid liposarcoma, chondromyxoid fibroma, and metastatic chordoma. The presence of physaliphorous cells in the tumor with positive immunoreactions caused by cytokeratin rules out the diagnosis of another myxoid tumor. The differential diagnosis from metastatic chordoma is basically made by clinicians. Even though parachordoma is usually regarded as a benign soft tissue neoplasm, two recurrences occurred in our case. Since the reported cases, including ours, have diverse clinical courses, it is essential to follow-up the patient carefully.

Myxoma is not a single entity: a review of the concept of myxoma

Myxoid lesions can be subdivided into (1) mainstream myxomas of soft tissues, (2) mainstream myxomas located outside the soft tissue, (3) inadequately substantiated myxomas, (4) myxoid soft tissue tumors or lesions not regarded as myxomas, (5) myxoid fatty conditions, (6) other soft tissue lesions and tumors that are sometimes markedly myxoid, (7) other soft tissue tumors in which myxoid foci may be seen, and (8) nonneoplastic myxoid conditions of soft tissue. More than 60 such conditions are listed and the five entities regarded as mainstream soft tissue myxomas (namely, intramuscular myxoma, juxta-articular myxoma, superficial angiomyxoma, aggressive angiomyxoma, and myxoid neurothekeoma [myxoma of nerve sheath]) are reviewed in detail. Intramuscular myxoma is exclusively intramuscular, usually affects middle-aged women, is most commonly located in the thigh, and does not recur after simple excision. Multiple intramuscular myxomas are rare and are usually associated with monostotic or polyostotic fibrous dysplasia and Albright's syndrome. Juxta-articular myxoma histologically resembles an intramuscular myxoma, but involves periarticular tendons, ligaments, joint capsules, muscles, and even the subcutis of adults. It may be associated with osteoarthritis of the adjacent joint. Some 30% recur locally. Superficial angiomyxoma also has been called cutaneous myxoma. It affects all ages, with a peak incidence in the third and fourth decades; arises in the trunk, lower limb, head, and neck regions; and usually measures less than 5 cm in diameter. Epithelial components are present in approximately 25% of tumors. Approximately one third recur locally, but there have been no metastases. Patients with multiple lesions may have the Carney complex. Aggressive angiomyxoma usually arises in the pelvic and perineal regions and affects females seven times as often as males. Tumors usually measure 10 cm or more in diameter, invade surrounding tissues, and recur in approximately 50% of cases. None have metastasized. Myxoma of nerve sheath (the myxoid variant of neurothekeoma) preferentially affects the dermis and subcutis of the cervicofacial areas and shoulders of young women. Most patients are younger than 40 years; one third of them are in the second decade of life. The majority of tumors measure between 0.5 and 1.5 cm. Only three of 102 cases compiled from the two largest published series recurred; none metastasized. The different clinicopathologic features and behavior of these five mainstream myxomas indicate that myxoma is not a single entity.