N. de Saint
Aubain Somerhausen
Institut Jules Bordet
I. INTRODUCTION
Myxoid material is composed of glycosaminoglycans, sulphated (chondroitin sulphate, keratan sulphate) and non sulphated (hyaluronic acid). It appears on H&E sections as a thin amorphous semitransparent substance, which may be confounded with edema. Its presence can be confirmed by special stains such as alcian blue and only chondroid substance (sulfated GAG) will remain positive after treatment by hyaluronidase.
Limited myxoid areas may be encountered in most soft tissue tumors and pseudotumors. The following discussion will only cover lesions which are typically myxoid (such as myxoid liposarcoma) or may occasionnally be predominantly myxoid (such as myxoid neurofibroma).
This encompasses a wide group of lesions and this large variety, coupled with their relative rarity explains the potential diagnostic difficulties.
Sampling represents an essential step to the diagnosis of myxoid lesions. In tumors which are not typically myxoid, myxoid changes will often hide at least some diagnostic features. For example, myxoid DFSP will usually lose its typical storiform pattern and will be difficult to distinguish from a myxoid neurofibroma. For these lesions, the identification of a solid component certainly represents the most important diagnostic clue. At the opposite, in some myxoid sarcomas which can have a solid component, the identification of myxoid areas may lead to the correct diagnosis. For example, the recognition of typical myxoid areas will allow to differentiate high grade myxofibrosarcoma from other pleomorphic (" MFH "-like) sarcomas.
Although it is difficult to propose an algorythmic approach of myxoid tumors, the combination of a few important features, summarized in table 5, will often provide a good basis for the differential diagnosis.
The relative frequencies of myxoid lesions, summarized in table 1 has to be kept in mind, as it seems wise to rule out the most common tumors before considering exceptionnal diagnosis. The most common benign myxoid lesions are nodular fasciitis, " ganglion " and myxoid neurofibroma. The more frequent myxoid sarcomas are, by far, myxofibrosarcoma and myxoid liposarcoma.
| Table 1. Myxoid tumors and pseudotumors | ||
| BENIGN | MALIGNANT | |
| A.MYXOID TUMORS | ||
| - Most common |
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| - Rare |
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| - Exceptionnal |
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| B. OTHER TUMORS WHICH ARE OCCASIONNALLY MYXOID | ||
| - Most common |
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| - Rare |
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| - Exceptionnal |
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As in general for soft tissue tumors, clinical data, including at least the age and sex of the patient as well as the precise location of the tumor are often primordial.
At low-power, general architectural features as well as the interface with adjacent tissues should always be studied. For example, the lobulation of dermal nerve sheath myxoma or the pattern of infiltration of DFSP are characteristic.
Vascularity is another important diagnostic element. Most benign lesions, specially " myxomas " are poorly vascularized , whereas myxofibrosarcoma and myxoid liposarcoma are characterized by a prominent vascular tree.
Nuclear atypia is often indicative of malignancy and allows the separation of myxofibrosarcoma from benign myxomas. However, because some malignant neoplasms (such as low-grade fibromyxoid sarcoma) lack significant atypia, it may be hazardous to assess the benign or malignant nature of a myxoid lesion without a precise diagnosis.
Immunohistochemistry is particularly helpful in the diagnosis of myxoid lesions and in our experience, the most valuable antibodies are S100 protein (nerve sheath differentiation, myoepithelial tumors, some myxoid liposarcomas and chondrosarcomas), smooth muscle actin (myxoid leiomyosarcoma, myofibroblastic lesions) and CD34 (DFSP, spindle cell lipoma...). The immunohistochemical pattern of most tumors is summarized in table 2.
A few specific cytogenetic aberrations (such as t(12;16) in myxoid liposarcoma, t(9;22) in extraskeletal myxoid chondrosarcoma or rearrangements of 12q in agressive angiomyxoma) may also have a diagnostic value.
| Table 2. Immunohistochemistry and karyotypic aberrations of myxoid tumors | |||||||
| SMA | S100 | CD34 | CK | Desmin | Others | Genetic alterations | |
| Myxoid nodular fasciitis | + | ||||||
| Myxoid neurofibroma | + | +/- | |||||
| Myxoid spindle cell lipoma | + | rearr. 13q, 16q | |||||
| Neurothekeoma | +++ | ||||||
| Agressive angiomyxoma | +/- | +/- | rearr. 12q | ||||
| OFMT | + (50%) | + | + (70%) | ||||
| Mixed tumor | +/- | + | + | +/- | GFAP +/- | ||
| Myxofibrosarcoma | +/- | ring (origin?) | |||||
| Myxoid / round cell liposarcoma | + (40%) | t(12;16), t(12;22) | |||||
| Extraskeletal myxoid chondrosarcoma | + (20%) | t(9;22) | |||||
| chordome | + | + | EMA + | ||||
| Myxoid DFSP / GC Fibroblastoma | +++ | ring /markers t(17;22) | |||||
| Myxoid leiomyosarcoma | + (90%) | + (20%) | + (50%) | ||||
| Myxoid MPNST | + (50%) | +/- | |||||
II. MOSTLY SUPERFICIAL MYXOID TUMORS
A. Most common (or less uncommon) benign myxoid lesions
1. " Ganglion "
Ganglion is probably the most common myxoid lesion. Ganglia occur in young adults, mostly females, with a predilection for the dorsal surface of the wrist, or fingers and toes. They appear as uni- or multilocular cystic mass frequently attached to the joint capsule or tendon sheaths. Histologically, thick walled cystic spaces are surrounded by connective tissue containing myxoid areas.
2. Nodular fasciitis
Nodular fasciitis is a rapidly growing lesion, usually present for only 1 or 2 weeks. Nodules are often small and superficial and occur in young adults, with a predilection for the forearm. Histologically, nodular fasciitis is composed of myofibroblasts (SMA +) arranged in a typical loosely textured " feathery " pattern. The stroma contains thin-walled capillaries, a mild lymphocytic infiltrate and occasionnal extravasated erythrocytes. Nodular fasciitis usually contains myxoid foci and approximately 5% of fasciitis are predominantly myxoid.
Predominantly myxoid lesions must be differentiated from low-grade myxofibrosarcoma (which is lobulated, shows significant nuclear atypia, and contains typical curvilinear vessels).
3. Myxoid neurofibroma
Myxoid neurofibromas are usually solitary lesions, occuring in adults, on the extremities. These lesions are well-circumscribed although unencapsulated and are composed of S100 protein positive spindle cells with wavy nuclei and indistinct cytoplasm, associated with wirelike collagen fibrils. Mast cells are usually easily found.
The presence of axons (NF +) and intralesional nerve bundles allows distinction from schwannoma and myxoid neurothekeoma. The presence of any mitotic activity supports a diagnosis of MPNST.
4. Myxoid spindle cell lipoma / Myxolipoma
Most myxoid benign lipomatous tumors are located in the head and neck region and represent myxoid spindle cell lipomas. This diagnosis, which should be considered in the differential diagnosis of most lesions occuring in the upper back / neck area, is suggested by the presence of an adipocytic component (sometimes lacking), " bipolar " spindle cells, ropey collagen bundles and mast cells, and is suported by CD34 positivity.
Myxoid changes, regarded as degenerative, may also be encountered in ordinary lipomas.
Both of these tumors are differentiated from myxoid liposarcoma by the absence of typical arborizing capillaries and lipoblasts.
B. Exceptionnal benign myxoid lesions
1. Myxoid neurothekeoma (dermal nerve sheath myxoma)
Myxoid neurothekeoma, also known as " dermal nerve sheath myxoma ", is a rare tumor of presumed nerve sheath origin, which affects adolescents and young adults, with a striking predilection for females. Most lesions are superficial and located in the upper limbs or head and neck area.
Histologically, myxoid neurothekeoma is characterized by a striking multinodular growth pattern. Lobules, often separated by fibrous septas, are composed of an abundant myxoid matrix containing spindle cells arranged in fascicles and whorls. Cells with a more epithelioid appearance are also often encountered. Mild nuclear pleomorphism and scattered mitoses are not uncommon. Immunohistochemically, myxoid neurothekeoma is strongly positive for S100 protein.
Myxoid neurothekeoma is a benign lesion cured by simple excision.
2. Superficial angiomyxoma
Superficial angiomyxoma is an underrecognized lesion which encompasses the majority of lesions referred in the earlier litterature as " cutaneous myxoma ".
Most cases present as cutaneous papules or polypoid lesions, with a predilection for the head and neck area and the trunk.
Superficial angiomyxoma is a poorly circumscribed lesion composed of myxoid nodules containing thin-walled capillaries and spindle-shaped or stellate fibroblasts (variably positive for CD34). The presence of neutrophils is typical. Strands of squamous or basaloid cells, or epidermoid cysts, which probably represent entrapped adnexal structures, are not uncommon.
S100 protein immunostaining helps to differentiate superficial angiomyxoma from myxoid neurothekeoma (which is more lobulated and less vascularized) and myxoid neurofibroma.
The vascular pattern, and the absence of nuclear atypia allows the distinction with low-grade myxofibrosarcoma.
Superficial angiomyxoma is a benign lesion but local recurrences are common after incomplete excision.
The identification of multiple lesions, or solitary lesions located in the breast or external ear should prompt further investigations as they are suggestive of Carney’s complex, an autosomal condition also featuring cardiac myoma, as well as pigmented skin lesions and endocrine abnormalities.
3. Ossifying fibromyxoid tumor (OFMT)
OFMT is a rare, recently characterized tumor of uncertain histogenesis. Most lesions are located within the subcutis on the extremities of middle-aged adults, with a male predominance.
OFMT is a well circumscribed, often multinodular tumor, composed of monotonous rounded cells arranged in cords in an abundant fibromyxoid matrix. A peripheral rim of mature lamellar bone is usually found in the thick fibrous capsule as well as in intralesionnal septas.
Cells are usually positive for S100 protein and are positive for desmin and smooth muscle actin in respectively 70% and 50% of cases.
The main differential diagnosis is mixed tumor of soft parts, which is positive for cytokeratins and often contains a more obvious epithelial component. Extraskeletal myxoid chondrosarcoma may also be considered.
OFMT is generally regarded as benign; recurrences occur in approximately 25% of cases.
Rare lesions (" atypical OFMT ") characterized by an increased cellularity, nuclear atypias, an increased mitotic rate (>2 per 10 HPF) and more randomly distributed osteoid containing neoplastic cells may behave more agressively and give rise to pulmonary metastases.
These lesions are separated from extraskeletal osteosarcoma by their resemblance to usual OFMT and their immunohistochemical profile.
4. Mixed tumor (myoepithelioma) of soft tissue
Tumors similar to mixed tumors or myoepitheliomas of salivary glands have recently been identified in subcutaneous and even subfacial soft tissues.
These lesions occur at any age, mostly in young adults, and there is a predilection for the limbs. Tumors are often well circumscribed. Their chondromyxoid stroma contains epithelial cells, arranged in cords and nests, and spindle shaped or plasmacytoid myoepithelial cells. Ductal differentiation is identified in a third of cases. Metaplastic bone or cartilage,and foci of adipocytic differentiation are occasionnally found. Immunohistochemically, most cases are positive for cytokeratins and S100 protein. Immunoreactivity for smooth muscle actin, desmin and GFAP is variable.
As for their salivary glands counterparts, the behavior of mixed tumors of soft tissue may be difficult to predict and although most of them are benign a few tumors metastasize.
The differential diagnosis between mixed tumors and extraskeletal myxoid chondrosarcoma may be extremely difficult on a morphologic basis and may rely on immunohistochemistry (positivity for keratins and smooth muscle actin in mixed tumors).
Tumors formerly known as " parachordoma " share the morphologic and immunohistochemical features of mixed tumors and these lesions probably represent a single entity.
5. Agressive angiomyxoma
This tumor occurs almost exclusively in the genital and perineal area of adult females, although rare cases have been reported in males.
Agressive angiomyxoma is a poorly circumscribed, slowly growing lesion composed of spindle-shaped and stellate cells evenly distributed in an abundant myxoid matrix. The lesion contains numerous vessels, often showing some hyalinization of their walls, and occasionnally surrounded by a few smooth muscle cells. Immunohistochemically, tumor cells may express desmin and/ or smooth muscle actin. Recent cytogenetic studies have revealed rearrangements of the 12q13-15 region.
Agressive angiomyxoma may behave agressively, with a recurrence rate of approximately 30%.
Agressive angiomyxoma must be distinguished from other mesenchymal tumors of the genital area: angiomyofibroblastoma and cellular angiofibroma, which are well circumscribed and usually don’t recur. Although earlier reports have suggested that desmin positivity could help to separate angiomyofibroblastoma and agressive angiomyxoma, it is now known that desmin may be expressed in both tumors. The distinction between these lesions may be extremely difficult as there may be some morphological overlap between these entities.
Fibroepithelial polyp, which is more superficial, exophtyic and contains multinucleated fibroblasts, may also be considered in the differential diagnosis
| Table 3. Differential diagnosis of vulval / perineal tumors | |||
| Aggr. angiomyxoma | Angiomyofibroblastoma | Cell. angiofibroma | |
| size | usually > 5cm | usually < 5 cm | small |
| borders | infiltrative | usually well circumscribed | well circumscribed |
| vessels | numerous, small to medium sized, often hyalinized | numerous capillaries | numerous, small to medium sized, often hyalinized |
| stroma cells | low cellularity spindle, stellate cells |
spindle, plump, multinucleated c. perivascular accentuation |
highly cellular bipolar spindle cells |
| stroma | myxoid to collagenous | edematous to collagenous | wispy collagen bundles |
| behavior | recurrences in 30% | no recurrences | no recurrences |
6. Digital Myxoma
Digital myxoma is a small dermal nodule located in the distal and dorsal portions of the fingers or, less commonly the toes, of adults. This well circumscribed lesion is composed of spindle-shaped or stellate fibroblasts lying in an abundant myxoid matrix.
C. Superficial myxoid sarcomas
1. Myxofibrosarcoma
Myxofibrosarcoma is in our experience one of the commonest soft tissue sarcomas but is probably still underrecognized.
Myxofibrosarcoma is a distinct clinicopathologic entity that encompasses a spectrum of lesions ranging from low-grade tumors, often unrecognized, to high-grade pleomorphic sarcomas resembling so-called " MFH " . The term " myxoid MFH " is still widely used but this seems unjustified as the MFH family has been progressively dismembered in the last few years and ultrastructural studies of myxofibrosarcoma support a fibroblastic rather than " histiocytic " line of differentiation.
Myxofibrosarcoma affects the extremities of older adults. Although the majority of tumors are superficial, approximately 30% of cases are deep seated. Most lesions show a multinodular growth pattern and have infiltrative margins.
Histologically, low-grade areas are composed of an abundant myxoid matrix containing small spindle-shaped or stellate cells with hyperchromatic nuclei. Cells with a mucin-containing vacuolated cytoplasm (" pseudolipoblasts ") are commonly found. The vasculature is typically composed of curvilinear capillaries, with some condensation of tumor cells around them. An inflammatory infiltrate is often present and may be prominent.
Intermediate grade lesions are characterized by areas of increased cellularity, increased mitotic activity and more marked cellular atypia; high-grade lesions show cellular pleomorphic " MFH "-like areas.
Immunohistochemically, all markers are negative at the exception of vimentin and of some focal positivity for smooth muscle actin in high-grade lesions.
Clinically, myxofibrosarcoma is characterized by a high recurrence rate (more than 50%), independant of the histologic grade (Table 4). In contrast, only intermediate and high-grade tumors carry a metastatic potential. The prognosis is significantly worse for deep lesions but this may be explained by the fact that these tumors are often larger and mostly high-grade.
An important characteristic of myxofibrosarcoma is its tendancy to become progressively higher grade in recurrences. This underlines the need for a complete excision of low-grade lesions, which are potentially curable but may acquire a metastatic potential with recurrences.
| Table 4. Prognosis of myxofibrosarcoma | |||
| Recurrences: 55% | |||
| Metastases: | Low grade | Superf.: / |
Deep seated: / |
| Int.- High grade | 25% | 35% | |
Low-grade myxofibrosarcoma is certainly underdiagnosed and is often confused with benign myxoid lesions. It is not uncommon that the correct diagnosis is only made after one or several recurrences.
The vascular pattern and the presence of nuclear atypia differentiates myxofibrosarcoma from intramuscular and juxtaarticular myxoma. Superficial angiomyxoma, which contains prominent vessels, also lack nuclear atypia. Myxoid neurofibroma is distinguished by its S100 positivity.
because of the similarity of their names, myxofibrosarcoma and low-grade fibromyxoid sarcoma are sometimes confused. Low-grade fibromyxoid sarcoma, which is has a significant metastatic potential, occurs in younger patients and is composed of bland spindle cells arranged in fascicles and whorls wihin a more collagenous stroma. Myxoid liposarcoma is usually well-circumscribed, has thinnner, branched capillaries and lack significant nuclear atypia.
The recognition of high-grade myxofibrosarcoma is also of importance as it carries a better prognostic than most other pleomorphic sarcomas such as myogenic sarcomas or unclassified MFH-like lesions.
2. Myxoid dermatofibrosarcoma protuberans
DFSP is a superficial lesion that occurs predominantly on the proximal extremities and the trunk of young to middle-aged adults. Histologically, DFSP is composed of monomorphic bland spindle cells arranged in a storiform pattern and infiltrating the subcutaneous adipose tissue in a typical " honeycomb " pattern. CD34 is consistently positive. DFSP is characterized by a very high recurrence rate.
In myxoid lesions, the storiform pattern is usually less pronounced and the vasculature may become prominent. Features supporting a diagnosis of DFSP are the pattern of infiltration of adipose tissue, and positivity for CD34. Cytogenetically, DFSP is characterized by ring and marker chromosomes composed of segments of chromosomes 17 and 22.
Myxoid DFSP is often difficult to differentiate from benign lesions such as neurofibroma. Immunohistochemistry is particularly helpful in this setting (although some positivity for CD34 is occasionnally encountered in nerve sheath tumors).
Giant-cell fibroblastoma has a number of similarities to DFSP.
This rare tumor affects mostly children, and is predominantly located in the trunk, back of thigh or inguinal area. Slender spindle cells are loosely arranged in an abundant myxohyaline matrix, characterized by the presence of typical pseudovascular spaces lined by multinucleated cells.
Giant cell fibroblastoma tends to infiltrate the subcutaneous fat in a fashion similar to DFSP, is also positive for CD34 and shares the karyotypic abnormalities of DFSP (ring and markers composed of t(17;22)).
In occasional tumors, areas of classical DFSP and giant-cell fibroblastoma coexist, and rare cases show the pattern of the other lesion in recurrences.
A. benign tumors
1. Intramuscular myxoma.
Intramuscular myxoma usually affects middle-aged adults, with a predilection for females. Tumors are confined to the large muscles of the thigh or upper arm. Lesions are usually solitary, although multiple lesions may be encountered in association with fibrous dysplasia.
Histologically, intramuscular myxoma is classically described as a paucicellular and hypovascular lesion. An abundant myxoid matrix contains bland spindle-shaped or stellate cells and rare muciphages; the vasculature is sparse. Although these lesions appear well-circumscribed, peripheral infiltration between muscle fibers is common.
Intramuscular myxoma don’t recur following adequate surgery.
The main differential diagnosis is with low-grade myxofibrosarcoma, which is characterized by nuclear atypia and curvilinear vessels. Clinical informations helps to differentiate intramuscular myxoma from juxta-articular myxoma, which is usually more cellular and have a significantly higher recurrence rate.
Occasionnal lesions may show areas of increased cellularity and vascularity. Whereas one study suggest that these changes do not influence their behavior, some authors consider that these tumors may recur (in 5 to 10% of cases) but, in contrast with low-grade myxofibrosarcoma, are not able to advance in histological grade, and have proposed the term " low-grade neoplasm with recurring potential ".
2. Juxta-articular myxoma
Juxta-articular myxoma resembles intramuscular myxoma, although it is often more cellular and vascularized. These lesions, which affect older patients and are located in the vicinity of large joints, especially the knee, may recur locally.
Juxta-articular myoma lack the nuclear atypia and the prominent curvilinear vasculature of myxofibrosarcoma.
1. Myxoid liposarcoma
Myxoid liposarcoma is discussed in more details with lipomatous tumors.
Briefly, myxoid liposarcoma tends to affect young adults and is usually deep seated, with a predilection for the thigh and polpliteal fossa. It is a well-circumscribed tumor characterized by branching thin-walled capillaries (" chicken wire " or " crow’s feet " pattern). Univacuolated lipoblasts are most commonly found in the peripheral regions.
Myxoid liposarcomas is characterized by a t(12;16) or rarely a t(12;22) trasnslocation.
Myxoid liposarcoma must be distinguished from myxofibrosarcoma (nuclera atypia, thicker curvilinear capillaries) and extraskeletal myxoid chondrosarcoma (virtually avascular).
2. Extraskeletal myxoid chondrosarcoma
Extraskeletal myxoid chondrosarcoma, also referred as chordoid sarcoma in earlier reports, affects adults, in their 3rd to 5th decades, with a male predominance. Most lesions are deep-seated, often intramuscular, and there is a strong predilection for the lower limb.
Extraskeletal myxoid chondrosarcoma is a multinodular tumor often traversed by fibrous septas. The hyaluronidase-resistant myxoid matrix usually appears almost avascular. Plump eosinophilic tumor cells are most commonly arranged in intersecting cords, although some lesions may be more cellular and simulate a myoepithelial tumor. Cytologic features are variable: tumors may be composed of spindle-shaped cells or round cells resembling PNET. Cytoplasmic hyaline " rhabdoid " inclusions are found in 10 to 20% of cases. Recently a few cases with epithelioid high-grade areas have been reported.
Immunohistochemically, S100 positivity is only seen in 10 to 35% of cases. Most tumors are characterized by a t(9;22) translocation.
Recent studies have demonstrated that the prognosis of myxoid chondrosarcoma is poorer than suggested by earlier reports, with a metastatic rate of approximately 45%.
EMC must distinguished from chordoma, which is usually axial and is positive for epithelial markers and from myxoid liposarcoma, which shows a plexiform vascular pattern. Cellular tumors are virtually indistinguishable from mixed tumors without immunohistochemistry (positivity for keratins and smooth muscle actin in mixed tumors).
Chondrosarcoma of bone may appear predominantly myxoid but usually contains more mature cartilage and does not show the lace-like pattern of EMC; the t(9;22) translocation is absent.
3. Low-grade fibromyxoid sarcoma
This rare and recently characterized tumor tends to affect young adults, with a predilection for limb girdles. Histologically, low-grade fibromyxoid sarcoma is characterized by an alternance of collagenous and myxoid areas. The tumor is remarkable by the bland, benign appearance of its fibroblastic spindle cells, often arranged in a whorled pattern. Mitoses are scarce. Immunohistochemical stains are usually negative at the exception of vimentin.
Despite its bland cytologic features, distant metastases, chiefly to the lungs, eventually occur in approximately half of the cases, usually after a long disease-free interval.
Although their names are relatively similar, low-grade fibromyxoid sarcoma is distinct form low-grade myxofibrosarcoma, which occurs in older patients, is more uniformly myxoid, contains curvilinear vessels and shows greater nuclear atypia.
4. Chordoma
Chordoma is a bone tumor which may occasionally present clinically as a soft tissue mass.
It affects adults in their fifth to seventh decades and exclusively occurs in axial locations (mainly the base of skull, cervical spine and sacrococcygeal area). Histologically, chordoma is a lobulated tumor composed of a an admixture of large multivacuolated (" physaliphorous ") cells and cuboidal cells, arranged in cords, sheets and nests in a hyaluronidase resistant myxoid matrix.
Chordoma is positive for epithelial markers (cytokeratins, EMA) and commonly expresses S100 protein.
The main differential diagnosis is myxoid chondrosarcoma, which is negative for epithelial markers.
5. Myxoid MPNST
MPNST is characterized by a varying cellularity, with occasionnal myxoid areas. However, predominantly myxoid MPNSTs are uncommon (approximately 10% of cases).
Approximately 30% of patients have neurofibromatosis type I and tumors are often in close association with a nerve. Histologically, the diagnosis is suggested by cytologic features (spindle shaped cells with pale, ill-defined cytoplasm, and elongated or wavy nuclei), the frequent perivascular condensation of tumor cells, and the occasional finding of heterologous elements (rhabdomyoblasts, chondrosarcomatous or osteosarcomatous components). S100 protein is only positive in half of the cases.
The identification of (any) mitotic activity and nuclear atypia distinguishes MPNST from neurofibroma. MPNST must also be differentiated from leiomyosarcoma (actine and/or desmin positive) and other spindle cell sarcomas (synovial sarcoma...)
6. Miscellaneous
Myxopapillary ependymoma may occasionnally present as a soft tissue tumor, typically in the sacral area. Histologically, small eosinophilic GFAP positive cells are arranged around vascular cores. The differential diagnosis includes chordoma and extraskeletal myxoid chondrosarcoma.
The rare myxoid leiomyosarcoma, which may be encountered in a wide variety of sites, shows areas with typical cytologic and immunohistochemical (smooth muscle actin invariably positive, desmin positive in 70% of cases) features of smooth muscle differentiation.
In rare instances, synovial sarcoma (EMA +, Ker +, CD99 +, S100 +/-) and solitary fibrous tumor (CD34 +, CD99 +) may appear predominantly myxoid, particularly on small biopsy specimen.
| B. Deep-seated tumors |
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| - intramuscular myxoma | ad. F>M |
extremities, intramuscular | poorly circumscribed (entrapped muscle) | paucivascular | no atypia | benign |
| - juxta-articular myxoma | ad. M>F |
around large joints | paucivascular | no atypia | benign ccasional recurrences |
|
| - myxoid liposarcoma | ad. | extremities | well circumscribed | branching thin-walled capillaries | mucin pooling lipoblasts (periphery) |
rarely metastasize if purely myxoid |
| - ES myxoid chodrosarcoma | ad. | extremities | well-circumscribed lobulated |
virtually avascular | hyaluronidase resistant fibrous septa lace-like pattern |
malignant, late metastases |
| - Low-grade fibromyx. sarc. | ad. | extremities, trunk | minimal atypia alternance fibrous / myxoid areas whorled pattern |
malignant, late metastases | ||
| - chordoma | ad. | axial locations | physalyphorous cells | malignant | ||
| - myxoid MPNST | ad. | extremities, trunk often close to nerves |
perivascular condensation | malignant | ||
| - myxoid leiomyosarcoma | ad. | perineum, extremities | eosinophilic sp. cells | malignant | ||
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