LIPOMATOUS TUMORS OF SOFT TISSUES
N. de Saint
Aubain Somerhausen
Institut Jules Bordet
1. Introduction
Lipomatous tumours are the most common soft tissue neoplasms. These lesions, which can occur at every age and at almost any anatomical location are part of the daily practice of every surgical pathologist. Although most of them are ordinary lipomas, easily diagnosed, the identification of atypical lipomas and well-differentiated liposarcomas can be a challenge and there is still some confusion between these terms. Morphological variants of benign and malignant lipomatous tumors may also cause diagnostic problems and must be recognized in order to avoid inappropriate therapy. Finally, whereas some other lesions containing adipose tissue may be mistaken for lipomatous neoplasms, the recognition of the adipocytic differentiation of some tumours such as spindle cell lipoma or round cell liposarcoma may be problematic.
We believe that the awareness of the existence of the various clinicopathologic entities, and of their main characteristics, is essential to avoid diagnostic pitfalls. Therefore, we will attempt to provide a practical review of these lesions, emphasizing on diagnostic clues and differential diagnosis. Our approach to their differential diagnosis will be to group these lesions according to the amount of their fatty component: lesions composed predominantly of adipocytes, lesions accompanied by other connective tissue elements, and lipomatous tumors in whom the lipomatous differentiation is not always obvious.
Histologic features which should be analyzed when examining a lipomatous lesion include the pattern of lobulation, the presence of other connective tissue elements, the regularity in size of adipocytes, the presence of atypical cells and lipoblasts.
It is important to remember that lipoblasts are not only characterized by the presence of lipid droplets scalloping their nuclei but should also show some nuclear enlargement and hyperchromatism, which differentiates them from atrophic adipocytes or foamy macrophages.
Lipomatous tumors are usually diagnosed on light-microscopic morphology alone. In our view, special stains for lipids (oil red O or Sudan), which are prone to technical artefacts, do not provide any valuable information. Immunohistochemistry is also of limited value, although staining for S100 protein may help to identify lipoblasts, and positivity for CD34 may support a diagnosis of spindle cell lipoma. Although presently it can hardly be performed in the general practice, the karyotype is probably the most interesting ancillary technique in the field of lipomatous tumors. The identification of chromosomal abnormalities in a large number of them have provided interesting insights into the relationships between various tumor types and some of these abnormalities are sufficiently (albeit not entirely) specific to play a diagnostic role in morphologically difficult cases (Table 1).
| Table 1. Cytogenetic aberrations in lipomatous soft tissue tumors | ||
| Diagnosis | Cytogenetic events | Frequency |
| Lipoma | rearrangements of 12q 13q 6p |
75% 10% 10% |
| Spindle cell / pleomorphic. lipoma | rearrangements of 16q, 13q | |
| Hibernoma | rearrangement of 11q | |
| Lipoblastoma | rearrangement of 8q | >25% |
| Atypical Lipoma / WD liposarcoma | ring chromosome 12 | >75% |
| Myxoid / round cell liposarcoma | t(12;16)(q13;p11) | >90% |
2. Tumors with a predominant adipocytic component
2.1. Ordinary lipoma
Lipoma represents by far the most common mesenchymal neoplasm.
Lipomas are rare during the first 2 decades and usually appears between 40 and 60 years. Most (but not all) lesions are superficial . They occur predominantly in the upper back or neck, abdomen, and proximal portions of the extremities and are multiple in 5 to 10% of cases.
Histologically, they are composed of mature fat cells showing only slight variations in size and shape. Nuclei are fairly uniform. Intranuclear vacuoles are commonly found and should not be regarded as evidence for lipoblastic activity.
Secondary changes are not uncommon and may cause diagnostic problems. Traumatized lesions contain foci of fat necrosis, characterized by nests of foamy macrophages distributed in the intercellular spaces or around lipocytes. These macrophages must be differentiated from lipoblasts which have hyperchromatic, usually enlarged nuclei
It is interesting to note that despite their close resemblance to normal adipose tissue, most lipomas are characterized by karyotypic abnormalities, usually involving chromosome 12.
2.2. Other lipomas
Lipomas containing a significant fibrous component are sometimes called " fibrolipoma ".
Small foci of myxoid changes are occasionnally found. In rare cases, designated as " myxolipoma ", these changes may be extensive and their rich vascularity may become clearly apparent. The transition with classical areas as well as the absence of lipoblasts and of a plexiform vascular pattern allows the distinction from myxoid liposarcoma.
Foci of cartilaginous or osseous metaplasia are other occasionnal findings.
2.3. Intramuscular lipoma
Intramuscular lipoma affects middle-aged adults, with a predilection for the thigh and trunk.
These tumors are usually poorly circumscribed and tend to extend between variably atrophic skeletal muscle fibers.
These lesions may recur in up to 20% of cases if incompletely excised.
2.4. Lipomatosis
Extermely rare condition characterized by a diffuse overgrowth of mature fatty tissue.
Different forms have been described:
- Diffuse lipomatosis affects large portions of an extremity or trunk.
- Symetric lipomatosis affects the neck and shoulders
- Pelvic lipomatosis involves the perirectal and perivesical regions and may cause urinary obstruction.
- Steroid lipomatosis.
2.5 Pleomorphic lipoma
This benign tumor forms with spindle-cell lipoma a spectrum of lesions with overlapping clinical, morphologic and cytogenetic characteristics. Both lesions are discussed below (3.2)
2.6. Lipoblastoma
Lipoblastoma is a rare benign tumor of infancy, affecting children principally before the age of 7 years. These lesions have a predilection for the limbs and are usually superficial. Deeper tumors, which tend to be larger and more infiltrative, are known as lipoblastomastosis.
Histologically, lipoblastoma is characterized by a prominent lobular architecture. Lobules, which are separated by fibrous septa, are composed of mature and immature fat cells, in variable proportions. Immature lesions, composed of primitive mesenchymal cells and lipoblasts, in a richly vascularized myxoid stroma, are virtually indistinguishable from myxoid liposarcoma.
In this differential diagnosis, the age of the patient is of greatest importance, as myxoid liposarcomas are exceedingly rare under the age of 10 years. A striking lobulation, with fibrous septa, and some maturation in the center of lobules (whereas in myxoid liposarcoma, maturation is seen in their periphery) also favor lipoblastoma. Cytogenetics may be helpful as lipoblastoma shows consistent rearrangements of chromosome 8.
2.7. Hibernoma
Rare tumor showing differentiation towards brown fat. Occurs in young adults, with a predilection for the scapular and interscapular region.
Lobulated lesion composed an admixture of mature adipocytes and cells characterized by a small, central nuclei and a finely vacuolated cytoplasm.
No recurrences are seen after excision
2.8. Atypical lipomatous tumor / Well differentiated liposarcoma (" lipoma-like " variant)
General features of liposarcoma are discussed below (4.1)
Well-differentiated liposarcoma accounts for 40 to 45% of all liposarcomas and the lipoma-like form is by far the most common of its variants.
Grossly, these tumors are usually well circumscribed, but tend to be larger and coarsely lobulated, with pale, firmer areas.
Histologically, lipoma-like liposarcoma is characterized by a variation in size of adipocytes, some of which showing atypical, hyperchromatic nuclei. Bizarre, often multinucleated stromal cells are often found in fibrous septa, or occasionnally in vessel walls. Typical lipoblasts, which are often hard to find and may be absent, are not required to the diagnosis of atypical lipomatous tumor / well differentiated liposarcoma.
Virtually all lesions, with or without lipoblasts are characterized cytogenetically by ring or long marker chromosomes derived from the q13-15 region of chromosome 12.
In the absence of a dedifferentiated component, well-differentiated liposarcoma does not metastasize and lesions that can be surgically excised (usually outside the retroperitoneum) are usually cured. For this reason, Evans et al. have introduced the term " atypical lipoma " for well-differentiated tumors of the extremities. Other authors have expanded this definition to all tumors characterized by atypical lesions lacking lipoblasts, regardless of their location, or to all superficial lesions.
In practice, both terms may probably be used interchangeably depending on the clinical setting and the degree of interaction with surgeons. We personnally use the term well-differentiated liposarcoma for retroperitoneal lesions as well as large, deep tumors causing significant morbidity or requiring agressive surgerical procedures, and reserve the term atypical lipomatous for lesions that are more easily curable (often superficial).
Regardless the term used, it must be emphasized that all of these lesions should be carefully
sampled as it is now known that even subcutaneous lesions are capable of dedifferentiation.
3. Tumors with admixed adipocytic and other connective tissue elements
3.1. Angiolipoma
These rather common lesions differ from common lipomas by the fact that they occur in young adults, are often painful and are multiple in 2/3 of cases. There is a predilection for the the forearm (2/3 of cases), arm and chest wall. Microscopically, they are defined by the presence of variable amounts of small vessels, some of which contain fibrinous microtrombi.
Lesions occuring on the chest wall must be differentiated from well differentiated angiosarcoma of the breast
3.2. Spindle cell / pleomorphic lipoma
Spindle cell / pleomorphic lipoma has a typical clinical setting: these lesions mainly affect males in their mid to late adult life and most cases are found in the back of the neck, upper back or shoulders. They are less commonly encountered more anteriorly in the head and neck region.
Clinically, they present as painless, slowly growing, superficial lesions indistinguishable from ordinary lipoma.
Histologically, spindle cell lipoma is characterized by an admixture of adipocytes and spindle cells in variable proportions; adipocytes may occasionnally be absent. Spindle cells, arranged in short fascicles, have bland, uniform nuclei and pale eosinophilic " bipolar " cytoplasm. Some nuclear palissadism may be observed. Cells are positive for CD34. The stroma is characterized by the presence of brightly eosinophilic collagen fibres and of numerous mast cells. Some cases show prominent myxoid changes.
In pleomorphic lipoma, mature adipocytes are associated with bizarre, often multinucleated cells (" floret cells ") and with a few lipoblasts.
Interestingly, spindle cell and pleomorphic lipoma share common karyotypic abnormalities (rearrangements of 13q and 16q) and most tumors show hybrid features between both of these lesions.
Spindle cell / pleomorphic lipoma does not recur.
Spindle cell lipoma must be differentiated from schwannoma and neurofibroma (negativity of spindle cells for S100). Clinical features are primordial in the differential diagnosis between atypical lipoma and pleomorphic lipoma. The relative regularity of adipocytes and the presence of " ropy " collagen also favor the latter. However, as there is some morphological overlap, tumors showing histological features of spindle cell / pleomorphic lipoma but occuring in deeper tissues or in unusual sites should be regarded with diagnostic suspicion. Pleomorphic liposarcoma appears frankly sarcomatous and usually contains " MFH "-like areas.
Practically, spindle cell / pleomorphic lipoma should always be considered in the differential diagnosis of lipomatous, spindle cell or myxoid lesions occuring in the upper back / back of the neck area.
The rare intradermal spindle cell lipoma have ill-defined margins and are more commonly locate in the face.
3.3. Hamartomas with an adipocytic component
3.3.1 Angiome intramusculaire / Angiomatoses
Adipose tissue is often present in intramuscular hemangioma. When this fatty component is particularly abundant, it may be mistaken for intramuscular lipoma. However, these lesions should be distinguished as intramuscular angioma tend to recur more often (30-50% of cases) than intramuscular lipoma (20% of cases). Clinically, the majority of intramuscular hemangiomas occur in adolescents and young adults, with a predilection for the head and neck musculature.
The term angiomatosis is used when adjacent tissues such as skin or bone are involved.
3.3.2. Angiomyolipoma
Angiomyolipoma typically occurs in the kidney, where it is the most common mesenchymal neoplasm, but occasional cases may be predominantly located in the retroperitoneum.
Angiomyolipoma is classically composed of an admixture of mature adipose tissue, smooth muscle and thick-walled vessels. It belongs (as lymphangioleiomyomatosis and " sugar tumor " of the lung) to the spectrum of tumors composed of " perivascular epithelioid cells ", characterized immunohistochemically by HMB45 positivity.
Predominantly adipocytic tumors may be easily mistaken for lipoma or liposarcoma. An extensive sampling and immunohistochemical stains (HMB45) are particularly helpful.
Angiomyolipoma is usually benign, although extremely rare monophasic epithelioid tumors may behave agressively.
Tumors may be multiple and / or bilateral in tuberous sclerosis.
3.3.3. Myelolipoma
Rare lesion usually involving the adrenal glands, although occasionnal cases have been reported in the pelvis and retroperitoneum. The tumor is composed of an admixture of mature adipocytes and hematopoietic elements. There is no association with any hematological disorder.
3.3.4 Fibrolipomatous hamartoma of nerve
Rare lesion appearing in early childhood, as a slowly growing fusiform swelling of a nerve, usually in the forearm or wrist (median nerve), associated with symptoms of compression neuropathy. Histologically, the epineurium is expanded by abundant mature fibrofatty tissue.
There is no treatment and excision inevitably leads to a neurologic deficit.
3.4. Chondroid lipoma
Chondroid lipoma is a rare fatty tumor that occurs predominantly in middle-aged adults, mostly females. Most cases are deep seated and located in the proximal extremities or limb girdles.
Histologically, chondroid lipoma is a well circumscribed lesion composed of a varying admixture of mature adipocytes and eosinophilic or vacuolated cells, arranged in cords and strands, in a myxohyaline matrix. Vacuolated cells, which contain fat and glycogen resemble chondroblasts or hibernoma cells. Some of them, characterized by multiple vacuoles and scalloped nuclei, are indistinguishable from lipoblasts.
Immunohistochemically, tumor cells are consistently positive for S100 protein. Positivity for CD68 and cytokeratins have been observed.
The differential diagnosis includes mxoid liposarcoma (characteristic vascular pattern, relatively uniform lipoblasts), extraskeletal myxoid chondrosarcoma (lobulation, absence of adipocytes and lipoblasts), chondroma (distal extremities, mature cartilage) and mixed tumor (absence of lipoblasts, foci of epithelial differentiation, positivity for keratins)
No recurrences have been observed.
3.5. Myolipoma
Rare and recently described entity occuring in adults, in abdominal and retroperitoneal locations, or in the abdominal wall. Histologically, myolipoma is composed of mature adipocytes and smooth muscle in variable proportions.
Myolipoma must be distinguished from liposarcoma with heterelogous elements, which has immature elements, and from angiomyolipoma, which also contains thick-walled vessels and is typically HMB45 positive.
Despite its often large size, myolipoma follows a benign clinical course.
4. Lipomatous tumors of which the adipocytic component may not be obvious
4.1. Well differentiated liposarcoma (other variants)
a. Liposarcoma: general features
Liposarcoma is probably the most common soft tissue sarcoma, accounting for approximately 20% of sarcomas. Most patients are adults, with a peak incidence of between 40 to 60 years. Tumors arise predominantly in the lower limbs (35-40%), retroperitoneum (15-20%) and the trunk (20%).
b. Well-differentiated liposarcoma
Well-differentiated liposarcoma is equally distributed between the limbs and retroperitoneum.
The lipoma-like and sclerosing variants are by far the most common and account together for 40 to 50% of liposarcomas. A transition between areas corresponding to different subtypes is commonly observed.
" Pure " well-differentiated liposarcoma is not capable of metastasis. However, retroperitoneal lesions are rarely completely excised and are associated with significant morbidity and mortality (Table 2).
| Table 2. Prognosis of well-differentiated liposarcoma | |||
| Recurrences | Dedifferentiation | Mortality | |
| Limbs | 35% | <5% | <10% |
| Inguinal region | 20% | 20-25% | 10-20% |
| Retroperitoneum | 50-80% | 20% | 30% |
4.1.2. Sclerosing WD Liposarcoma
Sclerosing liposarcoma is composed of collagenous fibrous tissue, containing scattered adipocytes and atypical stromal cells, which are often multinucleated. Lipoblasts are often hard to find.
Tumors showing myxoid changes must be differentiated from myxoid liposarcoma, which virtually never occurs in the retroperitoneum.
4.1.3. Inflammatory WD Liposarcoma
This rare morphologic variant is characterized histologically by nodular lymphocytic aggregates distributed in a variably cellularized stroma containing atypical, often multinucleated cells. Lipogenic areas are identified in most cases but may only represent a small proportion of the tissue analyzed.
The clinical history and the presence of atypical cells may help to exclude inflammatory conditions such as xanthogranulomatous pyelonephritis, mesenteric panniculitis, Castleman’s disease...
Inflammatory pseudotumor is composed of fascicles of myofibroblasts and lacks the atypical cells of inflammatory liposarcoma.
4.1.4. Spindle cell WD Liposarcoma
This rare and recently described variant is composed of spindle cells, arranged in short fascicles, whorls or in storiform fashion, admixed with a well-differentiated liposarcomatous component. Nuclei are hyperchromatic but show only mild atypia. Single cells may be positive for CD34.
Spindle cell liposarcoma must be differentiated from spindle cell lipoma (cytological features, eosinophilic collagen bundles), neurofibroma (S100 positivity) or DFSP (diffuse CD34 positivity).
4.1.5. Dedifferentiated Liposarcoma
Dedifferentiated liposarcoma has initially been defined by the association of well-differentiated liposarcoma (mostly lipoma-like and sclerosing subtypes) and a high-grade undifferentiated " MFH "-like component. However, this definition has recently been expanded to tumors in whom areas of low-grade liposarcoma are associated with a low-grade component resembling myxofibrosarcoma or " low-grade fibrosarcoma ".
Dedifferentiated liposarcoma occurs in late adult life, with a predilection for the retroperitoneum, followed by deep soft tissues of the extremities and the spermatic cord. Dedifferentiation may, however, rarely occur in subcutaneous tumors. Dedifferentiation mostly occurs de novo, although it may develop as a complication of a pre-existing well-differentiated liposarcoma.
A careful gross examination with adequate sampling of peripheral areas is important in order to identify dedifferentiated liposarcoma and to distinguish it from other sarcomas. The dedifferentiated component is often enucleated and the adjacent lipoma-like component may be neglected or considered as free margins. Grossly, atypical adipose tissue is often firmer and shows a coarser lobulation.
Microscopically, the interface between the well-differentiated and the dediffentiated areas is usually abrupt but there may be transitional zones or the two patterns may appear intricate.
The dedifferentiated component is variable. Most cases are composed of spindle and pleomorphic cells arranged in short fascicles, resembling so called " MFH ", although a few cases may show a low-grade morphology. Heterologous (rhabdomyosarcomatous, leiomyomatous or osteosarcomatous) element are present in approximately 10% of cases. A few cases characterized by meningeal-like micronodules with metaplastic bone have recently been reported.
Despite a high-grade morphology, dedifferentiated liposarcoma only metastasize in a relatively small proportion of cases (10-20%) which contrasts with most other sarcomas. However, the recurrence rate is high, especially in the retroperitoneum. According to Henricks et al., the behavior does not seem to be statically influenced by the amount of dedifferentiation neither by the histologic grade of the dedifferentiated component.
Because of its relatively better prognosis, dedifferentiated liposarcoma should be distinguished from other spindle cell and pleomorphic sarcomas and practically, dedifferentiated liposarcoma should be considered in the differential diagnosis of virtualy any retroperitoneal sarcoma. The identification of the well-differentitated component allows the correct diagnosis. In difficult cases, the karyotype may be helpful as the dedifferentiated component keeps the rings and markers which characterize well-differentiated liposarcoma.
The high-grade component of dedifferentiated liposarcoma must also be differentiated from pleomorphic liposarcoma, which contains lipoblasts.
4.2. Myxoid / round cell liposarcoma
Myxoid and round cell liposarcoma represent a single entity, characterized by a morphologic spectrum from pure myxoid lesions (low-grade) to pure round cell tumors (high-grade) and sharing a t(12;16) or rarely t(12;22) translocation. These tumors account for approximately 35 to 50% of liposarcomas. Clinically, myxoid liposarcoma affects adults in their 3rd to 5th decades. Most tumors are located in the limbs, with a predilection for the thigh and popliteal fossa. Myxoid liposarcoma virtually never occurs in the retroperitoneum.
Myxoid liposarcoma is usually very well circumcribed. It is composed of monomorphic, primitive fusiform or stellate cells, lacking significant nuclear atypia. The prominent meshwork of delicate, thin-walled capillaries (" crow’s feet " or " chicken wire " pattern) is highly distinctive. The presence of acellular " mucin pools " is another helpful clue. Small univacuolated lipoblasts are commonly found in subcapsular areas.
The " round cell " component represents cellular areas composed of uniform round or spindle cells with larger nuclei. Mitoses are more frequently found. The typical vascular network may be obscured in particularly cellular lesions.
Tumor cells of both myxoid and round cell components may be positive for S100 protein in approximately 30-50% of cases.
Pure myxoid liposarcoma is a low-grade tumor which only rarely metastasize. In contrast, round cell liposarcoma is a high grade lesion, with a high metastatic rate. Metastases develop in the lung but also, characteristically, in the retroperitoneum and pleural cavities, or in soft tissues.
As it is exceedingly rare in the retroperitoneum, the identification of myxoid liposarcoma in this location should prompt a careful search for a primary tumor in the limbs.
The amount of round cells (or cellular areas) necessary to classify these tumors as intermediate grade is still debated but every lesion containing more than 10% of cellular areas should be reagarded with caution in terms of prognosis.
The main differential diagnosis of myxoid liposarcoma is myxofibrosarcoma, which has thicker curvilinear vessels, and shows a greater degree of nuclear atypia (table 3). Lipoblastoma may be virtually indistinguishable from myxoid liposarcoma and practically a " myxoid liposarcoma " under the age of 5 years is actually a lipoblastoma. Extraskeletal myxoid chondrosarcoma lacks the prominent vascularity of myxoid liposarcoma. Lesions containing abundant mature adipocytes may be confused with well-differentiated liposarcoma or even myxolipoma.
Round cell liposarcoma must be differentiated with metastatic carcinoma, melanoma, lymphoma, or even Ewing’s sarcoma. The correct diagnosis is suggested by the presence of myxoid areas and by the typical plexiform vascular pattern, which can be highlighted by immunostains for CD31 or CD34. S100 protein staining may also help to identify lipoblasts.
| Table 3. Myxoid liposarcoma vs myxofibrosarcoma | ||
| Myxoid liposarcoma | Myxofibrosarcoma | |
| Age | young adults | older adults |
| Localization | deep | 70% superficial |
| Circumscription | well circumscribed, sharp borders | infiltrative |
| Vascular pattern | thin branched capillaries | thicker curvilinear vessels perivascular condensation |
| Cytologic features | small bland spindle or rounded cells | nuclear hyperchromatism |
| Mitoses | rare | common |
| Other features
|
univacuolated lipoblasts mucin pools |
" pseudolipoblasts " Inflammatory component |
4.3. Pleomorphic Liposarcoma
Pleomorphic liposarcoma is a rare tumor, accounting for approximately 5% of all liposarcomas.
Clinically, there is a predilection for the deep soft tissues of the lower limbs.
Morphologically, most cases present as a pleomorphic tumor containing scattered lipoblasts, although a few tumors contain large sheets of lipoblasts. S100 protein only stains lipoblasts.
Pleomorphic liposarcoma is an agressive tumor which must be distinguished from dedifferentiated liposarcoma.
4.4 " Malignant mesenchymoma "
The term " malignant mesenchymoma " has been applied to soft tissue sarcomas showing two or more types of differentiation (more commonly liposarcoma, rhabdomyosarcoma and osteosarcoma) other than any undifferentiated " fibrosarcomatous " or " MFH-like " components. Malignant peripheral nerve sheath tumors with heterologous elements are generally excluded.
These very uncommon lesions mainly affects patients older than 55 years and have a predilection for the retroperitoneum and the thigh. Their clinical course often seems less agressive than expected regarding to their high-grade histology.
As a liposarcomatous component is found in a large proportions of these lesions some authors have suggested that at least a majority of these tumors represent dedifferentiated liposarcoma, which might contribute to explain the clinical features shared by both lesions and the relatively good prognosis of malignant mesenchymoma.
5. Other lesions mimicking lipomatous tumors
Lobules of adipose tissue may be found in tumors showing the morphological (hemangiopericytomatous vascular pattern, " patternless pattern ", varying cellularity...) and immunohistochemical (CD34 +, CD99 +) features of solitary fibrous tumor (" lipomatous hemangiopericytoma " or " fat-forming SFT ").
Strict criteria must be applied for the identification of lipoblasts to avoid confusion with vacuolated cells found in other tumors (such as chordoma, signet-ring carcinoma...), or with vacuolated histiocytes (lipogranulomas, silicone granuloma, PVP granuloma...)
| Table 5. Lipomatous tumors: diagnostic clues | |
Diagnosis |
Comments - Diagnostic clues |
| Angiolipoma | - Fibrinous microthrombi |
| Lipoblastoma | - Before 7-8 y.o. - May be virtually indistinguishable from myxoid liposarcoma |
| Spindle cell lipoma | - CLINICAL FEATURES !!!: M 45-65, upper back / neck - hyaline collagen bundles, bland bipolar spindle cells - CD34 positive |
| Intramuscular hemangioma | - Search for vessels in benign-appearing deep-seated " lipomas " |
| Angiomyolipoma | - HMB45 positive ! |
| Atypical lipoma | - Lipoblasts are not required - Search for atypical cells in fibrous septa and vessel walls |
| Dedifferentiated liposarcoma | - Always sample the peripheral adipose tissue in " MFH-like " spindle cell / pleomorphic sarcomas, especially if located in the retroperitoneum |
| Myxoid / round cell liposarcoma | - well circumscribed !, thin branching vessels, mucin pools |
| - Lipoblasts are characterized by a scalloped, HYPERCHROMATIC, often enlarged nucleus | |
| - Immunostains for S100 protein may help to identify lipoblasts | |
| - Always consider well-differentiated liposarcoma and its variants (including dedifferentiated liposarcoma) in the differential diagnosis of retroperitoneal tumors | |
| - Consider spindle cell / pleomorphic lipoma in the differential diagnosis of lipomatous, spindle cell or myxoid tumors from the back of the neck | |
1. Beham A, Fletcher CDM. Intramuscular angioma: a clinicopathologic analysis of 74 cases. Histopathology 1991, 18, 53-9
2. Enzinger FM, Weiss SW. Soft tissue tumors, Mosby, 3rd edition 1995, 381-466
3. Evans HL et al. Heterologous elements in the dedifferentiated component of dedifferentiated liposarcoma. Am J Surg Pathol 1994, 18, 1150-7
4. Fletcher et al. Correlation between clinicopathologic features and karyotype in lipomatous tumors. Am J Pathol 1996, 148, 623-30
5. Fletcher CDM, Martin-Bates A. Intramuscular and intermuscular lipoma: neglected diagnosis. Histopathology 1988, 12, 275-87
6. Kilpatrick SE, et al. The clinicopathologic spectrum of myxoid and round cell liposarcoma. A study of 95 cases. Cancer 1996, 15, 1450-8.
7. Kindblom LG, Meis-Kindblom JM. Chondroid lipoma: an ultrastructural and immunohistochemical analysis with further observations regarding its differentiation. Human Pathol 1995, 26, 706-15
8. Kraus MD, Guillou L, Fletcher CDM. Well-differentiated inflammatory liposarcoma: an uncommon and easily overlooked variant of a common sarcoma. Am J Surg Pathol 1997, 21, 518-27
9. Meis JM, Enzinger FM. Chondroid lipoma. A unique tumor simulating liposarcoma and myxoid chondrosarcoma. Am J Surg Pathol 1993, 17, 1103-12
10. Mentzel T, Bosenberg MB, Fletcher CDM. Pleomorphic liposarcoma: clinicopathologic analysis of 31 cases. Mod Pathol 1999, 12 (abstract)
11. Mentzel T, Calonje E, Fletcher CDM. Lipoblastoma and lipoblastomatosis: a clinicopathologic study of 14 cases. Histopathology 1993, 23, 527-33
12. Mentzel T, Fletcher CDM. Lipomatous tumours of soft tissues: an update. Vrichows Arch 1995, 427, 353-63
13. Nascimento AG et al. Dedifferentiated liposarcoma. A report of nine cases with a peculiar neurallike whorling pattern associated with metaplastic bone formation. Am J Surg Pathol 1998, 22, 945-55
14. Rao VK, Weiss SW. Angiomatosis of soft tissue. An analysis of the histologic features and clinical outcome in 51 cases. Am J Surg Pathol 1992, 16, 764-71
15. Rubin BP, Fletcher CDM. The cytogenetics of lipomatous tumours. Histopathology 1997, 30, 507-11
16. Smith TA, et al. Myxoid/round cell liposarcoma of the extremities. A clinicopathologic study of 29 cases with particular attention to extent of round cell liposarcoma. Am J Surg Pathol. 1996, 20,171-80
17. Tallini G, et al. Combined morphologic and karyotypic study of 28 myxoid liposarcomas. Implications for a revised morphologic typing, (a report from the CHAMP Group). Am J Surg Pathol 1996, 20, 1047-55
18. Weiss SW, Rao VK. Well differentiated liposarcoma (atypical lipoma) of deep soft tissue of the extremities, retroperitoneum and miscellaneous sites. A follow-up study of 92 cases with analysis of the incidence of " dedifferentiation ". Am J Surg Pathol 1992, 16, 1051-8
| homepage | part I | part II | part III |
Copyright 2000, The Author(s) and/or The Publisher(s)
| Organisation: FORPATH asbl  |
Coordination: Dr Bernard Van den Heule |
Host: Labo CMP |