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This tumor is composed of mature fat, which may be solitary or multiple, superficial or deep. Variants of lipoma include angiolipoma, myolipoma, chondroid lipoma, spindle cell lipoma and pleomorphic lipoma.66, 67 Kim YH et al., 68 studied11 benign lipogenic tumors and considered that the small spindle cells accompanying capillaries are the potential precursors of adipocytes.
It occurs most commonly between 40 and 60 years with male predilection. It is most commonly seen in the region of upper back and neck. Obese and diabetic patients have been noted to have a higher occurrence. Trauma and radiation has also been implicated. Macroscopically, it is a well-circumscribed, lobulated mass. Microscopy reveals mature adipocytes admixed with variable amount of other tissue types.
These are benign neoplasms of the kidney composed of fat, smooth muscle and thick walled blood vessels in varying proportions.
This is a tumor of infancy.11 Macroscopically, they measure less than 5cm in diameter. Microscopically, the tumor is composed of mature and immature fat cells arranged in lobules. Local recurrence following excision is infrequent.
It is a rare condition, characterized by diffuse over growth of fatty tissue, which affects mainly adult males in one of the four following forms.11
-Multiple symmetric lipomatosis
Lipomatosis of nerve
It is a rare condition, characterized by the development of a slowly growing fusiform swelling, most often of the median nerve accompanied by symptoms of a compression neuropathy.11Histologically, the epineurium of the affected nerve is expanded by mature fibro fatty tissue
II. Intermediate (locally aggressive)
This may be lipoma like but for the presence of scattered multivacuolated lipoblast. The tumor has a lobulated, yellow to white, soft to firm cut surface that varies in relation to its adipocytic, fibrous, and myxoid areas. Microscopically, the tumor is composed largely of cells with lipoma-like features except for the presence of scattered hyperchromatic, often multinucleated and vacuolated cells with features of atypical lipoblasts.
Four histological subtypes are designated, namely adipocytic (lipoma-like), sclerosing, inflammatory, and spindle cell types, but more than one morphologic pattern may be present in the same neoplasm. The inflammatory variant of well-differentiated liposarcoma shows prominent lymphoplasmocytic infiltrate.69The Sclerosing variant will have alternating lipomatous and collagenous areas.
III. Malignant tumors of adipose tissue
These tumors are one of the commonest soft tissue sarcomas of adult life. It occurs most commonly between 40 and 60 years, although rare in childhood.70 It has a marked predilection for lower extremity followed by retro peritoneum. Radio graphically, liposarcoma shows distinct translucency and myxoid type stands out by increased density.
CT and MRI are valuable for detection of recurrent neoplasms.71 On gross examination, most of them measure between 5 and 10 mm, well circumscribed and yellowish on cut section
This tumor consists of lipoblasts in varying stages- from primitive mesenchymal stellate cells, multivacuolated lipoblasts to signet ring lipoblasts. These tumor cells are admixed with plexiform capillary network and abundant myxoid matrix.26
Round cell Liposarcoma
This tumor consists of poorly differentiated myxoid liposarcomatous areas with excessive proliferation of small uniform round cells.
This tumor consists of well-differentiated and poorly differentiated non lipogenic areas.
This tumor reveals large giant cells or numerous giant cells. Recurrence is common in deep-seated liposarcomas. Dedifferentiation is seen in tumors at all sites with majority in the retroperitoneum.
SMOOTH MUSCLE TUMORS
I. Benign tumors
These occur as cutaneous nodules over the extremities in the early adult life. Microscopy shows bundles of smooth muscles blending with dermal collagen.
It occurs as a painful solitary nodule, common in 4th to 6th decades of life, with predominance in females over the lower extremities.72
II. Malignant tumors
It accounts for 5-10% of all soft tissue sarcomas seen in elderly females. Commonest site is retro peritoneum. Radiation exposure is a possible etiological factor. On gross examination, the tumor appears as a fleshy large mass.
Microscopy reveals well-differentiated tumor cells arranged in fascicular pattern. The individual cells are elongated with abundant eosinophilic cytoplasm and centrally located cigar shaped nuclei. Retroperitoneal leiomyosarcomas are highly aggressive. Superficial variety has favourable prognosis if a wide excision is done.
Stout AP et al., 16 studied superficial soft tissue leiomyosarcoma and observed that more superficial tumors tend to be smaller and had a better prognosis. Wile AG et al., 73 studied 28 cases of leiomyosarcoma and found that large sized deep-seated tumors had a bad prognosis.
In 1977, Ramchod M74 studied 100 cases of GI Tract and retroperitoneal leiomyosarcomas and found frequency of mitosis as the most useful criteria for the diagnosis of leiomyosarcoma.
SKELETAL MUSCLE TUMORS
I. Benign (Rhabdomyoma)
In contrast to other soft tissue tumors, benign skeletal muscle tumors are considerably less common forming only 2% of all skeletal muscle fibres.1
The adult rhabdomyoma occurs in the head and neck area. Microscopically, lobules of large uniform polygonal cells with abundant granular, vacuolated, or eosinophilic cytoplasm; well-defined cell borders; and round nuclei with a prominent nucleolus are present.
The fetal type occurs in both adults and children The tumor forms a nodule in the subcutis or deeper soft tissues that has a circumscribed non infiltrative pattern and is composed of bundles of fetal myotubes with interspersed small immature-appearing mesenchymal cells.
The genital type occurs in the vagina and vulva of middle-aged women. Microscopically, bland, interlacing, haphazardly arranged rounded to strap-like cells that have abundant eosinophilic cytoplasm with cross-striations, cytoplasmic glycogen, and a centrally located round nucleus with a prominent nucleolus are present. The tumor cells are embedded in a fibrous stroma with dilated vessels.
II. Malignant tumors
There are classified into 3 histological types:
a) Embryonal rhabdomyosarcoma
b) Alveolar rhabdomyosarcoma
c) Pleomorphic rhabdomyosarcoma
Clinical presentation according to the histological type:
50-60% of RMS
Birth - 15 yrs75,76
15-20% of RMS
Head, neck and genitourinary
<5% of RMS
< 40 years78
Large muscles of extremities
On gross, they appear as grey white mass measuring less than 4cm.
Microscopic findings in embryonal RMS reveals a mixture of undifferentiated hyper chromatic round or spindle cells to differentiated cells having eosinophilic cytoplasm characteristic of rhabdomyoblasts and myxoid matrix.
Microscopic findings in alveolar RMS reveals ill-defined aggregates of poorly differentiated round or oval cells with central loss of cohesion and viable cells adhering to fibrovascular septa creating an alveolar pattern.
A multinucleated giant cell with peripherally placed nuclei is a characteristic and diagnostically useful feature. Pleomorphic RMS is difficult to distinguish from other pleomorphic sarcomas. Immunohistochemistry is helpful since they show positivity for desmin and myoglobin.78
The inter group rhabdomyosarcoma studies (IRS) has formed a clinical staging system. They also defined various favourable and unfavorable factors in predicting the prognosis.79
TUMORS OF BLOOD VESSEL
I. Benign tumors
These are benign but non-reactive process in which there is an increase in the number of normal or abnormal appearing blood vessels.80, 81 It is one of the common soft tissue tumors. In Geetha Dev et al., study they formed 21.3% of all benign soft tissue tumors. These are most commonly seen in infancy and childhood.82
It is the most common type consisting of capillary sized blood vessels. Cellular hemangiomas or strawberry nevus is an immature form of capillary haemangioma occurring in infancy at a rate of about 1 in every 20 live births.81
These are less frequent and are composed of dilated blood filled vessels lined by flattened epithelium.
It is a rare lesion seen in mid adult life with female predilection. Common location is around the ear.
They arise from sequestration of lymphatic tissue. There are divided into 3 types depending on the calibre of the vessels
c) Cystic hygroma
They form 0.9% of all benign soft tissue tumors in Kransdorf's series and are present at birth or by 2nd year of life with equal sex occurrence. They have predilection for head, neck and axilla.
Macroscopically, they are ill-defined sponge like lesions. Microscopy reveals lymphatic vessels lined by endothelium and filled with proteinaceous fluid containing lymphocytes. Though benign, may cause morbidity because of large size and infection. Complete excision is the preferred mode of treatment.83
These are polypoid or of capillary hemangiomas with granulation tissue and have a predilection for lips.
II. Intermediate (locally aggressive)
This is a very rare neoplasm affecting mainly infants and children, arising mainly in the retro peritoneum or the skin. These lesions may be associated with consumption coagulapathy (kasabach - Merritt syndrome). These are lobulated vascular proliferations composed mainly of spindle shaped endothelial cells.
III. Intermediate (rarely metastasizing)
These lesions occur most often in distal extremities of young adults. It is characterized by elongated vascular channels lined by hobnail endothelium with prominent lymphocytic infiltrate. These tumors often recur locally and rarely metastasize
Papillary intralymphatic angioendothelioma
This is a rare tumor seen usually in children, located in skin and soft tissues.
Microscopically, it is characterized by papillary tufts that are lined by plump endothelial cells located within the dilated vascular lumina.The tumor cells have epithelioid features with eosinophilic cytoplasm.84 This tumor has good prognosis, although nodal metastasis have occurred in a few cases.
This vascular neoplasm shows various combinations of benign, low-grade malignant and malignant components most often consisting of retiform haemangioendothelioma and epithelioid haemangioendothelioma. This tumor is common in the distal extremities and often recur locally but rarely metastasize.
These are rare tumors with four clinical settings.
The chronic type occurring in elderly males, often associated with a second malignancy of lymph reticular system.86
b) Lymphadenophathic type occur in young African children
c) Transplantation associated
d) AIDS related Kaposi sarcoma87
Microscopy reveals network of jagged blood vessels in the upper dermis with bland appearing lining cells.
IV. Malignant vascular tumor
These are malignant tumors and are the rarest soft tissue tumors. They comprise less than 1% of sarcomas.88 They formed 2.1% in Kransdorf's (1995) series, chronic lymph edema, chronic filariasis, radiation exposure and environmental chemical carcinogens are the known predisposing factors.89, 90 This tumor primarily affects elderly patients with a male predilection and occurs commonly in superficial soft tissue of the distal extremities, head and neck.91
Microscopy reveals vascular channels of irregular size and shape. Plump endothelial cells having hyperchromatic nucleus line these channels. The prognosis is poor. The tumor spreads by local extension. Commonest site of metastasis are cervical lymph nodes, lung, liver and spleen. Radical excision is to be done to prevent local recurrences.92
Tumors in this category show evidence of myoid/contractile perivascular cell differentiation. Morphologically, they have a tendency to grow in a circumferential perivascular pattern.
This tumor originates in the neuromyoarterial glomus. The classical location of this tumor is the subungual region but it can also occur elsewhere in the skin and soft tissues.11 These tumors are supplied by numerous nerve fibres and are very painful.
Microscopically, glomus tumors consist of blood vessels lined by normal endothelial cells and surrounded by a solid proliferation of epithelioid cells. On rare occasions, glomus tumors behave in an aggressive fashion, with local recurrences and invasion into adjacent structures.
Previously interpreted as a hemangiopericytoma, usually arises in the subcutis of the distal extremities. Less than 2 cm in greatest dimension, this tumor is unencapsulated but well circumscribed.
Microscopically, the tumor is composed of a densely cellular population of oval to spindle-shaped cells with eosinophilic to amphophilic cytoplasm arranged in multilayered concentric profiles around compressed blood vessels.
Malignant glomus tumor
Glomangiosarcoma is rare and seemingly arises from a benign-appearing glomus tumor. The characteristic findings are a visceral or subfascial origin, a size >2 cm, marked nuclear atypia, and atypical mitotic figures.
TUMORS OF UNCERTAIN DIFFERENTIATION
This tumor shows predilection for the pelvi perineal region of women in second or third decade of life. On gross examination, the tumor appears edematous and ill defined.11
Microscopically, a hypocellular stroma devoid of atypicality or mitotic activity is seen intermingling with vessels having dilated Lumina. No more than 30% of these lesions recur locally and the majority of such recurrences are cured by further re-excision.
Occurs primarily in adults between 40 and 60 years old as a solitary, painless, slowly growing intramuscular mass arising in the thigh, buttocks, or limb girdle. Most tumors are about 5 cm in maximal dimension, and are well circumscribed with a pale gelatinous or myxoid cut surface.
The tumor cells are small, bland, stellate to spindle in shape, have a very low mitotic rate, and are present in an abundant myxoid matrix that contains an inconspicuous vascular network
II. Malignant tumors
Alveolar soft part sarcoma
It is an uncommon neoplasm forming only 0.5% of soft tissue sarcomas in Kransdorf's et al, series (1995). 38 They are commonly seen in adolescents and young adults, with a female preponderance. The common sites are the lower extremities, especially the anterior portion of thigh.
On gross, these are poorly circumscribed, soft and friable. Cut section shows areas of necrosis and hemorrhage.93
Microscopy shows dense fibrous trabeculae dividing the tumor into compact groups that in turn are subdivided into sharply defined nests of rounded or polygonal cells having abundant granular cytoplasm giving rise to an organoid pattern.14
It has poor prognosis with likelihood of metastasis to lung or brain.94
These tumors are one of the most common soft tissue sarcomas forming 5.3% of soft tissue sarcomas in Kransdorf's (1995) series. 38 These are more common in adolescents and young adults with male predilection.95 Trauma has been implicated as a causative factor. They occur predominantly in the extremities, in the vicinity of large joints and frequently in retro peritoneum.96, 97, 98
Radio graphically, they are seen as a swelling in the vicinity of joints with 15-20% showing small spotty opacities caused due focal calcification.10
Grossly, they tend to be well circumscribed and multilobular.
Microscopy reveals two morphologically different types of cells that form a characteristic biphasic pattern. The epithelial cells and spindle cells with areas of hyalinization, calcification and myxoid changes are noted.
The epithelial cell secretions show positivity for PAS and alcian blue.
Both the cells show positivity for EMA and keratin. Vimentin is positive in spindle cells. The rate of recurrence is high and metastasis is seen in half of the cases principally to the lungs.99
Hence radical excision and adjunct radiotherapy is advocated
Clear cell sarcoma
It can produce melanin but differs from conventional melanoma in that it is more deeply located in association with tendons or aponeurosis and lacks epidermal / junctional changes. They mainly affect young adults between 20 and 40 years with female predilection and occur in the extremities.
On gross examination, the tumor appears as well circumscribed grey or white mass.
Microscopically, tumor cells, which are fusiform or cuboidal in shape, are arranged in nests and fascicles. The cells have large nucleoli with cytoplasmic melanin. Prognosis is poor and may develop local recurrences and metastasis.100
Extra skeletal Ewing's sarcoma
These are primitive neuroblastic tumors arising outside the autonomous nervous system and have good prognosis. It is more common in females around 20 years of age, commonly located in Para vertebral and chest wall region.101, 102They are lobulated masses measuring less than 10cm.
Microscopy, the tumor is composed of uniform round cells with clear to finely vacuolated cytoplasm that surrounds a central nucleus that has fine to slightly coarse chromatin. Mitotic figures are present but are not especially numerous in most cases. Architecturally, broad sheets, lobules, nests, and strands are some of the growth patterns are seen.
Other features include Homer-Wright rosettes, condensed small cellular nodules within otherwise monotonous sheets of round cells, some spindling (possibly an artifact), and a pale mucoid background.reveals sheets of small dark cells having scant cytoplasm with rosettes.103