Connective tissue tumors

Chapter 35 Connective tissue tumors






TUMORS OF FIBROUS AND MYOFIBROBLASTIC TISSUE 1604













TUMORS OF VASCULAR ORIGIN 1705










Introduction


Connective tissue tumors presenting primarily in the skin are relatively common. Because the majority of such lesions are benign and clinically nondistinctive they are sometimes neglected by clinicians. However, histologically they constitute a complex group of tumors showing various lines of differentiation and it is often difficult to classify a lesion as benign or malignant. Also, cutaneous or subcutaneous sarcomas, as well as various neoplasms of intermediate malignancy, are seen sufficiently frequently that some knowledge of their behavior and pathological appearances is mandatory for dermatologists and dermatopathologists alike.


Many benign soft tissue lesions – lipoma and fibrous histiocytoma being the most common – are often slow growing and asymptomatic. As a result, they frequently remain untreated unless they are a cosmetic nuisance, and so an accurate estimation of their incidence (which is probably relatively high) is impossible. However, sarcomas are relatively rare at any site, accounting for less than 1% of all malignant neoplasms.


In this chapter, emphasis is placed upon those lesions that commonly present in the skin; various nondermatological conditions are included for the sake of completeness and because they may be seen, albeit very occasionally, in dermatopathological practice.


When dealing with any soft tissue neoplasm, the single most important dictum to be strictly followed is that adequate tissue sampling, surgically and pathologically, is essential for accurate diagnosis. The range of diagnostic and non-specific histological appearances seen in these tumors is very wide, reflecting the multipotentiality of mesenchyme; only by obtaining an overall view of a given neoplasm can a reliable diagnosis be made. In this regard, punch and shave biopsies are almost guaranteed to give rise to diagnostic errors.


A number of cutaneous mesenchymal tumors have genetic features that can be helpful diagnostically. In general, malignant soft tissue tumors fall into the class of complex karyotype sarcomas (for example, angiosarcoma and leiomyosarcoma) or simple genetic profile (for example, clear cell sarcoma or dermatofibrosarcoma) often associated with a chromosomal translocation or, less often, with mutation or loss of a specific gene. An exhaustive discussion of the molecular diagnostics of soft tissue tumors is beyond the scope of this chapter, but see Chapter 2 for additional discussion of relevant techniques. Most of the molecular features discussed in this present chapter can be used diagnostically when required, although some of the tests are available only in specialized centers.



ADIPOCYTIC TUMORS



Benign adipocytic tumors



Lipoma



Clinical features


Lipomas are the most common connective tissue tumors.13 They appear to occur more frequently in the obese, usually in middle and late adult life, may be multiple and are purportedly more common in females. This, however, may only be a reflection of the greater tendency of women to request cosmetic attention for otherwise innocuous lesions. Lipomas are very uncommon in children and when present should raise the possibility of Bannayan-Riley-Ruvalcaba syndrome.4 Congenital lipomas are very rare.5 Multiple lesions may occur in a familial setting.6 A case of multiple lipomas after total body electron beam therapy for mycosis fungoides has been reported.7 Multiple lipomas have also been described in association with rosiglitazone, a peroxisome proliferator-activator receptor (PPAR) gamma agonist, in association with systemic chemotherapy for Hodgkin’s lymphoma and in Cowden’s disease.810


The lesions are found most often on the trunk, abdomen or neck, followed by the proximal extremities, and rarely on the face (particularly the forehead), scalp, hands or feet. Palmar lipomas are exceptional and may present with lesions simulating piezogenic pedal papules.11 Periungual and subungual lesions are exceptional.12,13 Trauma has been associated with induction of lipomas although it is not clear whether all of these lesions may represent pseudolipomas.14,15 The latter sometimes includes an intravascular lesion.16 Typically, they originate subcutaneously, are slow growing, mobile and painless; sometimes they are multiple. Size varies and some lesions are very large. Dermal examples are often clinically confused with fibroepithelial polyps. Although the lesions are usually well circumscribed, the less common deep variants, which may arise in muscle or in association with a tendon sheath or nerve, are generally ill defined and infiltrative.


Subcutaneous lipomas are entirely benign and local excision is nearly always curative; recurrence is infrequent and progression to liposarcoma almost never occurs.



Pathogenesis and histological features


Lipomas at all locations show clonal karyotypic abnormalities in up to 75% of cases.1720 The most common rearrangement in the 12q13~15 region and the HMGA2 gene most often with LLP at 3q27~28, though other loci are described.1722


The tumors are usually encapsulated, lobulated and largely composed of univacuolated mature adipocytes, the nucleus and cytoplasm of which are compressed centrifugally (Fig. 35.1). The lobules are divided by delicate fibrous septa containing thin-walled vessels. Degenerative changes, often characterized by fibrosis, focal fat necrosis or myxoid change, are not uncommon, particularly in long-standing or frequently traumatized cases (Figs 35.235.00150). Prominent myxoid change and high vascularity are sometime present.23 Foci of other fully differentiated mesenchymal elements, including bone or cartilage, may also be seen.









Although nuclear pleomorphism, hyperchromasia and mitotic activity do not occur in lipomas, in any benign fatty lesion (or even in normal adipose tissue) occasional vacuolated nuclei known as lochkern may be seen (Fig. 35.8). These must not be confused with lipoblasts, the most important diagnostic feature of liposarcoma, which are characterized by multiple intracytoplasmic lipid vacuoles associated with scalloping of peripherally located hyperchromatic or bizarre nuclei. In some lesions there are septa of collagen between adipose tissue lobules and they are referred to as fibrolipomas. A variant of lipoma with predilection for acral sites (fingers, wrists, toes) and characterized by prominent collagenous or myxocollagenous stroma, bland stellate or spindle-shaped cells and scattered adipocytes has been described as sclerotic (fibroma-like) lipoma.24 A further variant known as fibrohistiocytic lipoma has been reported and this is described below.25 Rare lipomas may contain bone.26 Those containing sweat glands do not represent an adenolipoma but rather entrapment of normal glands by the tumor.2729 Lesions containing smooth muscle are rare; they have been described as myolipomas and tend to be deep seated.30 Focal areas of fat necrosis with foamy histiocytes are often seen and some cases show membranous fat necrosis.31



Dermal lipomas are less well circumscribed and consist of scattered groups of mature adipocytes between collagen bundles (Figs. 35.9, 35.10).






Angiolipoma





Differential diagnosis


Cellular angiolipoma can be confused with a vascular tumor, especially immature capillary hemangioma and kaposiform hemangioendothelioma.16 The presence of mature adipocytes and capillaries with microthrombi allows distinction from immature capillary hemangioma. Kaposiform hemangioendothelioma may have capillaries with microthrombi in the periphery of tumor lobules, but mature adipocytes are absent.



Spindle cell lipoma



Clinical features


Spindle cell lipoma is a comparatively uncommon variant and may be a source of histological concern to the unwary.13 Found predominantly in males, they arise mainly in the posterior portion of the neck, shoulder or upper back, and are characteristically seen in the sixth or seventh decade. Multiple lesions are rare and some are familial.4,5 Rare cases can occur at other locations including the foot, oral cavity (including the tongue), larynx, orbit, soft tissues of the perianal area, aortic valve, mediastinum and breast.616 The last may represent an example of mammary-type myofibroblastoma of soft tissue, a lesion closely related to spindle cell lipoma.17 They usually occur as a well-circumscribed, slowly growing, solitary, subcutaneous or (rarely, in up to 13% of cases) dermal lesion, less than 5 cm in diameter.1820 The last appear most commonly on the face and are more common in females. Intramuscular presentation is very rare.2124, A case has been reported at the site of an infantile fibrosarcoma treated with chemotherapy.25 Spindle cell lipoma is an entirely benign, nonrecurring lesion.



Pathogenesis and histological features


A number of chromosomal abnormalities have been found in spindle cell lipoma, identical to those found in pleomorphic lipoma. Monosomy or partial loss of chromosomes 13 and 16 are the most common alterations also seen in pleomorphic lipoma, strongly suggesting that these two lesions exist as a morphologic continuum.2629 Interestingly, similar loss of 13q has been found in mammary-type myofibroblastoma and cellular angiofibroma, suggesting a close link between these tumors.18,30,31


Subcutaneous lesions tend to be well circumscribed and dermal tumors are ill defined.20 In addition to mature univacuolated adipocytes, irregular collections of slender spindled cells are seen with pale eosinophilic cytoplasm, uniform nuclei and rare mitoses (Fig. 35.15). Hyaline bundles of collagen and occasional giant cells may also be present, but lipoblasts are rarely identified. Mast cells are often numerous (Fig. 35.16). The relative proportions of adipose tissue to spindled cells vary between individual cases (Fig. 35.17). Some cases contain few or, rarely, no adipocytes at all.32 Vascularity also varies and focal hemangiopericytoma-like areas are sometimes seen. Extensive myxoid change can lead to striking degenerative features with a pseudovascular pattern in which papillary structures project into empty spaces (Fig. 35.18).33 However, it has been shown that at least in some examples showing this change, the spaces are truly lined by endothelial cells, and these should be named angiomatous spindle cell lipoma.34






The spindled cells are positive for CD34 but negative for S-100. Only mature adipocytes are positive for S-100.


Ultrastructural studies show cells with features of mature adipocytes and spindled cells representing undifferentiated mesenchymal cells.33




Mammary-type myofibroblastoma of soft tissue



Clinical features


This is a rare tumor identical to myofibroblastoma that occurs in the breast.1 As with the latter tumor, it is most common in adult males and presents as an asymptomatic slowly growing subcutaneous mass with predilection for the groin/inguinal area. Size varies but tends to be less than 2 cm. Lesions can also rarely occur on the trunk, vaginal wall, paratesticular area, vulva, perianal area and lower limb.15 There seems to be a predilection for tumors to occur along the milk line. Simple excision is the treatment of choice and there is no tendency for local recurrence.



Pathogenesis and histological features


Mammary-type myofibroblastoma appears to be part of a morphologic spectrum that includes cellular angiofibroma and spindle cell lipoma. It has been suggested that the histological variations probably depend on anatomic location.6


Tumors are well-circumscribed and composed of a mixture of bland spindled cells and variable, sometimes prominent, amounts of mature adipose tissue.1 The spindled cells are arranged in fascicles and display a myofibroblast-like appearance with tapering nuclei and amphophilic cytoplasm with an indistinct cytoplasmic membrane. Cytologic atypia is rare and mitotic figures are exceptional. Epithelioid cells may rarely be seen and sometimes scattered multinucleate cells can be identified. Blood vessels are small and tend to be inconspicuous. The stroma is often myxoid, mast cells are common and hyalinized collagen bundles are intermixed with tumor cells.


Immunohistochemistry shows positivity for CD34 and desmin and focal positivity for actin and calponin in a number of cases.1


Cytogenetic analysis has shown partial monosomy of chromosomes 13q and 16q, further emphasizing the relationship with spindle cell lipoma, a tumor with similar cytogenetic abnormalities.7



Pleomorphic lipoma




Pathogenesis and histological features


Cytogenetic abnormalities are the same in pleomorphic lipoma and spindle cell lipoma, confirming that they are part of the same spectrum (see above).4,5 In addition to the histological features of spindle cell lipoma, pleomorphic lipoma is characterized by numerous hyperchromatic and irregular multinucleated giant cells, with nuclei often arranged in a concentric floret pattern (floret giant cells) (Figs 35.1935.21). Floret-like cells may also be seen in prolapsed orbital fat as a result of a degenerative process.6 Mitotic figures may rarely be evident and occasional multivacuolated lipoblasts are sometimes present (Fig. 35.22). Lesions that show few or no adipocytes may pose a diagnostic challenge.7







Chondroid lipoma



Clinical features


Chondroid lipoma is a distinctive tumor that presents predominantly in adult females, with a predilection for the proximal extremities and limb girdles.1 Tumors in children are very rare.2 Lesions are usually small and arise mainly in deeper soft tissues and (less commonly) in the subcutis. Rare examples present in the oral cavity, nasopharynx and pelvis.35 Clinical features are not distinctive. Tumors are benign and there is no tendency for recurrence after simple excision.





Lipomatosis



Clinical features


Lipomatosis is extremely rare and may present in several forms, two of which affect the superficial subcutaneous tissue:14


Multiple symmetric lipomatosis (Launois-Bensaude) represents the commonest form and can be diffuse or localized.13,5 In the diffuse variant, there is usually symmetrical involvement of the trunk or proximal limbs and occasionally the abdominal cavity;4 it is seen most often in children (particularly males). Some cases show an autosomal dominant inheritance, others are associated with myoclonic epilepsy with ragged red fibers (MERRF), and a number may be associated with diabetes mellitus.69 The localized variant is characteristically seen in the cervical region, usually in middle-aged males, and is known as Madelung’s disease. In the latter, inspiratory dyspnea or obstructive sleep apnea may exceptionally occur.10,11 The axillae and groins may also be affected. There is a strong association with alcohol abuse and liver disease.12 A variant of localized symmetrical lipomatosis restricted to the hands or the feet has been reported.13,14

Asymmetric lipomatosis can present at any site and usually has no association with other diseases.15 Single reports of associations with familial hyperlipidemia and tuberous sclerosis have been documented.16,17

A localized form of lipomatosis of the scalp has been reported as encephalocraniocutaneous lipomatosis and is associated with alopecia and ocular and cranial abnormalities.18,19


Congenital facial infiltrating lipomatosis refers to a disorder associated with hypertrophy of bones and soft tissues, macrodontia and premature dental eruption.20,21


In both forms of lipomatosis, only radical surgery can prevent local recurrence. The disadvantages of recommending such treatment must be weighed against the possible functional impairment that the condition may induce.




Adiposis dolorosa



Clinical features


Adiposis dolorosa (Dercum’s disease) is a rare disease characterized by painful, circumscribed areas with increased fat in a plaque-like distribution.13 Usually, multiple body sites are involved but there is predilection for the buttocks, lower limbs and abdomen, particularly in juxta-articular areas. Localized disease is very rare and the breasts may be involved.4,5 The condition is much more common in females, especially after the menopause, and patients often have associated obesity and psychological problems.13 Occasional cases are inherited in an autosomal dominant manner.6,7 A case associated with the use of corticosteroids and a further patient with hypercholesterolemia and severe atherosclerosis have been documented.8,9 Pain occurs mainly as the result of palpation but may also occur spontaneously or as a result of movement.




Nevus lipomatosus superficialis (Hoffman and Zurhelle)



Clinical features


Nevus lipomatosus superficialis is an uncommon form of connective tissue nevus, manifest principally by the deposition of fatty tissue in the dermis.14 In its classical form, it is characterized by multiple papular, polypoid or plaque-like lesions, up to 2 cm in diameter, which almost always arise unilaterally on the posterior surfaces of the buttocks, upper thighs or lower back. More extensive and diffuse involvement may occur and patients present with prominent folds in what has been described as the Michelin tire appearance.57 Typically, the lesions present in early childhood or adolescence. Unusual associations include co-occurrence with lipedematous scalp, folliculosebaceous cystic hamartoma, dermoid cysts and angiokeratoma of Fordyce.811 A solitary form, usually seen in adults, shows a predilection for the same sites or occurs elsewhere and is more likely to represent a variant of fibroepithelial polyp or skin tag (Figs 35.25, 35.26). Such lesions have been described as pedunculated lipofibroma.12 In all types of nevus lipomatosus the sex incidence is equal. The papules or plaques, varying from skin-colored to yellow, are characteristically broad based and may show superficial comedone formation.






Piezogenic pedal papules



Clinical features


Piezogenic pedal papules characteristically present as multiple skin-colored papules on the heels (Fig. 35.28).13 They show predilection for the internal aspect of the heels and are usually asymptomatic although pain may be elicited when the patient is standing. Lesions become more noticeable when the patient stands up as a result of pressure. Piezogenic pedal papules are common in patients with Ehlers-Danlos syndrome.4 They have been described in athletes, including a marathon runner, and in association with Prader-Willi syndrome.57 Rare familial cases have been described.8




Pathogenesis and histological features


It is likely that trauma plays a role in the pathogenesis of the lesions.5,6 A biopsy from a papule shows normal adipose tissue herniating into the dermis. This may mimic an intradermal lipoma but the clinical setting allows a diagnosis to be made.



Lipomatosis of nerve



Clinical features


Lipomatosis of nerve (fibrolipomatous hamartoma of nerve, perineural fibrolipoma, perineural lipoma, intraneural lipoma) is a very rare hamartomatous condition usually occurring in children or young adults of either sex, around the wrists and hands, particularly along the distribution of the median nerve followed by the ulnar nerve and (less frequently) others including the brachial plexus and cranial nerves.15 Presentation at birth is sometimes seen. It can be associated with macrodactyly of the fingers innervated by the involved nerve in up to one-third of cases.1,6 Patients typically present with a slowly growing mass, which is either asymptomatic or associated with neurological symptoms including pain, paresthesia, loss of sensation or motor deficit. Carpal tunnel syndrome may develop when the median nerve is involved.7,8 Although the lesion is benign, treatment is difficult, as surgical excision often results in permanent neurological deficit.




Lipoblastoma



Clinical features


Lipoblastoma is the circumscribed subcutaneous counterpart of lipoma seen in infancy and childhood.16 Its diffuse form, lipoblastomatosis, is infiltrative and typically involves deeper structures, including muscle.


In either form, this condition most often presents in the first 9 years of life (exceptionally at birth, and 10% between the ages of 10 and 16), affects males rather more than females, and is typified by a slowly growing, usually subcutaneous mass with size ranging from 1 to 15 cm.17 Most tumors involve the trunk and extremities, followed by the head and neck.7,8 Presentation in the retroperitoneum, mediastinum and a number of internal organs including the kidney occurs rarely.914 Intrascrotal tumors and association with accessory scrota have also been documented.1517 In the infiltrative type, local recurrence can occur following incomplete excision in up to 19% of cases.3 Familial cases may be seen.7 In about 17% of patients central nervous system anomalies are noted including macrocephaly, developmental delay, autism, Sturge-Weber syndrome and seizures.7 Unusual associations include a patient with glomuvenous malformations, epidermal nevus, temporal alopecia and heterochromia in addition to a lipoblastoma.18


A small series of adipose tumors closely resembling lipoblastoma and presenting in the vulva of young to middle-aged patients has been described as lipoblastoma-like tumor of the vulva.19


One or more recurrences may occur in up to 46% of cases.7


Jul 23, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Connective tissue tumors
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