Mesenchymal tumors

Fat + spindle cells in variable proportion, no lipoblasts. Nuclear palisading may be sometimes present. CD34 is positive.

Tumor of the blood vessels of capillary calibre (no elastic fibres nor smooth muscle within the wall, size is variable) and undifferentiated endothelia. The tumor has no capsule,its borders are unsharp. Superficial form often regress. Larger tumors, which have deep parts, do not regress and grow together with the patient.

Large, cavernous vascular spaces, lined by endothelium; thrombi, calcifications. Sometimes areas corresponding to capillary hemangioma are found as well.

Mixture of blood vessels separated by connective tissue and fat. The size of blood vessel lumens varies. Some may have thick wall composed of connective tissue and smooth muscle (van Gieson, smooth muscle actin), corresponding to arteries and veins. Staining for elastic tissue will show lamina elastica interna in arteioles; both arteries and veins usually have variable amount of elastic fibres within outer layers of their walls. Capillaries are often crowded and resemble capillary hemangioma closely. These areas may show proliferation with mitotic activity and sometimes resemble Kaposi's sarcoma (pseudo-Kaposi's sarcoma, but this term is used for irregular vascular proliferation caused by stasis in lower extremities as well); hemosiderin deposits may be present as well.

Variable, often large, thick walled venous blood spaces, thrombi, calcifications, variable dilatation of the venous spaces. Connective tissue, fat, muscle usualy separates the blood vessels. Large vascular spaces often dissect the connective tissue and its structures.

Inconspicuous areas with increased and dilated thin wall blood vessels. The histology is usually not diagnostic and clinicall correlation is required.

Dilated superficial capillaries, vascular anomaly.

Irregulary dilated capillaries within areas of solar elastosis. Sometimes bleeding is present.

Superficial vascular dilatations, newly formed blood vessels, sometimes with thickened walls.

Cavernous vessels with thin walls, containing thrombi. Between these spaces there are areas of spindle cells and fibrocytes (vimentin positive). The spindle cells are positive for ASMA (marker for pericytes) and mostly negative for endothelial markers (CD31, CD34). Spindle cell areas contain polygonal, epithelioid endothelial cells (CD31 and CD34 positive) with vacuolated cytoplasm. The vacuoles are sometimes large, so that these cells may resemble fat.

Epidermal hyperplasia with hyperkeratosis in close apposition to capillary spaces (which are dilated, with thin wall).

Loose granulation tissue, many capillaries, mixed inflammatory infiltration with variable number of neutrophils

Remnants of a thrombosed blood vessel; organizing thrombus, granulation tissue, irregular vascular lumina and multiple papillary endothelial proliferations; endothelial cells are regular.

Capillary tumorous proliferation, lobulary arranged. Sometimes with residual inflammatory infiltrate.

Corresponds to capillary hemangioma.

Roundish nodules of capillaries, partially solid, forming so called cannonballs within the dermis. On the periphery there are slit-like blood vessels and. CD31 and ASMA (marker for pericytes) are positive. No inflammatory infiltrate, no cellular atypia, thromboses nor deposits of hemosiderin. The infiltration is limited to the dermis.

Tumor consists of multiple small blood vessels of venular type in hyalinized or sclerotic stroma. The shape of the vessels is irregular, sometimes collapsed, antlers-like. Conspicuous layer of pericytes around these lumens is present (ASMA and smooth muscle actin positive), which is helpful in differential diagnosis against angiosarcoma or Kaposi's sarcoma. No cellular atypias and no inflammatory cells are present.

Histology corresponds to capillary hemangioma (but with hyperkeratosis, acanthosis and papillomatosis), but the tumor has deep part as well (the reason for recurences).

Superficially dilated blood vessels with prominent hobnail endothelial cells with intraluminal endothelial tufts (papillary endothelial protrusions). On the deep periphery slitlike vascular lumens. Slight lymphocytic infiltrate, sometimes single thrombi, usually prominent deposits of hemosiderin

Tiny hemangioma with central capillary, branching subepidermally.

Glomeruloid lesion consisting of blood vessels of varying size, thick walled; the lesion is small, roundish, well circumscribed.

Hemangioma, consisting of dilatated blood vessels with thin, regular endothelium and well defined vascular lumens. Stroma is often fibrotic.

Increased number of capillaries with activated endothelium, forming convolutes. Dense lymphocytic infiltrate with (usually many) admixtured eosinophils. Vacuoles within the endothelial cells. The infiltrate often forms reactive centers.

Lymphocytic infiltrate with admixtured eosinophils, dilatated blood vessels.

Vascular proliferation with large, activated epithelioid endothelia, high mitotic activity; inflammation with neutrophils (with leukocytoclasia), accumulations of finely granular material (bacteria) which are visible in HE and can be stained by silver impregnations (Warthin-Starry).

Proliferation of capillaries, bleeding, siderophages, chronic inflammation.

Tumor with unsharp borders, sometimes of angiocentric growth or association with large blood vessel. Skin infiltration is usually secondary. The cells are epithelioid, with pink, broad cytoplasm, often with vacuoles. High mitotic activity (over 2/10 HPF) and cytologic atypia are signs of more aggressive behaviour. Roundish or (short) spindle cells form nest and short fascicles, with infiltrative growth. Stroma is usually hyalinized or of chondroid appearance. Vascular markers (CD31, CD34, f. VIII.) are positive.

Vascular tumor with unsharp borders, located within reticular dermis and subcutaneous fat, composed of vertically oriented, braching blood vessels. Deposits of hemosiderin. The tumor usually does not destroy underlying tissue. Cellular atypias are nor prominent. Lymphocytic (B and T lymphocytes) are present within the tumor. Intravascular papillary projections are present. Vascular markers (CD31, CD34, f. VIII.) are positive.

Large tumorous masses, infiltrative, consisting of spindle cells with focal formation of slit-like lumina. Deep extension, infiltration of deep soft tissues and bone. CD31 and CD34 positive, f. VIII. positivity is variable. Areas of fibrosis or vascular differentiation may be present.

Irregular blood vessels, atypical endothelial cells (reacting rather like lymphatic vessels).

3 stages of development:

Macular stage: increased cellularity within the dermis; irregular spaces between colagen fibres lined by endothelium, focally containing erythrocytes. The blood vessels, which were formerly present, remain preserved and bulge into newly formed vascular spaces.

Stage with plaques: irregular vascular dermal spaces are clearly recognisable. Endothelial cells are irregular, with some mitotic activity. Aggregates of fusiform cells with hyaline inclusions and fagocytized erythrocytes are present, as well as coins-like arrangement of erythrocytes. No thromboses can be found. Focally there are deposits of hemosiderin and hemorrhage; plasmocytes are admixtured to the infiltrate.

Tumorous stage: nodules of fusiform cells, mitotic activity, hyalin globules, erythrophagocytosis.

Irregular and slit-like vascular spaces within the dermis; atypical vessels around collagen fibres, dissecting through the dermal collagen; atypical endothelial cells; bleeding.

Fusiform, fine, often wavy cells and fine collagenous fibres; sometimes compact, sometimes loose or even myxoid. S100 protein is positive. Sometimes fine, scattered nerve fibres are present. No capsule is present.

Histological picture in type I. neurofibromatosis corresponds to multiple neurofibromas. With time malignant transformation is common.

Well demarcated proliferation of Schwann cells with elongated nuclei with roundish ends; chromatin is fine. The cells form loose fascicles with nuclei aligned in parallel arrays (Verocay bodies): structure Antoni A. Other areas of the tumor are less cellular, myxoid, edematous; aligning of nuclei is usually not conspicuous: Antoni B areas.

S100 protein is positive.

Irregular bundles of peripheral nerves, fibrous tissue.

Lobules of cells in myxoid matrix; S100 protein, vimentin and collagen IV. positive.

Cellular neurothekeoma is characterized as an dermal neoplasm composed of nests and fascicles of spindle-shaped and epithelioid cells, S100 negative and NKIC3 positive.

The tumor consists of roundish cells with broad, granular cytoplasm and small, regular, centrally located nuclei. S100 protein, NSE and PGP 9.5 are usually positive.

Pseudoepitheliomatous hyperplasia of overlying skin or mucosa is common.

Dense, often nodular infiltrate with reaction centers, reaching deep into the dermis or subcutaneous fat. The infiltrate is top heavy. No epidermotropism (grenz zone). Lymphocytes are regular.

Adnexal structures are not destroyed. Admixture of reactive inflammatory cells within the infiltrate (eosinophils, plasma cells). Dendritic cells and tingible body macrophages are present as well.

Immunophenotype and genetic features:

• T cells (CD3+, CD43+) surround B cells (CD20+).
• regular network of dendritic cells (CD21+) within the follicular structures.
• polytypic expression of kappa and lambda Ig light chains