Dermal Lesions

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Dermal lesions due to abnormal blood vessels are common, most being developmental malformations rather than true neoplasms}

The most frequently seen vascular lesions in the dermis are hamartomatous, and the most common examples include capillary haemangioma, cavernous haemangioma and port-wine stain.

Capillary haemangiomas are common in babies (strawberry naevus) and are usually located on the trunk, buttocks or face. They are not present at birth, but manifest in the first few months of life; they spontaneously enlarge and then regress over the first couple of years of life. These firm, dark pink tumours protrude from the surface of the skin and are usually 2-3 cm in diameter.

Cavernous haemangiomas are clinically similar to capillary haemangiomas, occurring in the same location and in the same group. However, they tend to be larger, less clearly defined, and show no tendency to involution.
Port-wine stain usually presents at birth as a flat, purplish red or pink area on the face and neck. It occasionally arises on the limbs. These lesions show no tendency to regress and may continue to grow; they are sometimes associated with intracerebral vascular malformations (Sturge-Weber syndrome).

Pyogenic granuloma is a common, raised, red, vascular-looking lesion. Histologically it appears to be composed of highly vascular granulation tissue with inflammatory cells in the stroma. Often showing surface ulceration, they grow rapidly up to 1-2 cm in a matter of weeks until they are pedunculated red nodules. They are most common on the head and neck, and also involve the buccal and gingival mucosa, particularly in young pregnant women. They also occur on the limbs, particularly around the lower arms and hands, and there is sometimes a history of penetrating trauma.

The most important true tumours of vascular origin in the skin are glomus tumour, angiosarcoma and Kaposi's sarcoma

Glomus tumours most commonly occur in the fingers, particularly underneath the fingernails. They are small, reddish nodules (sometimes slightly blue), which are exquisitely tender particularly when pressed, but may also be spontaneously painful. They are derived from special arteriovenous anastomoses called 'glomus bodies', which are most frequently found in the hands.

Angiosarcoma is a highly malignant tumour in the skin. It is usually seen in elderly people, arising mainly in the head and neck region, particularly the scalp and forehead. Lesions appear as slightly raised purplish red patches or plaques, which spread and then undergo ulceration.

Kaposi's sarcoma was formerly uncommon in the Western World, being mainly confined to Central Africa. However, occasional cases were seen in elderly Caucasians, usually men, and principally in the hands and feet.

Kaposi's sarcoma has become a much more important tumour because of its high incidence in young adults (mainly males) who have AIDS; in this group the lesions are often multiple and grow rapidly, sometimes involving the oral mucosa, with a tendency to metastasize widely. They usually begin as a small, reddish patch, which enlarges and becomes a raised plaque or nodule. 
Histologically the tumour has a pattern of vascular channels surrounded by spindle-cell stroma with variable pleomorphism. The cell of origin of this tumour is in dispute, but it is probably derived from the endothelial cells of blood or lymphatic vessels.

Fibrous histiocytic tumours are the most common true tumours of the dermis

The cell of origin is considered to be the myofibroblast, a connective tissue cell that shows features of smooth muscle and fibroblast, together with some histiocytic characteristics. 

Fibrous histiocytic tumours arise most commonly on the limbs in middle-aged adults, and are slightly more common in women. The lesions are solitary raised nodules, usually brownish in colour, and the overlying epidermis may show some thickening and hyperkeratosis. 

The most common histological pattern is that of dermatofibroma in which the dermal nodule is ill defined and composed of spindle-shaped myofibroblasts which lies between dermal collagen bands, expanding the dermis. Of the two less common variants, one (histiocytoma cutis) contains a much higher proportion of lipid-filled histiocytic cells, giving the lesion a yellow colour on cut surface; this is particularly common around the ankle. The other variant, the so-called 'sclerosing haemangioma' is more densely sclerotic, with increased numbers of vessels. Often haemosiderin from leaked blood gives the lesion a brownish cut-surface appearance.

Dermal fibrous histiocytic tumours of this type are entirely benign, but there are two tumours with histological similarities, which behave as malignant tumours. Dermatofibrosarcoma protuberans is a much larger, slowly growing dermal tumour, which is irregular in outline and has multiple nodules within it. Malignant fibrous histiocytoma is one of the most common soft tissue tumours affecting the deep tissues (particularly of the thigh and buttock), but some malignant fibrous histiocytomas appear to arise in subcutaneous fat and may initially present as a deep skin tumour.

Non-neoplastic fibrous lesions of the dermis are common

The most common non-neoplastic fibrous lesions of the dermis are keloids. These occur as raised, firm, collagenous lesions, which are often covered by smooth, rather thin epidermis. They grow slowly and become harder with time.
They are usually found around the head, neck, upper chest and upper arms of young people (there is a female preponderance), and young women of Afro-Caribbean origin are particularly prone. Lesions follow a history of trauma, e.g. keloids on the earlobe are commonly the result of ear piercing, and keloidal change in surgical scars is an important cosmetic problem in the areas of the body where keloid change tends to occur. 
They probably represent excessive reactive collagen formation by fibroblasts after trauma, with the proliferation of fibroblasts and collagen deposition extending beyond the original site of trauma. In this way they are distinguished from hypertrophic scarring, in which a slowly resolving scar remains localized to the area of trauma.

Neurofibromas may be solitary or multiple; neurilemmoma is a solitary tumour

Neurofibromas are characteristically soft, raised, fleshy dermal tumours, which are often pedunculated.

In von Recklinghausen's disease there are large numbers of such tumours in many areas of the skin, and similar lesions are present in the internal organs. They are complex benign tumours containing Schwann cells, but elements of endoneurium and perineurium are also present; they are sometimes considered to be hamartomatous malformations. Malignant change may occasionally supervene in one of the larger skin tumours in von Recklinghausen's disease, but the solitary tumours are benign.

Neurilemmomas are solitary tumours of the Schwann cells of peripheral nerves, and usually lie in the line of a peripheral nerve. They are usually located in the sub-cutis rather than the dermis. They occur in middle-aged adults, with equal sex incidence, and are mainly seen on the limbs and head and neck. They are benign, but may undergo degenerative change if long-standing (ancient Schwannoma).
Leiomyomas in the skin are derived either from the walls of dermal vessels or from arrector pili muscles. They present as raised, red lesions, up to 1 cm across, and are both painful and tender. Those derived from arrector pili may be multiple and usually arise on the trunk and limbs in young adults; those derived from blood vessel smooth muscle are usually solitary, and may be larger than 1 cm in diameter.

The most common lymphoma to present in the skin is cutaneous T-cell lymphoma (CTCL)

B-cell lymphoma in the skin usually occurs as part of a systemic lymphoma. It manifests either as a solitary, raised, reddish purple nodule or as a series of coalescing nodules, particularly in the head and neck. 
T-cell lymphoma may present in the skin, sometimes remaining in the skin for many years before becoming systematized. The florid lesions of T-cell lymphoma in the skin are known as 'mycosis fungoides', appearing as multiple, raised, red nodules or indurated plaques. However, many patients have a long history of red skin patches with a wrinkled, scaly surface (often for many years), which occasionally become slowly more raised to form reddish confluent plaques. Histologically these are manifestations of infiltration of upper dermis and epidermis by increasing numbers of malignant T-lymphocytes and are known respectively as the 'patch' and 'plaque' stages of CTCL. 
By the time the patient has developed a nodular lesion of mycosis fungoides, the dermis contains nodular infiltrates of malignant T-lymphocytes.

Some patients with CTCL present with general widespread reddening of the skin (erythroderma), and a few of them have lymphadenopathy and malignant T-lymphocytes in the peripheral blood (S؛zary's syndrome).
There are many conditions that mimic CTCL both clinically and histologically, and the diagnosis of the disease may be difficult until the late stages, when plaques and nodular tumours are prominent.
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