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  • Benign tumours and cysts of the skin and its appendages

     

    THOMAS G. CROPLEY

     

     

    EPIDERMAL TUMOURS

    Seborrhoeic keratoses are common, benign lesions that appear in middle age (Fig. 1) 1503. They are most commonly located on the trunk, although the face, particularly the cheeks and temporal areas, is also frequently affected. Small seborrhoeic keratoses occur on the arms and legs, sparing the palms and soles. Lesions range in size from a few millimetres to several centimetres. Seborrhoeic keratoses are tan or light brown and commonly have a ‘stuck on’ appearance. Occasionally, lesions may be flesh coloured, pink, or even black: the resemblance of black seborrhoeic keratoses to malignant melanoma can be striking, and biopsy is indicated in this situation. The surface may be verrucous or smooth and waxy. Seborrhoeic keratoses have no premalignant potential. They can usually be distinguished from malignant melanoma, pigmented basal cell carcinoma, and naevi on clinical grounds; when there is doubt, an excisional biopsy should be performed. Removal of seborrhoeic keratoses is seldom indicated, except for cosmetic purposes. Removal may be accomplished by shave excision, curettage, or cryosurgery. Full-thickness excision and primary closure is not necessary: these lesions are proliferations of epidermal keratinocytes and do not extend into the dermis. The Leser-Trelat sign, in which the sudden eruption of innumerable seborrhoeic keratoses is reputedly associated with internal malignancy, is now thought to be a myth.

     

    Dermatosis papulosa nigra refers to the presence of numerous waxy black seborrhoeic keratosis-like papules that occur in the periorbital region. This entity is seen exclusively in black subjects, and is of cosmetic significance only. Although lesions may be treated by shave excision, electrofulguration, or cryosurgery, any treatment should be performed cautiously, since post-treatment pigmentary changes may be equally cosmetically distressing to the patient.

     

    Clear cell acanthoma is a common, benign tumour of the skin occurring primarily on the lower extremities. It appears as a shiny, red papule or plaque measuring up to 2 cm in diameter. The surface is frequently crusted. Histologically, the lesion consists of a proliferation of pale, glycogenated keratinocytes within the epidermis. The differential diagnosis of clear cell acanthoma includes squamous cell carcinoma, nodular malignant melanoma, and pyogenic granuloma. Excisional biopsy is usually indicated, and is curative.

     

    EPIDERMAL (SEBACEOUS) CYSTS

    Epidermal inclusion cysts, are often incorrectly referred to as sebaceous cysts and are the most commonly encountered cysts of the skin (Fig. 2) 1504. They may occur in childhood, but are more common in early adulthood; the most common sites are the scalp, face, and back. Lesions may be solitary or multiple, and present as 0.5 to 5.0 cm spherical, slightly compressible, intradermal or subcutaneous masses. A dilated follicular orifice may connect the cyst to the cutaneous surface, usually near the dome of the cyst. The wall of the cyst is composed of fully differentiated epithelium which reproduces the epidermis. Desquamated keratinocytes are shed into the centre of the cyst, forming a white cheesy material. Infection of epidermal inclusion cysts leads to fibrosis of the surrounding dermis. This event is of importance to the surgeon; previously infected cysts may be difficult to dissect and en-bloc excision is the treatment of choice. Cysts that have not previously been infected or manipulated surgically may be bluntly dissected free of the surrounding tissue following a simple equatorial incision of the overlying skin. Cysts on the face, however, should have their lining teased from within via a small incision to minimize cosmetic deformity.

     

    Multiple epidermal inclusion cysts may be associated with multiple colonic polyposis in patients with Gardener's syndrome. Milia are tiny epidermal cysts measuring no more than 1 or 2 mm which occur most frequently around the eyes. They may be removed with a needle or a No. 11 scalpel blade.

     

    Pilar cysts, also known as trichilemmal cysts, are less common than epidermal inclusion cysts, and occur almost exclusively on the scalp. They are indistinguishable from epidermal inclusion cysts on clinical grounds, although small pilar cysts on the scalp may feel quite firm, unlike epidermal inclusion cysts. The wall of a pilar cyst is composed of epithelium which resembles the outer root sheath of hair follicles. The cyst cavity is filled with dense glassy keratin, which resembles hair biochemically. Pilar cysts seldom become infected; they are usually easily removed by blunt dissection.

     

    Steatocystoma multiplex is inherited as an autosomal dominant trait. Multiple, thin-walled cysts develop during adolescence on the upper chest, neck, and back (Fig. 3) 1505. Aspiration of cyst contents may reveal a drop of oily fluid. Surgical treatment is usually not indicated; conservative management is frequently the best course.

     

    Digital mucinous cysts present as 4 to 5 mm diameter, bluish, cystic-appearing nodules overlying the distal phalanx proximal to the nail fold. A longitudinal groove may form in the adjacent nail plate as the result of downward pressure by the cyst on the nail matrix. Mucinous cysts are not true cysts, since they lack an epithelial lining. Rather, they consist of a focus of mucinous degeneration of the dermis. Treatment is difficult; excision usually requires an advancement procedure for closure, and may result in distortion of the nail. Cryosurgery frequently resolves the problem with less risk of nail distortion.

     

    DERMAL TUMOURS

    As a manifestation of neurofibromatosis, neurofibromas tend to be multiple, often occurring in hundreds. Most commonly, however, neurofibromas occur as solitary, harmless flesh-coloured tumours which protrude from the skin, without the associated findings of neurofibromatosis. Characteristically, neurofibromas invert partially when pressed with a finger (‘button-holing’). Patients who have a neurofibroma should be examined carefully for the presence of other, similar lesions, and for café-au-lait spots. Small solitary neurofibromas can be excised simply, but large lesions often have an extensive subcutaneous component. Careful preoperative palpation will allow their subcutaneous extent to be estimated.

     

    Dermatofibromas are common cutaneous lesions resulting from proliferation of dermal fibroblasts, usually on the lower extremities in women and on the trunk and upper extremities in men. Clinically, dermatofibromas are firm intradermal nodules, and feel as if a plastic button has been embedded in the skin. The overlying epidermal surface is frequently shiny or corrugated; hyperpigmentation is common. The differential diagnosis of dermatofibromas includes dermatofibrosarcoma protuberans, the malignant counterpart of dermatofibroma, metastatic carcinoma, Kaposi's sarcoma, and desmoplastic malignant melanoma. The correct diagnosis is usually apparent on clinical grounds, but incisional or excisional biopsy may be indicated in difficult cases. Treatment of dermatofibromas is often unsatisfactory; lesions frequently recur following excision because of inapparent involvement of the surrounding skin. The lesions also tend to occur in anatomical sites where excision scars may be a cosmetic problem. Unless dermatofibromas are particularly large or become irritated, it is often best to deal with them non-operatively.

     

    Acquired digital fibrokeratoma is a common lesion that develops on the lateral surface of a finger or toe in adults. Lesions are solitary, firm, and flesh-coloured; they may be dome-shaped or conical and are surrounded by a small collarette of skin (Fig. 4) 1506. Simple excision with primary closure is curative.

     

    Fibrous papule of the nose presents as a 2 to 3 mm diameter, superficial, dome-shaped, flesh-coloured papule on the nose or perinasal skin. Histologically, it consists of benign fibrovascular tissue. Lesions may resemble small basal cell carcinomas: the diagnosis of fibrous papule of the nose is frequently made postoperatively by the pathologist. No treatment is required.

     

    Leiomyomas of the skin are seen occasionally. They may be derived from vascular smooth muscle or from the erector pili muscles of the skin. Characteristically, leiomyomas are tender on palpation, and contract when exposed to cold. Lesions are frequently multiple, occurring in aggregates of 10 or more nodules within the skin. Excision is the preferred treatment, and is frequently indicated because of the discomfort associated with the lesions.

     

    Lipomas are familiar to most general and plastic surgeons. These benign tumours of the subcutaneous fat may become very large. Angiolipomas are highly vascular lipomas that frequently are tender. The frontalis-associated subfascial lipoma described recently by Salasche presents as a slightly protruding subcutaneous mass on the lateral forehead in older men. This type of lipoma is extremely difficult to dissect because of the highly vascular muscle which invests it. In general, however, lipomas are easily excised or removed by percutaneous liposuction.

    FURTHER READING

    Salasche SJ, McCollough ML, Angellon VL, Grabski WJ. Frontalis-associated lipoma of the forehead. J Am Acad Dermatol 1989; 20: 462–8.

    Saylan T, Marks R, Wilson Jones E. Fibrous papule of the nose. Br J Dermatol 1971; 85: 111–8.

    Verallo VVM. Acquired digital fibrokeratomas. Br J Dermatol 1968; 80: 730–6.



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