White : Diseases of the Skin - Benign Non-Melanocytic Tumors

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Gary M. White & Neil H. Cox

Diseases of the Skin

30	Benign Non-Melanocytic Tumors

DERMAL LESIONS

Fibrous lesions

Dermatofibroma (fibrous histiocytoma)

Etiology and pathogenesis

The dermatofibroma is an extremely common dermal fibrous tumor. It tends to occur on exposed sites on the limbs, and may represent some form of insect bite reaction. The upper back, especially over the scapula, is another typical area. It seems to be more common in women, but this may reflect a greater cosmetic awareness. Eruption of large numbers of dermatofibromas is uncommon but has been linked with HIV infection or its treatment.

Figure 30.27 Dermatofibroma, dimple sign. The center of a dermatofibroma will become depressed when lateral pressure is applied.

Figure 30.28 Dermatofibroma. The surface often takes on a brown, velvety appearance.

Figure 30.29 Multiple dermatofibromas (e.g. more than 10) may occur in patients with systemic lupus erythematosus.

Figure 30.30 Fibrous histiocytoma. The term fibrous histiocytoma is used by some to describe the larger, nodular lesions.

Clinical

Dermatofibromas have several morphologies (Figs 30.23 – 30.25). They may be pink, red (Fig.30.26), tan, or brown. The key distinguishing feature is that you can hold it between two fingers and feel it within the dermis (Fig.30.27). Often, when you do this, the surface will be ‘sucked in' (the dimple sign). The surface of the dermatofibroma is often pigmented, and at times, velvety (Figs 30.28 and 30.29). Lesions are usually solitary or few in number. Itch may occur (usually in early red-colored lesions) but will usually fade with time. The term fibrous histiocytoma is used by some to describe the larger, nodular lesions (Fig.30.30).

Differential diagnosis

Most lesions are readily diagnosed, but other chronic, solitary dermal papules or nodules may need to be considered.

•	Insect bite reactions—may actually be the cause of dermatofibroma.
•	Foreign body reactions—usually acral, unlike dermatofibroma.
•	Scabies nodules—often brown and itchy, more likely to be flexural or genital.
•	Melanocytic lesions: nevi, blue nevi, or melanoma—ordinary nevi are more rubbery and less tethered, and blue nevi are firm like dermatofibroma but usually a slate-blue color; darker dermatofibromas in particular may be referred as possible melanoma but are usually readily distinguished.
•	Angiomas—darker bluish-colored or deeply situated small angiomas may be in the differential.
•	Epidermal inclusion cyst—not usually difficult to distinguish, as they are smooth and mobile, with a central punctum, but previously ruptured cysts are more scarred and tethered.
•	Various appendageal tumors—Chapter 23.
•	Rarer lesions—for example metastases, calcification, and perforating disorders.

Figure 30.31 Acquired digital fibrokeratoma. Note the peripheral collar.

Figure 30.32 Acquired digital fibrokeratoma.

Figure 30.33 Acquired digital fibrokeratoma shaped like a conical tower.

Treatment

One can cut off the top, but often a scar forms about the same size. One can cut it out completely, but this will leave a substantial straight-line scar. Usually, no treatment is best. A strong topical or intralesional steroid may avoid surgery in symptomatic early lesions if there is no diagnostic doubt.

PRACTICE POINTS

•	Seborrheic keratoses are far, far commoner than melanoma; while it is important not to miss a melanoma, it is also important not to perform undue surgery for a common benign disorder.
•	Firmness and tethering are the classic features of a dermatofibroma but can’t be appreciated without palpation.
•	If a solitary ‘wart’ of the finger resists multiple freezings, perhaps it actually represents an acquired digital fibrokeratoma.
•	The term ‘skin tag’ in common usage does not necessarily imply a specific diagnosis; it may be used to describe the common fibroepithelial polyps, or it may be applied to nevi (usually small, pale, and ‘neurotized’) or to neurofibromas. If tags are solitary or few, and are not on the neck or flexures, the latter disorders are more likely than fibroepithelial polyps, and it is prudent to have histologic confirmation of the diagnosis.

Figure 30.34 Acquired digital fibrokeratoma will occasionally occur on the heel. Note the typical appearance of a flesh-colored nodule surrounded by a collarette.

Figure 30.35 Multiple skin tags of the axilla. Patients often want these tags removed because they irritate.

Acquired digital fibrokeratoma

Acquired digital fibrokeratoma represents a fibrous growth arising from the dermis. It occurs most commonly on the fingers. A flesh-colored papule on the finger, usually the index or middle finger, with an epidermal collarette at the base is characteristic (Figs 30.31 – 30.33). Occasionally, they may be warty or pedunculated. These lesions may also occur on the toes, palms, or the heel (Fig.30.34). Average age of onset is in middle age.

The main diagnosis to exclude is a wart. Warts classically possess black dots and tend to be multiple. Thus a solitary wart, which at the time you see the patient does not happen to have black dots, may pose a diagnostic dilemma. Freezing is appropriate. The worst that will happen is that the digital fibrokeratoma will not resolve. In younger patients, accessory digit is also a possible differential.

No treatment is needed; however, simple shave excision is effective.

Figure 30.36 Dermatosis papulosa nigra presenting as multiple tags of skin.

Figure 30.37 Necrotic skin tag. Skin tags may occasionally rotate on their base, cutting off their blood supply and causing inflammation and/or necrosis.

Figure 30.38 Skin tag. This larger lesion (cf. Fig. 30.36) is better snipped than frozen.

Figure 30.39 Epidermal inclusion cyst (EIC). Most EICs on the digits develop after trauma. No pore is usually seen.

Figure 30.40 Epidermal inclusion cyst (EIC). (a) This dermal nodule with a whitish hue and a central pore has the classic appearance of an EIC. (b) Multiple EICs often occur behind the ear.

Figure 30.41 Epidermal inclusion cyst (EIC). This lesion is dark because the internal keratin has oxidized.

Figure 30.42 Giant comedone. The pore of an epidermal inclusion cyst may be rather large, forming a giant comedone.

Skin tags (fibroepithelial polyps)

Skin tags are extremely common, flesh-colored, pedunculated tabs of skin that usually arise in flexural areas (the neck, axilla (Fig.30.35), groin, or under a woman's breasts). There is some correlation with weight, but many thin people get them as well. Seborrheic keratoses and dermatosis papulosa nigra often appear as tags of skin (Fig.30.36). It should be noted that some use the term skin tag morphologically to refer to a pedunculated, flesh-colored lesion. Histologic examination, especially when the tag is solitary, may reveal a nevus or neurofibroma. Others use the term skin tag to refer to lesions that histologically are fibroepithelial polyps. These lesions tend to be multiple and flexural. The important issue is that ‘skin tag' in common usage does not necessarily imply a specific diagnosis. Occasionally, tags will twist on their base and become necrotic (Fig. 30.37).

No treatment is needed, but small tags may be frozen (but not in a darker-skinned patient, as a white spot may result) or simply snipped off with scissors (Fig.30.38) without any need for anesthesia. The latter is recommended in darker-skinned patients. The patient with tags treated by freezing should be told that they will turn into a scab and fall off in about a week. Larger tags (e.g. greater than 3mm) are probably best snipped but may require lidocaine anesthesia at the base, and possibly electrocautery for hemostasis.

Cysts

Epidermal inclusion (epidermoid) cyst

Etiology and pathogenesis

The epidermal inclusion cyst (EIC), or epidermoid cyst, represents a sphere of epidermis oriented inward, buried within the skin. The epidermal wall constantly sheds keratinocytes into the lumen, causing the cyst to enlarge over time. These lesions may occur after trauma (Fig.30.39) or begin as a bulge off a hair follicle. The term sebaceous cyst is incorrect.

Clinical

A smooth spherical dermal nodule, at times with a visible pore (Figs 30.40 – 30.42), is a common presentation of an EIC. The back, and the head and neck, are common sites. When superficial, the nodule may be whitish. The lesion grows slowly over time and may periodically drain. The patient may complain that the extruded material smells foul. The cyst wall may rupture into the dermis, causing an intense inflammatory foreign body response. Swelling, erythema, and pain develop first. Later, the nodule may become fluctuant and drain spontaneously. Culture may show staphylococci, streptococci, or anaerobes, although a recent study showed no difference in the milieu between an intact and a ruptured EIC (Figs 30.43 and 30.44). Such rupture alters the clinical features, as the cyst loses its smooth contour and becomes tethered.

Figure 30.43 Ruptured epidermal inclusion cyst.

Figure 30.44 Ruptured epidermal inclusion cyst.

Differential diagnosis

An EIC that has not ruptured may be confused with the following.

•	Pilar cyst—on scalp, no central pore
•	Dermoid cyst—usually temple or above eyebrow in a child.
•	True sebaceous cyst—rare, occurs as multiple lesions in a disorder termed steatocystoma multiplex.
•	Lipoma—usually obviously softer, less well defined, no punctum, but may be difficult to distinguish at sites where the skin is thick.

An EIC that has previously ruptured may be confused with a much wider spectrum of options, including many discussed earlier in the differential of dermatofibroma, the most important, although rare, being metastatic disease or primary skin malignancy (especially sarcomas).

Treatment

The non-inflamed EIC may be left untreated. However, if it is bothersome to the patient, it may be surgically excised. Removing the cyst intact gives the surgeon confidence that the lesion will not recur. Simple drainage or any other technique that leaves any portion of the cyst wall may lead to recurrence. The inflamed EIC should be treated with warm compresses, and incision and drainage, if fluctuant.

Figure 30.45 Milia. Tiny, white spheres are common about the eyes of women. Patients often think these are clogged pores, but they never seem to resolve.

Figure 30.46 Milia en plaque. This lesion on the forehead was excised due to concern about basal cell carcinoma, but histology showed it to be a dense group of milia. At more typical sites on or behind the ear, some of these cases respond to minocycline.

In some patients, provided that there is no active infection, intralesional steroid injection may shrink the cyst or prevent recurrent inflammatory episodes. It should also be considered for previously ruptured cysts, as operating on such lesions is often difficult due to vascularity and scar tissue that make it difficult to delineate the cyst wall.

PRACTICE POINTS

•	Simply draining an epidermal inclusion cyst is not adequate therapy. The remaining cyst wall will merely produce more keratin, refilling the cavity. Complete surgical removal of the intact cyst is preferred.
•	Intralesional steroid injection is a useful option for previously ruptured cysts, as operating on such lesions is often difficult due to vascularity and scar tissue that make it difficult to delineate the cyst wall.
•	Beware of delegating excision of pilar cysts of the scalp or of previously ruptured cysts to the junior member of the team; these operations seem simple, but a large dead space and tight skin on the scalp or back may cause significant problems with hemostasis.

Milia

The milium represents a miniature EIC. It occurs most commonly on the face of an adult woman but may occur in the healing phase of certain diseases (e.g. porphyria cutanea tarda) or on the faces of neonates. Multiple milia of the face occur in the rare Bazex syndrome. A potent topical steroid may induce these lesions. Asymptomatic, 1–3-mm, white papules about the eyes and face are characteristic of milia (Fig.30.45). Most patients want their milia removed for cosmetic reasons. A 20-gauge needle may be used to extract milia without anesthesia. There is no real differential diagnostic issue for typical tiny lesions, but larger firm white lesions might represent calcinosis, gout, or pus.

Figure 30.47 Pilar cysts or ‘wens’ occur almost exclusively in the scalp. They ‘pop out’ easily during surgery, in contrast to epidermal inclusion cysts.

Figure 30.48 Pseudocyst of the auricle is a degenerative condition of the cartilage, which causes an apparent deep, smooth, cystic nodule.

Milia en plaque

Rarely, milia may occur in an aggregated form. This entity has been described under several names and variants, including follicular lichen tumidus and lichen planus follicularis tumidus with cysts and comedones. Multiple, aggregated, white papules occurring behind the ear or preauricularly are most characteristic, but any site may be affected (Fig.30.46). Treatment is not necessary, but tretinoin may work and some respond to minocycline. Individual milia may be extracted; large lesions can be excised.

Pilar cyst

The pilar cyst is akin to the EIC, but the wall histologically resembles the external hair root sheath. Solitary or multiple, round, dermal nodules of the scalp are characteristic (Fig.30.47). They may occasionally occur elsewhere on the body. Inheritance is autosomal dominant. Surgical excision may be performed. These cysts often ‘pop out' easily, in contrast to EICs.

Figure 30.49 Ganglion cyst.

Figure 30.50 Neurofibroma. A solitary, flesh-colored papulonodule is characteristic. Often, the lesion can easily be pushed into the skin.

Pseudocyst

The pseudocyst is an intracartilaginous cystic lesion of the ear. It is not a true cyst, as it does not have an epithelial lining. A non-tender, firm, cystic lesion of the ear (Fig.30.48) is characteristic. It may be preceded by trauma, as occurred in two boys after ear pulling for their birthday. It may also be associated with atopic dermatitis. Drainage yields a thick, viscous fluid. All ages, including infants, may be affected.

Several successful approaches to therapy have been reported. After drainage, a sclerosing agent (e.g. 1% iodine or trichloroacetic acid) may be instilled and bolstering sutures placed. Alternatively, the anterior cartilaginous wall may be removed. Simple aspiration usually leads to recurrence.

Ganglion cyst

The ganglion cyst represents a cystic extension of the synovial lining of a subjacent joint. A 1–3-cm subcutaneous nodule overlying the ankle or wrist is typical (Fig.30.49). No treatment is needed. Surgical excision by an orthopedic surgeon is appropriate.

Lesions of nerve or muscle origin

Neurofibromas

The neurofibroma is a small dermal tumor of nerve tissue. As commonly occurs with adnexal tumors also, the sporadic type is solitary, whereas the inherited type is multiple (see neurofibromatosis, Ch.19). A soft, dermal, flesh-colored tumor is typical (Fig.30.50). Any area of the body may be affected. No treatment is needed, but a simple shave or elliptic excision may be carried out.

Figure 30.51 Solitary leiomyoma.

Figure 30.52 Multiple leiomyoma. Multiple, grouped, flesh-colored nodules are typical.

Figure 30.53 Large cutaneous solitary leiomyoma. This lesion had associated ossification, which is rare with leiomyoma.

Figure 30.54 Idiopathic scrotal calcinosis. Multiple white nodules on the scrotum.

Figure 30.55 Multiple miliary osteoma of the face.

Leiomyomas

Leiomyomas are red-brown, smooth, firm papules or nodules (Figs 30.51 – 30.53). They may be solitary, or may occur as multiple lesions grouped together; multiple lesions may number from several to hundreds and may be distributed linearly or within a dermatome. Leiomyomas may be quite painful. Familial cases have occurred, with the affected women having an increased risk of uterine leiomyoma. Nifedipine (10–30mg three times a day) has been given for the pain, as has phenoxybenzamine (an a -adrenoreceptor blocker; 10mg twice a day).

Calcinoses and bone formation

Idiopathic scrotal calcinosis

The current theory is that these calcified nodules of the scrotum arise through calcification of EICs. Multiple whitish papules or nodules, round like cysts, occur scattered over the scrotum (Fig. 30.54). No treatment is needed; however, excision of individual lesions may be performed.

Other calcium deposition disorders are discussed in Chapter 11.

Multiple miliary osteoma of the face

Multiple flesh-colored or whitish papules of the face are characteristic (Fig.30.55). Serum levels of calcium and phosphorus are normal. This entity has been reported in young women as a sequela of severe acne, or in older patients without a history of facial skin disease. Blue-brown discoloration of lesions has occurred in patients treated with tetracycline or minocycline. Rarely, patients may develop multiple papular lesions on the trunk.

Tretinoin has been used when the lesions are small and superficial. Surgical excision of each may be done. Alternatively, complete excision of the affected skin with flap repair, dermabrasion, and CO₂ laser excision has been reported.

Figure 30.56 Cutaneous focal mucinosis.

Figure 30.57 Cutaneous focal mucinosis. Deformation with a pen shows the characteristic ‘water bag’ sign.

Mucin deposition

Cutaneous focal mucinosis

A solitary, flesh-colored, or translucent papule that may, on palpation, resemble a tiny bag of water is characteristic (Figs 30.56 and 30.57). Simple excision or destruction is adequate.

A more comprehensive overview of mucinosis is given in Chapter 11.