51

CASE 51


A 52-year-old white man presented to his family physician complaining of a bleeding growth on his nose. The patient states that his job requires him to frequently work outside and that he seldom uses protection against the sun even though he is of fair complexion. Visual examination of the growth showed that it was shiny and pink-colored with dilated blood vessels and a white rolled margin (Fig. 7-4A). The center of the papule was ulcerated and bleeding and measured 2 cm in diameter. Microscopic examination of a biopsy of the papule confirmed a diagnosis of basal cell carcinoma. The lesion was surgically excised.


image image

FIGURE 7-4 Basal cell carcinoma. A, Pearly nodule with blood vessels (telangiectatic). B, Nests of cells in the dermis.


(Kumar V, Abbas A and Fausto N: Robbins & Cotran Pathologic Basis of Disease, 7e. WB Saunders, 2004. Fig. 25-15.) C, Cleft separating cell nest from stroma. (Kumar V, Abbas A and Fausto N: Robbins & Cotran Pathologic Basis of Disease, 7e. WB Saunders, 2004. Fig. 25-15.)



HOW DOES SKIN FORM EMBRYOLOGICALLY?


The skin is formed from two germ layers. The epidermis is derived from ectoderm, whereas the underlying dermis develops from mesoderm-derived mesenchyme. The basic events of development of the epidermis are (Fig. 7-5):


• The primordium of the epidermis is represented by simple cuboidal ectoderm.

• At 4 weeks post-fertilization, a second epithelial layer has been formed by the mitotic activity of the basal layer. This superficial layer, the periderm, is composed of squamous cells that undergo keratinization and desquamation. Because of their mitotic capacity, the basal layer of cells is called the stratum germinativum.

• Continued mitotic activity of the stratum germinativum forms an intermediate layer of cells between it and the periderm. The intermediate layer forms at about 11 weeks.

• The stratum corneum replaces the cells of the periderm at approximately 21 weeks.

image

FIGURE 7-5 Stages of skin development. A, 4 weeks. B, 7 weeks. C, 11 weeks. D, Newborn.


(Moore K and Persaud TVN: The Developing Human, 7e. WB Saunders, 2003. Fig. 20-1.)


The dermis of the skin is primarily formed from the primitive mesenchyme. The mesenchyme that ultimately forms the dermis is derived from two mesodermal sources:


• Lateral somatic mesoderm

• Dermatomes of the somites

Most of the dermis differentiates from the lateral somatic mesoderm.



HOW IS SKIN ON THE NOSE DESCRIBED HISTOLOGICALLY?


Based on the thickness of the epidermis, skin can be classified as thin or thick. In this case, the skin on the nose is categorized as thin skin. Microscopically, four layers can be observed in the epidermis of thin skin. From deep to superficial, these layers are (Fig. 7-6):


• Stratum basale (also known as the stratum germinativum)

• Stratum spinosum

• Stratum granulosum

• Stratum corneum

image

FIGURE 7-6 Histologic features of thin skin. Note the presence of melanin in the basal layer of the epidermis.


(Kerr J: Atlas of Functional Histology. Mosby, 1999. Fig. 8-3b.)


Thick skin has the same four layers as thin skin, plus an additional layer called the stratum lucidum. The stratus lucidum is located between the stratum granulosum and the stratum corneum and its keratinocytes, which are devoid of organelles and contain keratin filaments and eleidin.


In the stratum basale, a single row of cuboidal to short columnar cells, termed keratinocytes, rests on a basal lamina. The mitotically active cells of the stratum basale are joined to one another and to the cells in the stratum spinosum by intercellular junctions.

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Jun 16, 2016 | Posted by in ANATOMY | Comments Off on 51

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