Tumors of fibrous tissue are common and histologically diverse. In addition, new entities continue to be described. The behavior and overall prognosis of these lesions is highly varied, so precise classification is required. It cannot be emphasized enough that the behavior of fibrous tumors may be difficult to predict based on traditional histologic concepts. For example, the morphologic features of some tumors, such as low-grade fibromyxoid sarcoma (LGFMS) and atypical fibroxanthoma (AFX), do not reflect their biologic behavior. For this reason, the pathologist should not attempt to predict the clinical behavior of mesenchymal tumors without a firm histologic diagnosis.
BENIGN FIBROUS PROLIFERATIONS AND TUMORS
Hypertrophic scar and keloid
Wound healing may be associated with an abnormal connective tissue response and result in exuberant scar formation. Hypertrophic scars and keloids occur most commonly in children and young adults (Table 30-1). They show a strong predilection for darkly pigmented individuals, particularly African Americans. Keloids occur most commonly in the head and neck, upper chest, and shoulder region. Most hypertrophic scars and keloids develop soon after surgical or other traumatic injury. Keloids are raised, shiny, smooth, and well-circumscribed plaques. They tend to extend beyond the original site of injury and may attain very large size through progressive growth. Hypertrophic scars, in contrast to keloids, do not usually extend beyond the site of original injury and tend to regress with time.
TABLE 30-1Hypertrophic Scar and Keloid |Favorite Table|Download (.pdf) TABLE 30-1 Hypertrophic Scar and Keloid
|Clinical Features |
|Most common in children and young adults |
|Predilection for African Americans |
|Head and neck, upper chest, and shoulder region |
|Raised, shiny, smooth, and well-circumscribed plaques |
|Extend beyond the original site of injury |
|Tend to grow progressively |
|Hypertrophic scar |
|Do not extend beyond the original site of injury and tend to regress |
|Histopathologic Features |
|Early scars: fairly cellular, fibroblasts arranged in parallel array |
|Sparse chronic inflammatory cells may be present |
|Cellularity decreases and collagenization increases with age |
|Long, slender blood vessels oriented perpendicularly to the epidermis |
|Keloids have thick bands of “glassy” hyalinized collagen |
|Differential Diagnosis |
Early scars may be fairly cellular and are composed of plump myofibroblasts and fibroblasts arranged in parallel array (see Table 30-1). Sparse chronic inflammatory cells may be present, particularly in early scars. As the scar ages, cellularity decreases, and collagenization increases. A characteristic feature of hypertrophic scars, which often tend to be nodular, is the presence of long, slender blood vessels oriented perpendicular to the epidermis. Keloids are similar histologically to hypertrophic scars but with the addition of characteristic thick bands of “glassy” hyalinized collagen (Fig. 30-1).
Keloid. (A) Scanning magnification image of a typical keloid. (B) Thick bands of “glassy” hyalinized collagen are ...