Benign tumors and reactive proliferations
Osteoma Cutis
Definition
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Osteoma cutis represents a reactive, metaplastic, lamellar bone formation in the dermis and/or subcutis
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Primary and secondary forms of osteoma cutis can be separated on the basis of the absence or presence of an underlying skin disorder
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Primary osteoma cutis develops in normal skin or in the absence of an identifiable skin disorder (idiopathic)
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Secondary osteoma cutis always arises in previously damaged skin (e.g., in abnormal skin)
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Primary osteoma cutis can be isolated (e.g., nonsyndromic) or associated with various syndromes, including myositis ossificans progressiva, progressive osseous heteroplasia, fibrodysplasia ossificans progressiva, Albright hereditary osteodystrophy, and platelike osteoma cutis, or metabolic disorders like pseudohypoparathyroidism and pseudopseudohypoparathyroidism
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Secondary osteoma cutis develops in the background of a preexisting inflammatory skin condition (acne, folliculitis, localized scleroderma, dermatomyositis, scars, infections, chronic venous insufficiency, among others), neoplasia (pilomatricoma, chondroid syringoma, melanocytic nevus, basal cell carcinoma, among others), or other conditions (trauma, Becker nevus, among others)
Clinical features
Epidemiology
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Primary osteoma cutis represents about 15% to 30% and secondary forms represent about 70% to 85% of cases
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Plaquelike osteoma cutis
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Congenital or within the first year of life
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Acquired lesions presenting in adults appear to be more common in males, with predilection for the head, and especially the face
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Multiple miliary osteomas
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Middle-aged Caucasian women
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History of severe acne in about 55%, also reported after bisphosphonate (alendronate) therapy for osteoporosis, artificial tanning, severe blistering secondary to sunburn, and exogenous ochronosis
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Other types of secondary osteoma cutis
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No sex, age, or site predilection
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Presentation
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Asymptomatic, skin-colored papule(s), plaque(s), or nodule(s) of hard consistency
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Primary osteoma cutis
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Solitary, plaquelike, multiple, or widespread (disseminated)
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Can be the presenting sign of an underlying syndrome, especially in infancy
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Plaquelike osteoma cutis
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Reddish or skin-colored plaque of hard consistency
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Size usually less than 15 cm
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Predilection for scalp, face, and limbs, but any site can be affected
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Criteria for the diagnosis include
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Presence at birth or during first year of life
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At least one bony plate with/without other cutaneous osteomas
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No evidence of abnormalities in calcium or phosphorous metabolism
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No history of infection or trauma or any other predisposing event(s)
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Secondary osteoma cutis
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Solitary or multiple
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Multiple miliary osteomas
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Numerous skin papules
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Progressive increase in numbers and peripheral spread frequently reported
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Bluish hue of the papules, especially when history of minocycline treatment
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Size from 1 to 3 mm
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Scalp and face, followed by trunk, breast, extremities, and buttocks
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Prognosis and treatment
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Multiple lesions and plaquelike growth can be cosmetically disturbing
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Topical tretinoin therapy, surgical excision, needle mini-incision followed by osteoma extraction, laser treatment, dermabrasion
Pathology
Histology
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Lamellar mineralized bone, typically arranged concentrically in the dermis, subcutis, or both
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Osteocytes and osteoblasts embedded within the bone, most frequently at the periphery, whereas osteoclasts are much more infrequent
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Medullary spaces containing adipose tissue and variably abundant bone marrow (usually absent)
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Rim of fibroblasts frequently surrounds lamellar bone
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Transepidermal elimination of bony spicules occasionally present
Genetic profile
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GNAS gene mutations encoding G-protein alpha-stimulatory subunit in patients with progressive osseous heteroplasia, Albright hereditary osteodystrophy, platelike osteoma cutis, and pseudohypoparathyroidism type 1a
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ACVR1 gene mutations encoding receptors for bone morphogenetic proteins in patients with fibrodysplasia ossificans progressiva
Main differential diagnoses
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Osteochondroma (benign cartilaginous exostosis)
Tumoral Calcinosis
Definition
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The entity is characterized by calcium salt deposition in different periarticular soft tissues
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Although the term tumoral calcinosis has been used inconsistently in the literature for a variety of unrelated conditions having in common periarticular calcifications, including primary and secondary tumoral calcinosis, it should be restricted for hereditary conditions only (e.g., primary tumoral calcinosis)
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Two types of primary tumoral calcinosis have been recognized: (1) hyperphosphatemic type with familial basis caused by mutations in N-acetylgalactosaminyltransferase 3 ( GALNT3 ), KLOTHO or fibroblast growth factor 23 ( FGF23 ) genes and (2) normophosphatemic type with likely familial basis caused by mutation in the sterile alpha motif domain containing 9 (SAMD9) gene
Clinical features
Epidemiology
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Significant higher incidence in patients of African descent
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No sex predominance
Presentation
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Usually starts in the first and second decade of life
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Local, painless swelling progressing to firm mass with reduced joint mobility
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Ulceration of the overlying skin with secondary inflection not uncommon
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Pain inconsistent, usually associated with compression of the local nerve
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Predilection for large joints of the hips, shoulders, and elbows, less often hand and wrist
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Usually lobular/multilobular, densely calcified mass in the periarticular soft tissue, most commonly localized at the extensor surface of joints along the bursa
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Ocular involvement ranging from angioid streaks to corneal calcification deposits occasionally present
Prognosis and treatment
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Early surgical excision to prevent joint limitation(s), but associated with high recurrence rate
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Surgical excision combined with phosphate deprivation (aluminum hydroxide) in conjunction with acetazolamide has proven the most effective
Pathology
Histology
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Histological features depend on the stage of evolution
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Early lesions
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Multiple pseudocystic spaces filled with eosinophilic debris undergoing calcification
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Pseudocystic spaces lined by epithelioid macrophages and multinucleated giant cells
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Advanced lesions
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Densely calcified material
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Hyalinized connective tissue
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Immunohistochemistry/special stains
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Not contributory
Main differential diagnoses
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Calcinosis of chronic renal failure
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Calcinosis universalis (typically involving multiple tissue planes like subcutis, muscles, and fascia, frequently associated with connective tissue diseases)
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Calcinosis circumscripta (dermal and/or subcutaneous nodules at diverse sites, often in the context of connective tissue diseases)
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Calcific tendonitis
Soft Tissue Chondroma
Definition
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A benign, cartilage-forming tumor composed of lobules of mature hyaline cartilage occurring outside the skeletal system in the superficial or deep soft tissue(s)
Clinical features
Epidemiology
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Male predominance
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Most common in patients between 30 and 60 years of age
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Familial and congenital occurrence exceptional
Presentation
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Slowly growing, well-demarcated, asymptomatic mass or nodule
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Solitary lesions by far predominate
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Occasionally painful
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Lesions localized at the ungual/periungual site (e.g., nail matrix, nail bed) frequently associated with nail dystrophy/deformity
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Less than 2 cm in the majority of cases
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Closely associated with the tendon, tendon sheath, joint capsule, or periosteum
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Strong predilection for extremities (over 90%), in particular, hands and feet, with fingers being the most common single site
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Exceptional sites include dura, spinal canal, oral cavity, pharynx, larynx, skin, fallopian tube, and parotid gland
Prognosis and treatment
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Uniformly benign clinical course; no malignant transformation has been reported
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Complete excision curative
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Recurrences after marginal/incomplete excision in roughly 10% to 15%
Pathology
Histology
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Well-circumscribed, lobular/multilobular proliferation in the dermis and/or subcutis
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Mature adult-type hyaline cartilage is the principal, often exclusive, component of the lesion
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Mature chondrocytes, typically arranged in cords/rows
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Absent or mild nuclear pleomorphism
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Absent or a few normal mitoses
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Occasional binucleated cells (binucleated lacunae)
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Abundant chondroid matrix
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Chondroblastic variant
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Hypercellular proliferation in comparison with adult-type cartilage
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Immature cells, resembling chondroblasts
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Plump, rounded or spindled nuclei
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Prominent eosinophilic cytoplasm
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Considerable variation in size and shape (e.g., nuclear and cytological atypia)
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Normal mitoses can be present, but atypical mitoses absent
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The presence of immature cells is not related to biological potential
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Richly vascularized stroma
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Secondary changes (can be extensive)
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Calcifications, outlining lacunae in a “lacelike” or “chicken-wire” pattern, or more extensive (e.g., “tumoral calcinosis–like”)
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Metaplastic ossification, especially at the periphery of the lobules
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Myxoid change
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Cystic degeneration
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Hemorrhage
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Focal granuloma–like proliferation of histiocytes and osteoclast-like giant cells present in about 10% of the lesions, usually at the periphery of the tumor lobules
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Immunohistochemistry/special stains
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S100-protein positive
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Markers of epithelial differentiation negative
Genetic profile
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Cytogenetic analysis performed on limited numbers of soft tissue chondromas detected clonal chromosomal abnormalities in a subset of cases, none of them consistent, including monosomy of chromosome 6, rearrangements of chromosome 11, supernumerary rings derived from chromosome 12, and rearrangements of chromosome 12q13–q15
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Activating IDH1 mutations are not seen
Main differential diagnoses
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Enchondroma
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Synovial chondromatosis
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Skeletal chondrosarcoma extending into the surrounding soft tissue
Fibroosseous Pseudotumor of the Digits
Definition
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A rapidly growing, bone-forming, reactive lesion that occurs almost exclusively on the digits and is thought to be triggered by trauma
Clinical features
Epidemiology
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Rare
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Wide age range with predilection for young adults
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Males more commonly affected
Presentation
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Rapidly growing
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Small lesion
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Nonspecific painful swelling
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Fingers more commonly involved than toes
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Predilection for proximal phalanx
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Lesions not attached to bone
Prognosis and treatment
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Simple excision
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Local recurrences are exceptional
Pathology
Histology
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Ulceration common
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Fairly circumscribed
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Mainly subcutaneous
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Edematous and myxoid stroma rich in blood vessels, nodular fasciitis–like
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Extravasation of red blood cells
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Scattered lymphocytes
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Fibroblasts and myofibroblasts with ill-defined, pink cytoplasm and a small nucleolus
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Osteoclasts
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Bone distributed randomly
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Bone trabeculae surrounded by osteoblasts and containing prominent osteocytes
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Mitotic activity often brisk
Immunohistochemistry/special stains
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Stromal cells are positive for smooth muscle actin
Main differential diagnoses
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Ossifying myositis
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Extraskeletal osteosarcoma
Myxochondroid Metaplasia of the Plantar Foot
Definition
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A reactive and likely metaplastic process probably triggered by repeated trauma and with features that are somewhat similar to those seen in equine digital cushion and nuchal fibrocartilaginous pseudotumor
Clinical features
Epidemiology
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Very rare
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Similar sex incidence
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Wide age range, including children
Presentation
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Nonspecific subcutaneous, sometimes painful, small mass
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Plantar aspect of the feet, including toes
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No connection to bone
Prognosis and treatment
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Simple excision
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No recurrences reported
Pathology
Histology
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Focally circumscribed
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Variably cellular
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Bland, spindle-shaped cells, probably fibroblasts
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Fibromyxoid stroma with focal basophilic chondroid-like material
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Cystic degeneration common in addition to fat necrosis, hemosiderin deposition, and vascular proliferation
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True cartilaginous differentiation lacking lobularity rarely seen
Immunohistochemistry/special stains
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Cells within basophilic areas and those in areas with true cartilaginous differentiation are positive for S100 protein and ERG
Main differential diagnoses
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Nuchal fibrocartilaginous pseudotumor
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Soft tissue chondroma
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Fibroosseus pseudotumor of the digit
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