Cutaneous smooth muscle tumors





Benign tumors and hamartomas


Smooth Muscle Hamartoma


Definition





  • A hamartomatous lesion composed of a dermal proliferation of mature smooth muscle cells growing in haphazardly arranged bundles



Clinical features


Epidemiology





  • Slight male predominance



  • Prevalence of 1 in about 2700 live births



  • The majority of the lesions are congenital



  • Familial occurrence exceptional, with autosomal-dominant inheritance reported in some families



Presentation





  • Skin-colored indurated patch, plaque, follicular papules, or variably pigmented macules; occasionally associated with hypertrichosis



  • Usually asymptomatic, but can be pruritic



  • Stroking of the lesion can result in transient elevation of the affected area and piloerection due to smooth muscle contraction (pseudo-Darier sign)



  • Induration, hyperpigmentation, and hypertrichosis diminish over time



  • Unusual clinical presentations include linear, atrophic, or a morphea-like plaque



  • Multiple lesions or a generalized presentation very rare



  • The generalized variant occasionally part of the “Michelin-tire baby” syndrome, characterized by deep circumferential skin folds over the trunk and limbs with distinctive clinical appearance, mental retardation, and other developmental abnormalities



  • Predilection for lumbosacral area and proximal extremities



  • Uncommon sites include the head and neck, conjunctiva, nipple, and genital area



  • Rare associated conditions include Becker nevus, congenital melanocytic nevus, and basal cell carcinoma, with the latter two conditions likely to be coincidental



Prognosis and treatment





  • No treatment generally required



  • Surgical excision or laser treatment usually for cosmetic reasons



Pathology


Histology





  • Localized in the dermis, with occasional extension into the subcutis



  • Mature smooth muscle cells, growing in haphazardly arranged bundles



  • Mitotic activity absent



  • Association with morphologically normal hair follicles in about 40%



  • Prominent nerve fibers and collagen bundles usually present among smooth muscle bundles



  • Overlying epidermis normal or displays mild hyperkeratosis, acanthosis, and hyperpigmentation of basal keratinocytes



Immunohistochemistry/special stains





  • Smooth muscle actin, calponin, desmin, and h-Caldesmon positive



Main differential diagnoses





  • Becker nevus



  • Pilar leiomyoma (more orderly proliferation of smooth muscle bundles arranged in ramifying fascicles, intervening collagen more discrete)


Fig. 1


Smooth muscle hamartoma.

Low-power magnification showing multiple dermal bundles of smooth muscle cells identical to arrector pili muscles.



Fig. 2


Smooth muscle hamartoma.

Higher magnification depicting multiple arrector pili muscles.




Pilar Leiomyoma


Definition





  • A benign smooth muscle tumor composed of interlacing fascicles of bland spindle cells displaying typical features of smooth muscle differentiation (e.g., cigar-shaped or blunt-ended nuclei and bright eosinophilic cytoplasm)



  • Believed to arise from or differentiate toward the arrector pili muscle



  • Lesions can be solitary or multiple and develop either as a sporadic or inherited condition



Clinical features


Epidemiology





  • Most commonly develops in the second and third decades of life



  • Female predominance for multiple lesions, whereas solitary tumors occur more commonly in males



  • Congenital occurrence exceptional, likely overlapping with or representing a variant of congenital smooth muscle hamartoma



  • A subset of pilar leiomyoma(s) occurs in the familial setting, the so-called Reed syndrome or multiple leiomyomatosis




    • Autosomal-dominant mode of inheritance



    • Associated with germline mutation(s) of the fumarate hydratase ( FH ) gene on chromosome 1q42.3-43 acting as a tumor suppressor gene



    • Combination of multiple pilar and uterine leiomyomas, additionally complicated by development of a solitary multifocal or bilateral papillary renal cell carcinoma in roughly up to 20% of patients




Presentation





  • Firm and smooth, skin-colored, red-brown to violaceous papule(s) or nodule(s)



  • Multiple lesions




    • More common than solitary lesions



    • Size of individual lesion usually up to 1 cm in diameter



    • Often tender or painful, either spontaneously or in response to cold, pressure, or emotional stimuli



    • Show predilection for extensor surface(s) of the extremities and trunk



    • Distribution can be segmental, dermatomal, linear, zosteriform, or more widespread/diffuse




  • Solitary lesions




    • Most commonly develop on the limbs



    • Tend to be larger than multiple tumors



    • Frequently asymptomatic



    • Rarely presentation may be with an indurated plaque




Prognosis and treatment





  • Complete surgical excision curative, but difficult to achieve in multiple tumors



  • Recurrence rate as high as 50% for multiple lesions



Pathology


Histology





  • Dermal-based proliferation, extension into the subcutis infrequent



  • Poorly circumscribed and infiltrative, less often nodular and well circumscribed



  • Interweaving/interlacing fascicles of bland spindle cells displaying typical features of smooth muscle differentiation




    • Cigar-shaped or blunt-ended nuclei



    • Low mitotic activity present in roughly 30% of the lesions (fewer than 1 mitosis per 10 high-power fields)



    • Bright eosinophilic cytoplasm




  • Histological variants




    • Epithelioid



    • Symplastic




      • Pleomorphic cells with large, multilobated, hyperchromatic nuclei; macronucleoli; and intranuclear cytoplasmic pseudoinclusions, usually scattered among bland spindle cells



      • Multinucleated giant cells not uncommon



      • Mitotic activity low (usually fewer than 1 per 10 high-power fields)



      • Necrosis absent



      • Represents degenerative phenomenon





Immunohistochemistry/special stains





  • Positive for smooth muscle actin, desmin, calponin, and h-Caldesmon



  • A small percentage of cases express keratin



Main differential diagnoses





  • Cutaneous leiomyosarcoma



  • Metastatic leiomyosarcoma



  • Cellular dermatofibroma



  • Dermatofibrosarcoma protuberans with myoid nodules


Fig. 1


Pilar leiomyoma.

Low-power magnification showing poor circumscription of smooth muscle bundles.



Fig. 2


Pilar leiomyoma.

Poor circumscription is particularly evident at the periphery of the neoplasm.



Fig. 3


Pilar leiomyoma.

Low-power magnification demonstrating haphazardly arranged bundles of smooth muscle cells in the dermis.



Fig. 4


Pilar leiomyoma.

Note bundles of tumor cells with well-defined, pink cytoplasm and bland vesicular nuclei.



Fig. 5


Pilar leiomyoma.

Tumor cells with characteristic cigar-shaped vesicular nuclei and pink cytoplasm.




Genital Leiomyoma


Definition





  • A variant of leiomyoma arising from superficial smooth muscles at genital locations, including scrotum, vulva, and nipple



Clinical features


Epidemiology





  • Predilection for middle-aged adults



Presentation





  • Solitary, slowly growing papule or nodule, less often a pedunculated lesion with surface ulceration



  • Multiple lesions most uncommon



  • Lesions can increase in size during pregnancy



  • Most of the lesions are asymptomatic



  • Nipple leiomyomas




    • Tend to be smaller (generally less than 2 cm)



    • Poorly circumscribed




  • Vulvar and scrotal leiomyomas




    • Size generally between 3 and 5 cm in diameter



    • Well circumscribed




  • Vulvar leiomyoma(s) can be associated with synchronous or metachronous development of esophageal leiomyoma(s), a condition known as esophagovulvar syndrome



Prognosis and treatment





  • Complete surgical excision curative



Pathology


Histology





  • Histological features essentially similar to pilar leiomyomas, including the so-called symplastic change representing a degenerative phenomenon (see corresponding section on pilar leiomyoma)



  • Certain morphological features occur more commonly at genital sites (see below)



  • Vulvar and scrotal leiomyomas




    • More cellular than pilar leiomyomas



    • Tend to be better circumscribed and more nodular but not encapsulated



    • Focal or more widespread epithelioid morphology common



    • Myxoid change frequent, especially during pregnancy



    • Hyalinization of the stroma can be prominent



    • Variably intense perivascular inflammatory cell infiltrate composed of lymphocytes, histiocytes, and eosinophils




Immunohistochemistry/special stains/cytogenetics





  • Smooth muscle actin, calponin, desmin, and h-Caldesmon positive



  • Variable positivity (over 50%) for estrogen and progesterone receptors



  • Androgen receptor positivity in scrotal leiomyomas



  • No consistent cytogenetic change in vulvar leiomyomas, yet the data is limited



Main differential diagnoses





  • Angiomyofibroblastoma



  • Aggressive angiomyxoma


Fig. 1


Nipple leiomyoma.

Numerous variably sized bundles of smooth muscle cells are seen throughout the dermis.



Fig. 2


Nipple leiomyoma.

Bundles are composed of bland smooth muscle cells with round to cigar-shaped nuclei and pink cytoplasm.



Fig. 3


Nipple leiomyoma.

Perpendicular section through smooth muscle bundles reveals tumor cells with round to oval nuclei and abundant well-defined, pink cytoplasm. Note the absence of nuclear atypia and lack of mitotic activity.



Fig. 4


Nipple leiomyoma.

Parallel section through smooth muscle bundles with characteristic bland, cigar-shaped nuclei and brightly eosinophilic cytoplasm.




Angioleiomyoma


Definition





  • A benign tumor composed of vascular smooth muscle cells and blood vessels



  • Alternatively designated as a vascular leiomyoma or angiomyoma



  • This tumor is now regarded as part of the spectrum of pericytic (perivascular) tumors that include glomus tumor and its variants, and myopericytoma and its variants



Clinical features


Epidemiology





  • Slightly more common in females



  • Wide age distribution from 12 to 84 years, the majority present between the fourth and sixth decades of life



  • Congenital presentation exceptional



Presentation





  • A solitary, slowly growing, and firm subcutaneous nodule



  • Tenderness and pain, often paroxysmal, reported in up to 60% of the lesions, with the remaining lesions asymptomatic



  • Size usually less than 2 cm in about 80% of the lesions



  • Predilection for extremities, in particular, lower extremities (about 70%), followed by upper extremities and head and neck



  • Unusual locations include intracranial site (dura) and intraosseous occurrence



Prognosis and treatment





  • Complete or marginal surgical excision generally sufficient



  • Recurrences exceptional, usually related to incomplete excision



Pathology


Histology





  • Well-circumscribed proliferation in the subcutis, less often in the dermis



  • Two main components are (1) bland smooth muscle cells and (2) blood vessels



  • Smooth muscle cells




    • Grow in interlacing or disorganized bundles



    • Appear to originate from the vessel walls



    • Perivascular concentric arrangement overlapping with myopericytoma occasionally present



    • Pointed nuclei, tapering eosinophilic cytoplasm



    • No cytological atypia or, when present, focal and degenerative in nature (see later)



    • Mitoses generally absent or very limited in numbers




  • Three subtypes of angioleiomyoma can be separated on the basis of the morphology of the vascular channels




    • Solid type




      • Most common type



      • Closely packed bundles of spindled smooth muscle cells



      • Intervening vascular channels with small slitlike lumina and thin vessel walls




    • Venous type




      • Intervascular smooth muscle cells blend with smooth muscle cells of the vascular walls



      • Thick muscular vessel walls




    • Cavernous type




      • Least common type



      • Small amounts of intervascular smooth muscle cells



      • Intervascular smooth muscle cells difficult to separate from smooth muscles cells of the vascular walls



      • Dilated vascular channels





  • Histological variants




    • Epithelioid



    • Clear cell



    • Symplastic




      • Marked degenerative cellular atypia(s) and prominent nuclear pleomorphism



      • Absence of mitotic activity in pleomorphic cells





  • Additional histological features present in a small proportion of the cases




    • Intralesional fat



    • Inflammatory cell infiltrate, composed predominantly of lymphocytes with occasional formation of aggregates



    • Collagen hyalinization



    • Foci of calcification



    • Areas of hemorrhage and/or deposition of hemosiderin pigment



    • A feeding medium-sized artery




Immunohistochemistry/special stains





  • Smooth muscle actin, muscle specific actin, calponin, and h-Caldesmon positive



  • Variable desmin positivity



  • Negative for keratins, S100 protein, CD34, CD31, and HMB45



Genetic profile





  • No consistent genetic changes have been detected



  • Various gains and losses of chromosomes in about one-third of the cases



Main differential diagnoses





  • Leiomyoma



  • Myofibroma



  • Myopericytoma (morphological and immunohistochemical overlap with angioleiomyoma)


Fig. 1


Angioleiomyoma.

Low-power magnification reveals a well-circumscribed proliferation of smooth muscle cells growing in haphazardly arranged fascicles in the dermis and subcutis.



Fig. 2


Angioleiomyoma.

In addition to smooth muscle cell proliferation, numerous small blood vessels are present within the lesion with encircling smooth muscle and represent an integral part of the tumor.



Fig. 3


Angioleiomyoma.

Smooth muscle cell and vascular proliferation—higher magnification.




Cutaneous Leiomyosarcoma (Atypical Intradermal Smooth Muscle Neoplasm)


Definition





  • A distinctive smooth muscle tumor localized in the dermis or associated with limited extension into the superficial subcutis (generally less than 5 mm), characterized histologically by mitotic activity, cellular pleomorphism, and, much less often, tumoral necrosis



  • Although such lesions have been classified as cutaneous leiomyosarcoma, they invariably follow a benign clinical course, with possible local recurrence due to incomplete/marginal excision



  • Nevertheless, metastatic risk is absent when confined to dermis



  • Needs to be distinguished/separated from leiomyosarcoma arising predominantly in the subcutis due to more aggressive biological behavior of the latter (see corresponding section)



Clinical features


Epidemiology





  • Males predominantly affected (M:F = 2–4:1)



  • Although the age distribution is wide, about 90% of the patients are older than 40 years



  • Extremely rare in childhood



  • Most common in the sixth decade of life



Presentation





  • Solitary, slowly growing nodule or indurated plaque



  • The majority appear to be asymptomatic, rare lesions painful



  • Size usually less than 2 cm



  • Predilection for trunk and lower extremities, followed by the head and neck and upper extremities



  • Isolated examples developed in the background of traumatic injury, ionizing radiation, lupus vulgaris, smallpox and scrofuloderma scar, tattoo, nevus sebaceous, and chronic venous ulcer



Prognosis and treatment





  • Status of resection margins the most important predictive factor for local recurrence(s)



  • Complete wide surgical excision generally curative, with very low risk of possible local recurrence



  • Recurrence rate about 20% after incomplete/marginal excision, multiple recurrences possible



  • Recurrent tumors can display increased cellularity and deeper localization



Pathology


Histology





  • Pure dermal-based proliferation, occasionally with very limited extension into the subcutis, generally of less than 5 mm in thickness



  • Infiltrative/poorly defined (diffuse) and/or nodular growth pattern



  • Intersecting fascicles of spindle cells ramifying between dermal collagen fibers




    • Nuclear atypia mild to moderate, can be severe on occasion



    • Nuclei cigar shaped or blunt ended with abundant eosinophilic cytoplasm



    • Mitoses present, usually from 2 to 5 mitoses per 10 high-power fields, but their number can vary greatly among lesions



    • Atypical mitoses not uncommon (in up to 50% of lesions)



    • Eccentric perinuclear intracytoplasmic vacuoles occasionally present



    • Tumoral necrosis rare (in less than 5% of the lesions), generally focal



    • Multinucleated giant cells few and scattered




  • A tumor-free, subepidermal grenz zone of variable thickness present in the majority of the lesions



  • Additional occasional histological features




    • Focal epithelioid cell morphology



    • Granular cell change



    • Myxoid stromal degeneration and hyalinization/sclerosis



    • Multinucleated osteoclast-like giant cells



    • Perivascular inflammatory cell infiltrate composed of lymphocytes and histiocytes




  • Desmoplastic variant of leiomyosarcoma




    • Predominance of hyalinized/sclerotic stroma over neoplastic cells




Immunohistochemistry/special stains





  • Smooth muscle actin, calponin, desmin, and h-Caldesmon positive in decreasing order of frequency



  • Up to 50% display focal cytokeratin positivity



  • Rare examples with focal S100 protein positivity also reported



Main differential diagnoses





  • Pilar leiomyoma



  • Cellular fibrous histiocytoma



  • Nodular fasciitis



  • Sarcomatoid carcinoma


Fig. 1


Cutaneous leiomyosarcoma.

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Oct 29, 2019 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Cutaneous smooth muscle tumors
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