Benign Soft Tissue Tumors



Benign Soft Tissue Tumors


Timothy A. Damron

Gustavo De La Roza



Benign soft tissue tumors outnumber soft tissue sarcomas by approximately 100:1. In adults, lipomas are the most common soft tissue tumor; in children, hemangiomas are the most common. Recognition of these relatively more common benign tumors is important not only to avoid overtreatment but also to allow distinction from their malignant counterparts. Soft tissue tumors, both benign and malignant, are classified according to the purported cell of origin or resemblance, and the organization of this chapter will follow the latest World Health Organization (WHO) scheme in that regard.


Fatty Benign Soft Tissue Tumors


Lipoma

Lipoma is the most common soft tissue tumor in adults. However, because it is, soft tissue sarcomas are sometimes assumed to be lipomas, unnecessarily delaying the diagnosis. Hence, recognition of the distinction between benign lipomas and soft tissue sarcomas is very important.


Pathogenesis and Pathophysiology



  • Etiology is unknown.


  • More common in obese patients


  • Peak age: 40 to 60 (rare in children)


  • Multiple lipomas in 5%


Histopathology



  • Lobules of mature adipocytes


  • Occasionally other areas of tissue formation



    • Bone = osteolipoma


    • Cartilage = chondrolipoma


    • Myxoid change = myxolipoma


Genetics



  • Chromosomal aberrations in up to 75%


  • Three patterns



    • 12q13-15 aberrations


    • 6p21-23 aberrations


    • Loss of material from 13q


Classification



  • Histologic variant subtypes have no prognostic significance.


  • Infiltrative



Intermuscular Versus Intramuscular



  • Intermuscular: easily shelled out between muscles


  • Intramuscular: two types within muscle



    • Well demarcated


    • Infiltrative: infiltrates and encases atrophic muscle fibers


Lipoma Arborescens



  • Subsynovial located lipoma


  • One type of intra-articular lipoma


Diagnosis


Clinical Features



  • Most common: painless mass with characteristic doughy feel


  • Most superficial lipomas are small (<5 cm).


  • Most deep lipomas are large (>5 cm).


  • Lipoma arborescens presents as articular swelling.


Radiologic Features



  • Superficial lipomas: difficult to see on radiographs or magnetic resonance imaging (MRI)


  • Deep lipomas (Fig. 11-1)



    • Fatty intramuscular shadow


    • Homogeneous fatty signal on all MRI sequences


    • No gadolinium enhancement


    • Occasional entrapped muscle fibers or fibrous strands


  • Lipoma arborescens



    • Fatty infiltration throughout affected synovium with fat-distended villi






Figure 11-1 Inramuscular lipoma of the proximal forearm. (A) The fatty soft tissue shadow is shown within the muscle of the proximal forearm by plain radiograph. Axial T1-weighted (B) and T2-weighted (C) MR imaging studies show homogenous fatty signal characteristics identical to that of the subcutaneous fat.


Diagnostic Work-up



  • Most superficial lipomas are distinguished by their doughy characteristics on physical examination and do not warrant radiographic evaluation.


  • Larger or deep masses warrant plain radiographic and MRI evaluation, which is usually diagnostic.


  • Biopsy is rarely indicated.


  • Also see Chapter 2, Evaluation of Soft Tissue Tumors.


Treatment


Surgical and Nonoperative Options



  • Superficial lipomas



    • Observation favored


    • Excision only if symptomatic


  • Deep lipomas



    • Observation if radiology identifies clearly as benign lesion (not atypical lipoma or liposarcoma)


    • Excision for most


Surgical Goals and Approaches



  • Marginal excision (complete excision through pseudocapsule)


  • Avoid transaction of nerves running within deep lipomas (piecemeal excision preferred).


Results and Outcome



  • Rarely recur following marginal excision


Lipomatosis

Lipomatosis is a diffuse systemic or regional overgrowth of mature adipose tissue that differs from normal fat only in
its distribution. Lipomatosis should be distinguished from lipomas, as the former conditions may be correctable by addressing the underlying condition and tend to recur after attempted excision.


Pathogenesis and Pathophysiology



  • Etiology is poorly understood.


  • Possibly due to point mutations in mitochondrial genes


  • See Table 11-1 for epidemiology.


  • Histopathology: mature fat in poorly circumscribed lobules or sheets infiltrating surrounding tissues


Classification



  • Classified by distribution for idiopathic types (diffuse, pelvic, symmetric) or by etiology (steroid, HIV lipodystrophy)


Diagnosis



  • Notable accumulations of fat in affected areas may resemble neoplasms (see Table 11-1).


  • Radiologic studies document extent of fatty deposition.


  • Neither radiological evaluation nor biopsy is usually necessary to diagnosis the lipomatoses.


  • See Chapter 2.


Treatment and Outcome



  • Palliative surgery is rarely indicated unless life-threatening fat accumulation (such as that causing laryngeal compression in Madelung’s disease).


  • Correction of steroid lipomatosis follows lowering of steroid levels.








Table 11-1 Epidemiology and Clinical Features of Lipomatosis Subtypes
































Subtype Epidemiology Distribution Potential Complications or Associated Symptoms
Diffuse Typically <2 yr Trunk, large part of extremity, head and neck, pelvis, or intestinal
Macrodactyly or digital gigantism		  
Pelvic Black males all ages, 9 yr and up Perivesicular, perirectal Bowel or bladder symptoms (frequency, constipation), perineal/abdominal/low back pain
Symmetric (Madelung’s disease) Middle-aged men of Mediterranean descent Upper body, especially neck Cranial or peripheral neuropathy
Airway obstruction
Superior vena cava syndrome
Associated with alcoholism, hyperuricemia, hyperlipidemia
Steroid Steroid treatment
Primary adrenal cortical axis overstimulation		 Facial, sternal, or buffalo hump Secondary manifestations of hypercortisolism
HIV lipodystrophy HIV patients on treatment Visceral, breast, cervical fat
Fat wasting in face and limbs		 Associated with hyperlipidemia, diabetes


Lipomatosis of Nerve (Lipofibromatous Hamartoma)

Lipofibromatosis, also referred to variously as lipofibromatous hamartoma, fibrolipomatosis, and intraneural lipoma, among other names, is a fatty and fibrous infiltrative process affecting the epineurium and leading to enlargement of the affected nerve. The median and ulnar nerves are most commonly affected.


Pathogenesis and Pathophysiology



  • Etiology is unknown.


  • Peak age: 10 to 40


  • Frequently evident at birth or early childhood


  • Female > male if macrodactyly present; male > female if none


  • Gross histopathology: yellow fibrofatty infiltration of nerve (Fig. 11-2)


  • Microscopic histopathology: epineurial and perineural fibrofatty infiltration isolating individual nerve bundles


Diagnosis


Clinical Features



  • Gradually enlarging mass with variable neurologic deficits


  • Median nerve or branches > ulnar nerve


  • Foot, brachial plexus less common sites


  • Macrodactyly in one third







Figure 11-2 A Fibrous hamartoma of infancy. Organoid pattern composed of intersecting fascicles of spindle cells separated by collagen, mature fat, and islands of immature mesenchymal cells with myxoid matrix. B Close-up view of characteristic island of immature mesenchyma in fibrous hamartoma of infancy.


Radiologic Features



  • MRI findings pathognomonic



    • Fusiform neural enlargement following branching pattern of nerve


    • Hypointense serpentine nerve bundles on both T1- and T2-weighted images


    • Variable intramuscular fatty deposition


Diagnostic Work-up



  • Because MRI is diagnostic, biopsy is usually not needed.


Treatment



  • Goal of surgical intervention is to decompress nerve if symptomatic.


  • Avoid attempted excision, which may damage nerve.


Lipoblastoma

Lipoblastoma is a tumor resembling fetal adipose tissue that occurs predominately in infants and may be localized (lipoblastoma) or diffuse (lipoblastomatosis). Since lipomas generally do not occur in this age group, lipoblastoma should be considered highly in the differential diagnosis of any tumor with fatty imaging characteristics in a child.


Pathogenesis and Pathophysiology



  • Etiology is unknown.


  • Peak age: birth to age 3; less common in older children


  • Males > females


Histopathology



  • Variable mixture of mature adipocytes and immature fat cells (lipoblasts)


  • Variable myxoid background with plexiform vascular pattern suggestive of myxoid liposarcoma


  • Pronounced lobular pattern and lack of atypia distinguishes lipoblastoma from liposarcoma


Genetics



  • 8q11-13 rearrangement in most cases


  • Fusion gene products: HAS2/PLAG1, COL1A2/PLAG1


Classification



  • Solitary (lipoblastoma) versus diffuse (lipoblastomatosis)


Diagnosis



Clinical Features



  • Sites: extremities predominate


  • Typically small (2 to 5 cm), superficial mass


  • Lipoblastomatosis often involves muscle as well.


Radiologic Features



  • Fatty signal characteristics



    • Bright on T1-weighted MRI, dark on fat-suppressed sequences, identical to surrounding fat


  • Indistinguishable from lipoma, well-differentiated liposarcoma (atypical lipoma) by radiology


Treatment and Outcome



  • Lipoblastoma: marginal en bloc excision


  • Lipoblastomatosis: wide surgical excision


  • Recurrence rare in lipoblastoma; up to 22% in lipoblastomatosis









Table 11-2 Histological Lipoma Variants






































Tumor Peak Ages/ Gender Distribution Clinical Features Histology
Angiolipoma Late teens to early 20s
Rare >50 yr		 Forearm > trunk > upper arm
Superficial		 Small
Frequently multiple
Painful mass		 Mature adipocytes
Branching capillary-sized vessels (see Fig. 11-3)
Chondroid lipoma Adults
Female:male 4:1		 Proximal extremities or limb girdles > trunk
Deep or involving fascia		 Painless mass
Half with enlargement		 Nests and cords of lipoblasts embedded in myxoid or hyaline cartilage matrix
Spindle cell lipoma Adults 45 to 65 yr
Male:female 9:1		 Posterior neck and shoulder > upper arm
Superficial		 Small
Rarely multiple		 Adipocytes, spindle cells, and collagen bundles
Variable inflammatory cells (especially mast cells)
Pleomorphic lipoma Adults >45 yr
Male:female 9:1		 Posterior neck and shoulder > upper arm
Superficial		 Small
Rarely multiple		 Spindle cells and giant cells with nuclei arranged in “floret-like” pattern
Hibernoma Young adults
20 to 40 yr (60%)		 Thigh > trunk > upper extremity > head and neck
Subcutaneous > deep (9:1)		 Painless mass
Enhances with MRI contrast		 Polygonal brown fat cells
Lipoblast-like multivacuolated cells (see Fig. 11-4)


Histologic Lipoma Variants

The histologic variants of lipoma are summarized in Table 11-2, and examples are shown in Figures 11-3 and 11-4.


Fibroblastic Benign Soft Tissue Tumors


Nodular Fasciitis

Nodular fasciitis is a tumor predominately of the upper extremity and neck region that is distinguished by its rapid growth and its tissue culture–like histology pattern.


Pathogenesis and Pathophysiology



  • Etiology: unknown, but history of trauma common


Epidemiology



  • Peak age: young adults, but may involve any age


Histopathology (Fig. 11-5)



  • Plump, regular myofibroblasts


  • Frequent mitoses but not atypical mitoses


  • Tissue culture–like, “torn” or “feathery” appearance at low power


  • Prominent small vessels may resemble granulation tissue.


  • Nodular infiltrative pattern of organization


  • Extravasated red blood cells, chronic inflammatory cells, and even giant cells may be seen.


  • SMA and MSA positive


  • Desmin, cytokeratin, and S100 negative






Figure 11-3 Angiolipoma composed of mature adipose tissue intermixed with numerous vascular channels. The vascularity is often more prominent in subcapsular areas.







Figure 11-4 Hibernoma: rare fatty tumor composed of mature adipose tissue and a large number of multivacuolated brown fat cells with abundant granular cytoplasm and a centrally located nucleus.


Genetics



  • Some clonality suggesting neoplastic nature demonstrated, but may represent artifact of culture conditions


Diagnosis



Clinical Features



  • Subcutaneous >> intramuscular


  • Upper extremity, trunk, head and neck most common


  • Rapid growth is characteristic.


  • Clinical history usually <1 to 2 months


  • Pain and local tenderness common


  • Small size, usually <2 cm






Figure 11-5 Nodular fasciitis: cellular proliferation of stellate cells with vague storiform pattern and extravasated red blood cells. Inflammatory cells and mitoses are also commonly seen, but there is no cytologic atypia.


Radiologic Features



Treatment and Outcome



  • Marginal excision


  • Rare recurrence should warrant reconsideration of diagnosis.


Proliferative Fasciitis and Myositis

These two processes are similar to nodular fasciitis in their rapid growth, predilection for the upper extremity, and plump myofibroblastic cells, but they are distinguished by the large ganglion-like cells that are also present. Proliferative fasciitis (PF) involves the fascia, while proliferative myositis (PM) involves the muscle.


Pathogenesis and Pathophysiology



  • Etiology is unknown, although a history of trauma may be elicited.


  • Peak age: middle-aged or older adults, older than nodular fasciitis


  • Much less common than nodular fasciitis


Histopathology



  • Two cellular types: plump myofibroblasts and ganglion-like cells


  • Plump myofibroblasts resemble those of nodular fasciitis.


  • Ganglion-like cells: large with one to three rounded nuclei, prominent nucleoli, and abundant cytoplasm


  • Numerous mitoses but not atypical mitoses


  • Infiltrative growth pattern (along fascial planes for PF and between muscle groups in PM)


  • Checkerboard pattern of infiltration between muscle fibers for PM


  • SMA and MSA positive


  • Desmin, cytokeratin, and S100 negative


Genetics



  • Similar to nodular fasciitis


Diagnosis



Clinical Features



  • PF: upper extremity (especially forearm) > lower extremity > trunk


  • PM: trunk > shoulder girdle > upper arm > thigh


  • Rapid growth is characteristic.







    Figure 11-6 Nodular fasciitis of the shoulder. (A) The patient presented with a 3-week history of a rapidly enlarging, painful soft tissue mass over the anterior deltoid. Sagittal MR studies show nonspecific findings of a heterogeneous intramuscular mass hypointense to muscle on T1-weighted sequences (B), hyperintense on T2-weighted images (C), and enhancing on post-gadolinium sequences (D).



  • Clinical history usually <1 or 2 months


  • Pain and local tenderness more common with PF


  • Small size, usually <5 cm


Radiologic Features



  • Nonspecific soft tissue mass


Treatment and Outcome



  • Marginal excision


  • Recurrence is rare.


Myositis Ossificans

Myositis ossificans is a benign reparative process characterized by bone formation within the soft tissues in response to trauma. On the one hand, it may simulate malignancy, but conversely, sarcomas that give a similar appearance may be mistaken for this benign, self-limited condition.


Pathogenesis and Pathophysiology



  • Trauma history elicited in up to 75% of patients; repetitive trauma in others


  • Peak age: young, physically active adults (rare in infants or elderly)


  • Males > females


Histopathology



  • Zonal proliferation with central fibroblasts and peripheral osteoblast-rimmed bone trabeculae


  • Progression from initially fibrous tissue to peripheral woven bone and then eventually lamellar bone


  • Peripheral ossification usually evident by 3 weeks


  • Mitoses frequent but no atypical mitoses


Diagnosis



Clinical Features



  • Initial 1 to 2 weeks after injury: swollen, tender


  • From 2 to 6 weeks after injury: tenderness and pain resolve, and painless, very firm mass forms


  • Chronically, the mass becomes less prominent over time.


  • Any location in body susceptible to trauma


  • Most common locations: thigh, shoulder, buttock, elbow


Radiologic Features



  • Initial 1 to 2 weeks after injury: x-ray, computed tomography (CT), MRI shows soft tissue shadow, heterogeneous MRI signal with edema


  • From 2 to 6 weeks after injury: x-ray, CT best show peripheral rim of calcifications (Fig. 11-7)


  • Chronically, MRI eventually shows low-signal rim with fatty marrow signal centrally.


Treatment and Outcome



  • Observation is best, but marginal excision is appropriate if sufficiently symptomatic.


  • May recur if excised incompletely early in course


Elastofibroma

Elastofibroma (elastofibroma dorsi) is a unique process that occurs almost exclusively in a subscapular location in adults and is characterized by histologic evidence of elastic fibers.


Pathogenesis and Pathophysiology



  • Etiology is unknown, although repetitive trauma has been implicated.


  • Peak age in seventh and eighth decades (nearly always after age 50)


  • Females > males


Histopathology



  • Low-cellularity collagenous tissue with intermixed elastic fibers (Fig. 11-8)


  • Immunohistochemistry positive for elastin


Genetics



  • Familial occurrence reported in Okinawa


Diagnosis


Clinical Features



  • Slowly growing mass, typically painless and nontender


  • May cause popping scapula or local discomfort


  • Classic location



    • Nearly exclusively subscapular, applied to chest wall at the lower portion of the scapula


    • Deep to latissimus dorsi and rhomboid major


    • Often attached to periosteum of ribs


    • Rare musculoskeletal sites: upper arm, hip


    • May be bilateral (especially subclinical) in up to one third


Radiologic Features



  • Fibrous and fatty elements create layered picture.


  • MRI may be highly suggestive (Fig. 11-9).



    • Fatty areas: bright areas on T1-weighted images, intermediate on T2-weighted images


    • Fibrous areas: similar to muscle


Diagnostic Work-up



  • Biopsy is generally recommended to confirm diagnosis, although the combination of classic location and radiologic appearance is highly suggestive.


  • Also see Chapter 2.







Figure 11-7 (A) Initial plain radiographs within the first 2 to 3 weeks may not show the characteristic peripheral rim of calcification associated with myositis ossificans. (B) Subsequently, the peripheral rim is best demonstrated on computed tomography. (C) MR studies show a heterogeneous mass that is sometimes confused with a soft tissue sarcoma.


Treatment and Outcome



  • Marginal excision indicated for symptomatic patients but may be observed if asymptomatic and histologically proven


  • Rarely recurs after complete excision


Superficial Fibromatoses

The superficial fibromatoses include palmar fibromatosis (Dupuytren’s disease or contracture) and plantar fibromatosis (Ledderhose disease), both fibroblastic proliferations with infiltrative growth that are usually easily recognizable clinically and have a high rate of local recurrence if excised.


Pathogenesis and Pathophysiology



  • Etiology is multifactorial.



    • Familial component


    • Trauma


    • Associated diseases: epilepsy, diabetes, alcohol- induced liver disease


  • Peak age: adults with increasing frequency in advanced ages (rare before age 30)


  • Males >> females (3 to 4:1)


  • Ethnicity: highest incidence in northern Europe and in
    those of northern European descent; rare in non-Caucasians


  • Pathophysiology is shown in Figure 11-10.






Figure 11-8 (A) Elastofibroma composed of intertwining, swollen collagen and elastic fibers with fibroblasts. (B) Elastic fibers highlighted by EVG stain in elastofibroma.


Diagnosis


Clinical Features

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Jul 21, 2016 | Posted by in ONCOLOGY | Comments Off on Benign Soft Tissue Tumors

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