Nonodontogenic intraosseous tumors and inflammatory/reactive conditions

Clinical and radiographic findings

• Tori: These occur in 10% to 30% of adults and present as exophytic, hard, uninodular or multinodular bony masses covered by mucosa. Torus palatinus is more common and is located on the midline of palate while torus mandibularis occurs on the lingual mandible and tends to be bilateral and symmetric; they may grow to a large size ( Fig. 17.1 A–B). They are readily traumatized and ulcerated because of their protuberant nature or may exhibit frictional keratosis and ulceration; 2% of patients have both palatal and mandibular tori. Mandibular tori appear as radiopacities in dental films.

  

• Exostosis: This occurs in up to 27% of adults with a 5:1 male predilection and presents as an outgrowth of bone, polypoid, sessile, or shelf-like, frequently on buccal aspects of the mandible, maxilla, or ascending arch of the palate, with more than 90% of cases having concurrent tori ( Fig. 17.1 C–D); exostoses may show rapid growth in some patients. They appear as radiopacities in dental films.

• Subpontic osseous hyperplasia (subpontic exostosis): This is an outgrowth of bone beneath a pontic (artificial tooth on a bridge that replaces a missing tooth) that generally develops more than 10 years after placement of the fixed prosthesis. It causes discomfort in approximately 12% of patients, and radiographically is indistinguishable from normal bone, although there may be some osteosclerosis ( Fig. 17.1 E).

• Osteoma: Periosteal osteoma arises from the surface of the bone and causes a noticeable mass either in the oral cavity or palpable on the skin overlying the mandible where it is more prevalent ( Fig. 17.1 F). Endosteal osteomas are asymptomatic and noted incidentally on radiographs as round or ovoid homogeneous radiopacities without a surrounding radiolucent rim ( Fig. 17.1 G). Large ones may displace tooth roots. Sino-orbital osteomas affect the maxillary sinus in approximately 10% of cases.

Etiopathogenesis and histopathologic features

Tori are inherited in an autosomal dominant fashion and may exhibit ethnic differences. Exostoses may develop as a result of genetic and environmental factors and some have suggested that parafunctional habits such as bruxing play a role. Subpontic osseous hyperplasia results from irritation of bone beneath the pontic, leading to bone deposition. Multiple osteomas are associated with familial adenomatous polyposis syndrome which is an autosomal dominant condition associated with mutation in APC ( Fig. 17.1 H). This syndrome is also associated with the development of supernumerary teeth and odontomas, colonic polyps that develop in childhood and adolescence that are highly associated with the development of colorectal carcinoma at a young age, desmoid tumors, fibromas, thyroid carcinomas, hepatoblastoma, pancreatobiliary tumors, nasopharyngeal angiofibromas, retinal pigmentary disorder, and epidermoid cysts. Gardner syndrome is one variant of this syndrome.

• Tori, exostoses, osseous hyperplasia, and osteomas have similar histopathology. There is dense lamellar bone with well-spaced small osteocytes within lacunae, variable fibrosis, and usually inconspicuous osteoblastic rimming, unless inflamed; fatty marrow is often present ( Fig. 17.2 A–B). Lamellar bone is characterized by long, sweeping collagen bundles viewed through polarized light ( Fig. 17.2 C).

  

• Sino-orbital osteomas may show osteoblastomatous foci.

Differential diagnosis

• Osteochondroma occurs mostly on the coronoid and condylar processes in young adults and because of its location may cause swelling and trismus. It appears as a nodule of bone with a benign cartilaginous cap. Coronoid osteochondromas have been reported in patients with hereditary multiple exostoses syndrome , an autosomal dominant condition caused by mutations in EXT1 that produces exostosin-1 and exostosin-2 that are involved in the development of multiple osteochondromas in the long and flat bones.

Management and prognosis

• Excision is performed usually in preparation for denture fabrication, or if the lesion is constantly ulcerated from trauma.

Clinical findings and radiographic

• Condensing osteitis: This occurs in 1% to 6% of the population and there is an asymptomatic poorly demarcated but discrete homogeneous radiopacity seen around the apices and roots of teeth. These are usually mandibular premolars and molars that are nonvital and have been endodontically treated. Widening of the periodontal ligament space should raise the suspicion that the associated tooth is nonvital ( Fig. 17.3 A–B).

  

• Idiopathic osteosclerosis (dense bone island, bone scar): This occurs in approximately 1% to 6% of the population and may be more prevalent in women, especially in the East Asian population. It presents as an asymptomatic poorly demarcated but discrete radiopacity that is usually not located at the apices of teeth. It occurs in the mandible in greater than 80% of cases usually in the premolar–molar area, is discovered on routine radiography, and is unassociated with pain or swelling. If associated with apices of teeth, vitality testing of teeth should be performed ( Fig. 17.3 C–D).

Etiopathogenesis and histopathologic features

Condensing osteitis likely is caused by inflammation of odontogenic origin (usually from a nonvital tooth) leading to reactive bone formation and sclerosis. Idiopathic osteosclerosis is of unknown etiology.

• Both have similar histopathology and exhibits densely sclerotic bone with few or small Haversian canals; fibrosis, fatty marrow, and mild chronic inflammation may be present ( Fig. 17.3 E).

Differential diagnosis

• Endosteal osteoma may appear similar to idiopathic osteosclerosis and condensing osteitis although in reactive conditions, the radiopacity tends to have an irregular shape rather than being round or ovoid. In either case, no treatment is necessary except for evaluation for familial adenomatous polyposis syndrome when multiple osteomas are present.

Management and prognosis

• Biopsy is not necessary if the lesion is recognized for what it is on the radiograph. When idiopathic osteosclerosis occurs at the apices of teeth not previously endodontically treated, the teeth should be evaluated for vitality.

Clinical findings and radiographic

• Suppurative osteomyelitis , acute and chronic: This usually occurs in adults and is associated with a chronic tooth infection either of pulpal or periodontal origin, postextraction of infected teeth, or a poorly healed jaw fracture ( Fig. 17.4 A). There is pain and swelling, and suppuration and sinus tracts may be present with some symptom-relief when there is drainage.

  • Patients with focal or multifocal cementoosseous dysplasia with sclerotic avascular cementoosseous masses are at risk for developing such osteomyelitis ( Fig. 17.4 B).

  

• Chronic nonbacterial osteomyelitis:

  • The majority (>95% of cases) occur before age 20 with a 2:1 female predilection, and there is intermittent pain, swelling, trismus, and intermittent fever with little response to antibiotics ( Fig. 17.4 C). The mandible is one of the bones commonly affected, together with metaphases of long bones, vertebra, and clavicles. Patients often begin with involvement of one bone and approximately 80% develop involvement of other bones (CRMO). Patients may exhibit acne, palmar-plantar pustulosis, inflammatory arthritis, and other autoinflammatory conditions such as psoriasis and inflammatory bowel disease although this is more common in adults with SAPHO syndrome who more frequently exhibit involvement of the sternum and clavicle.

  • Radiographs show diffuse expansion of the mandible with a ground-glass appearance, osteosclerosis, and small osteolytic foci ( Fig. 17.4 D).

  • Normal complete blood count, and elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) and abnormal radiographic findings are key to the diagnosis.

• Osteonecrosis:

  • This presents as bony sequestrum, usually exposed, with or without pain ( Fig. 17.5 A–D). In the case of medication-related osteonecrosis, chronic sinus tracts and nonhealing extraction sockets present for more than 6 months and usually years after tooth extraction are common manifestations. Radiographs reveal thickened lamina dura, osteosclerosis, and persistent extraction sockets, with advanced cases exhibiting mottled radiolucency and radiopacities consistent with sequestra ( Table 17.2 ; Fig. 17.5 E–F).

    

• Benign spontaneous sequestration of the lingual plate:

  • This occurs in healthy individuals in the fourth to sixth decades, with a 1.8:1 male predilection, and consists of small, 0.1 to 1.0 cm sequestra noted on the mylohyoid ridge ( Fig. 17.5 G). These heal spontaneously after the sequestrum exfoliates or is removed. There is no underlying radiolucency.

Etiopathogenesis and histopathologic features

Suppurative osteomyelitis is caused by a bacterial infection from a tooth or nonhealing fracture site. Most cases (66%) are polymicrobial although streptococcus viridans is the most commonly isolated organism. Primary nonbacterial sclerosing osteomyelitis of the mandible in children and adolescents is an autoinflammatory rheumatologic condition that is likely caused by persistent activation of the innate immune system pathways in a susceptible host, and is the monostotic form of CRMO that usually affects the lower limbs, pelvis, and clavicle with skin lesions as noted earlier. SAPHO syndrome is the adult equivalent. Causes of osteonecrosis include suppression of bone turnover especially by medications used to treat osteoporosis and cancer involving the bone which includes antiresorptive medications, antiangiogenic medications, some tyrosine kinase inhibitors, and other targeted therapies. Vascular compromise, trauma, and infection are important contributing factors (see Table 17.2 ).

• Small pieces of sequestra exteriorize naturally when it lies near the surface of the bone and epithelium grows downward and together with granulation tissue, separates the sequestrum from the underlying vital bone; this process also applies to failed bone grafts ( Fig. 17.6 A–B).

  

• Suppurative osteomyelitis: There are nonviable bony sequestra and granulation tissue with acute and chronic inflammation and abscesses; a sclerotic mass of nonvital globular sclerotic cementoosseous material may be present if there is a preexisting cementoosseous dysplasia (see Fig. 17.6 C–D).

• Chronic nonbacterial osteomyelitis: The reactive and reparative osteoid forms parallel bone trabeculae or exhibit an interlacing pattern. There is prominent stromal fibrosis, mild to insignificant chronic inflammation, dilated sinusoidal vessels, and rarely sequestrum. Other features include a fibrous dysplasia–like pattern and atypical osteoid formation ( Fig. 17.7 ).

  

• Osteonecrosis of other etiologies including osteoradionecrosis: There are nonviable bony sequestra with empty lacunae and ragged resorptive defects, often with extensive bacterial colonization especially with Actinomycetes species within the biofilm ( Figs. 17.8 and 17.9 ). A diagnosis of actinomycosis (actinomycotic osteomyelitis) should be made only if sulfur granules are present, surrounded by suppuration with Splendore-Hoeppli effect resulting from host reponse to the bacteria ( Fig. 4.3 C–D); Eikenella corrodens is often present. Osteoclasts may be seen, often detached from the surface of the sequestra in bisphosphonate-associated osteonecrosis, and there may be extensive pseudoepitheliomatous hyperplasia ( Fig. 17.10 ).

  
  
  

Differential diagnosis

• Atypical osteoid and fibrous dysplasia–like areas in chronic nonbacterial osteomyelitis must always be correlated with the clinical findings; an incorrect diagnosis of fibrous dysplasia or osteosarcoma may be rendered when these features are taken out of context and especially if the biopsy is small.

• A search should be made for primary bone malignancy (such as myeloma) or metastatic disease for patients with cancer who develop medication-related osteonecrosis.

• Recurrent squamous cell carcinoma is a consideration for the pseudoepitheliomatous hyperplasia often noted adjacent to osteoradionecrosis.

• Bone graft material (such as freeze-dried bone) presents as fragments of necrotic bone and can be differentiated from native sequestra by the regularity in shape and size and even distribution of the osseous particles; it also shows appositional host bone on the surface in most cases ( Fig. 17.11 ).

  

Management and prognosis

• Suppurative osteomyelitis: Sequestrectomy and debridement, long-term antibiotics (β-lactams and clindamycin), and hyperbaric oxygen are recommended treatments.

• Chronic nonbacterial osteomyelitis: Treatment is with nonsteroidal antiinflammatory drugs, corticosteroids; anti–tumor necrosis factor alpha (TNFα) inhibitors, and bisphosphonates. Relapse is common.

• Medication-related osteonecrosis: Nonviable bone is often readily removed by nonsurgical sequestrectomy or dislodgement, surgical sequestrectomy and debridement, or resection and antibiotics depending on the stage ( Table 17.2 ; Fig. 17.12 ); hyperbaric oxygen may be useful in severe cases. However, in patients on antiresorptive therapies or anticancer therapies, osteonecrosis may not completely resolve because of the need for patients to be on such therapies. Treatment is directed towards relief of symptoms and prevention of infections.

  

Clinical findings and radiographic

• Craniofacial lesions are generally detected within the first decade of life in 90% of patients as painless or painful unilateral swelling of the maxilla and midface. Most cases (70%–90%) are monostotic and the maxilla and craniofacial bones are the most commonly affected. There may be malocclusion as the jaw expands and displacement of the orbital floor leads to visual impairment while involvement of skull base foramina results in nerve-specific neural symptoms. The monostotic form has no sex predilection.

• The term “craniofacial fibrous dysplasia” is applied when lesional tissue involves contiguous facial bones crossing suture lines.

• The polyostotic form is seen in McCune-Albright syndrome, tends to occur in females, and affects the craniofacial region. Patients tend to be younger, have more pain, pathologic fractures, and visual disturbances. They present with café au lait pigmentation with irregular borders (coast of Maine morphology) and hyperfunctioning endocrine abnormalities such as precocious puberty, diabetes mellitus, and thyroid disease. In Mazabraud syndrome, patients also develop soft tissue myxomas.

• Lesions persist throughout life and pregnancy may cause exacerbation.

• Radiographically, there is a diffuse, homogenous, ground-glass appearance to the bone that merges with the cortex ( Fig. 17.13 ). There is loss of lamina dura and in the mandible, the inferior alveolar canal may be displaced in long-standing lesions. Long-standing lesions appear more heterogenous with areas of radiolucency. Teeth exhibiting taurodontism may be present.

• Cases of regional odontomaxillary dysplasia and even segmental odontodysplasia may appear similar ( Fig. 17.13 C and Fig. 17.14 ).

  

Etiopathogenesis and histopathologic features

Fibrous dysplasia and McCune-Albright syndrome are associated with an activating missense mutation in GNAS that results in activation of bone marrow stromal cells that have impaired ability to differentiate towards osteoblasts, hematopoietic marrow or adipocytes leading to deposition of fibroosseous tissue only.

• There is a proliferation of spindle cells and delicate fibrocollagenous tissue and thin, interconnected curvilinear trabeculae of woven bone (taking the form of the letters “Y,” “U,” or “C”) in early lesions, or thicker and denser trabeculae of woven or lamellar bone in older lesions. The thin, delicate, spicules forming “Chinese characters” are more often seen in lesions of the appendicular and axial skeleton. Osteoblastic rimming and occasional osteoclasts may be seen focally, especially in early and inflamed lesions and there is variable vascularity ( Figs. 17.15 and 17.16 ). Peritrabecular clefting and cystic change may be present, but globular deposits of basophilic cementum-like material are rarely seen.

  
  

• Infrequently, aneurysmal bone cyst and giant cell lesions are noted within fibrous dysplasia.

Differential diagnosis

• Central cementoossifying fibroma radiographically is a well-delineated, sometimes corticated radiolucency with variable calcifications. The boney trabeculae are also not curvilinear and globular cementicles are often present. Lesions are negative for GNAS mutation.

• Low-grade osteosarcoma is differentiated by radiographic heterogeneity, and the proliferation of atypical osteoblasts in the fibrous stroma positive for MDM2 and CDK4.

Management and prognosis

• Surgical recontouring of the bone is often performed for cosmetic reasons although the bone continues to expand until growth slows after puberty; once stable, the quiescent lesions persist for the life of the patient.

• Patients should be evaluated for McCune-Albright syndrome if lesions are multifocal and patients with the syndrome tends to experience fractures and visual symptoms. Surgical decompression is indicated if there is impingement upon nerve foramina.

• Antiresorptive agents such as bisphosphonates and denosumab have not shown consistent success but may help with chronic pain.

• Malignant transformation occurs in less than 1% and 4% of monostotic and polyostotic/syndromic fibrous dysplasia, respectively. This generally takes the form of osteosarcoma, and less frequently chondrosarcoma. This should be suspected if lesions show rapid growth and expansion, and loss of the homogenous ground-glass appearance. Prior radiation therapy was noted in 25% of such patients.

Clinical and radiographic findings

• Trabecular variant: The majority of cases occur in the first and second decades of life with a mean age of 11 years and an age range of 1 to 33 years. There is equal sex distribution and there is equal involvement of the maxilla and mandible.

• Psammomatoid variant: This tends to occur in the second to fourth decades of life with a mean age of 18 years and a wider age range of 4 to 59 years. There is a 1.4:1 male predilection and the majority of cases are located in the paranasal sinuses and periorbital areas.

• Both variants exhibit a unilocular mixed radiolucent-radiopaque lesion with the psammomatoid variant often displaying a ground-glass appearance ( Fig. 17.17 ).

  

Etiopathogenesis and histopathologic features

Up to 70% of both tumors show amplification of MDM2 and RASAL1, but without overexpression of MDM2. The psammomatoid variant has shown fusion of breakpoints on Xq26 and 2q33.

• Both variants consist of a cellular proliferation of plump bipolar, spindle and stellate cells within delicately collagenous stroma, and infiltration of native bone may be seen.

  • Trabecular type:

  • Τhe fibrocollagenous tissue has a subtle fasciculated growth pattern and is more heterogenous than the psammomatoid variant. There is abundant osteoid and woven bone in single or interlacing trabeculae containing plump slightly atypical osteocytes with large ovoid nuclei and dispersed chromatin and small nucleoli; osteoblastic rimming is common, sometimes with multilayering of osteoblasts. Recapitulation of Sharpey fibers renders a trailing “paintbrush” appearance to the osteoid that surrounds bone trabeculae and the osteoid blends with the surrounding stroma. Zones of hypercellularity and hypocellularity with myxoid stroma are often noted. Hematoxyphilic acellular osteoid may be present and there are often clusters of multinucleated osteoclast-type giant cells surrounding fresh hemorrhage resulting in an aneurysmal bone cystlike ap pearance ( Figs. 17.18–17.20 ).

    
    
    

  • Psammomatoid type:

  • This is a more homogenous tumor with many basophilic, globular, or irregularly shaped ossicles, most of which are of uniform size with a few osteocytes within lacunae ( Fig. 17.21 ); these are uniformly dispersed throughout the tumor. These ossicles have a thin eosinophilic rim of osteoid and rarely exhibit osteoblastic rimming. In more advanced lesions, the ossicles fuse and form short trabeculae. Hematoxyphilic acellular spherical bodies resembling psammoma bodies may be present and aneurysmal bone cyst-like areas are seen in 10% to 30% of cases.

    

Differential diagnosis

• Central cementoossifying fibroma is an important differential for the trabecular variant but is much less cellular and generally more fibrous without the areas of myxoid change. Multinucleated osteoclast-type giant cells, hemorrhage and multilayering of osteoblasts on trabeculae are generally absent.

• Cementoosseous dysplasia is more similar in appearance to cementoossifying fibroma and typically is removed in small gritty fragments and has typical radiographic findings.

• Osteosarcoma will show a proliferation of atypical osteoblasts within the stroma with disorganized malignant osteoid, and sometimes cartilage, and cells are positive for MDM2 and CDK4.

Management and prognosis

• Most cases are treated with curettage, enucleation, and marginal or segmental resection, with curettage and enucleation significantly associated with while resection is not associated with recurrence.

• Recurrence rate is 20% to 30% for both variants with 75% of cases recurring within 2 years of treatment.

Clinical findings and radiographic

• Most cases occur in the first to third decades of life with 80% presenting before age 40. There is a painless swelling of the mandible which is involved in 70% to 75% of cases, usually in the anterior or body.

• There is a well-delineated radiolucency with 60% being unilocular. Cortical perforation occurs in 50% of cases and there may be tooth displacement and root resorption ( Fig. 17.22 A–B).

  

• The aggressive type is greater than 5 cm and recurs (two primary criteria), or shows at least three of the following secondary criteria: rapid growth, root resorption, tooth displacement, and thinning or perforation of the cortical plate ( Fig. 17.22 C–D).

• Multiple giant cell granulomas are sometimes seen in patients with neurofibromatosis type 1. Patients with Jaffe-Campanacci syndrome who present with café au lait macules, multiple giant cell granulomas of the jaws, nonossifying fibromas of long bones, cardiovascular malformations, intellectual disability, as well as other signs are now considered to be within the spectrum of neurofibromatosis type 1 because they exhibit mutation in NF1 .

Etiopathogenesis and histopathologic features

Mutation in TRPV4 is noted in 27% of cases and KRAS and FGFR1 in 16% of cases each. Such MAPK-pathway activation is the basis for RASopathies such as Noonan syndrome spectrum and neurofibromatosis type 1 that exhibit overlapping phenotypes and which are also associated with development of giant cell granulomas of the jaw. There is a multisystem disease that causes central giant cell granuloma of the jaw, skeletal abnormalities, and polyneuropathy associated with mutation in TRPV4, a channelopathy. The spindle cells in central giant cell granulomas of the jaws in patients with neurofibromatosis type 1 often exhibit mutations in NF1 . Central giant cell granuloma of the jaw lacks mutation in H3F3A that is commonly seen in giant cell tumors of long bones.

• There is a proliferation of spindled and epithelioid monocytic cells and clusters of multinucleated osteoclast-type giant cells with abundant fresh hemorrhage either in a diffuse or nodular pattern; siderophages and reactive osteoid and woven bone formation are often seen, and monocytic cells often show mitotic activity ( Figs. 17.23 and 17.24 ).

  
  

• Central giant cell granuloma is often noted in association with other conditions such as central cementoossifying fibroma and central odontogenic fibroma (see Chapter 15 ).

Differential diagnosis

• Brown tumor of hyperparathyroidism is indistinguishable from central giant cell granuloma; high parathormone levels and serum calcium differentiate between the two conditions.

• Multiple giant cell lesions may be seen in Noonan syndrome spectrum (formerly referred to as Noonan-like multiple giant cell lesion syndrome) where patients exhibit hypertelorism, down-slanting palpebral fissures, low-set ears, neck webbing, short stature, pectus excavatum, cardiac defects, and cryptorchidism; Noonan syndrome (one of the conditions within the spectrum) is associated with mutations in PTPN11 in 50% of cases in addition to mutations in SOS1 and RAF1 and other genes in the RAS-MAPK pathway. Lesions in patients with Noonan-like multiple giant cell lesion syndrome also exhibit mutations in PTPN11 and SOS1 confirming this syndrome is just a variant of Noonan syndrome.

• Aneurysmal bone cyst consists of large blood-filled spaces lined by multinucleated giant cells and most cases exhibit gene rearrangement associated with USP6 .

• Cherubism contains clusters of multinucleated giant cells and is distinguished by its typical bilateral presentation in a young child and is positive for mutation in SH3BP2 .

• Fibroosseous lesions exhibit abundant woven bone deposition but giant cells are usually only focally present.

Management and prognosis

• Curettage, enucleation, excision, resection, intralesional steroid injections, and calcitonin nasal spray may be employed with variable success.

• More recent treatments include enucleation and/or tumor debulking together with targeted therapies such as interferon-α, bisphosphonates, denosumab, and imatinib (see Fig. 17.25 ).

  

• Recurrence is noted in 8% to 23% of conventional nonaggressive cases and aggressive cases, respectively, depending on mode of therapy.

Clinical findings and radiographic

• The majority occur before the age of 20 years, and there is a slight female predilection. Patients develop swelling of the face (sometimes rapid) that may be painful, and the mandible is affected in 75% to 90% of cases.

• The lesion manifests as a well-delineated, unilocular, or, more often, multilocular (60% of cases) expansile radiolucency with a sclerotic rim of reactive bone and delicate intralesional septa ( Fig. 17.26 ); fluid level from hemorrhage is noted on imaging studies, and aspiration yields blood. Ten percent of lesions perforate the cortex.

  

• The lesion may occur concomitantly with fibrous dysplasia, fibrous dysplasia, ossifying fibroma, central giant cell granuloma, osteoblastoma, or other intraosseous neoplasms.

Etiopathogenesis and histopathologic features

Primary extracranial aneurysmal bone cysts, including the solid variant, show universal presence of USP6 rearrangement with a variety of fusion partners including CDH11 (the most common), as well as CNBP, COL1A1, CTNNB1, FOSL2, RUNX2, SPARC, FAT1, and many others. However, these rearrangements are not identified in secondary lesions, which may have a different etiology.

• Variably sized, sinusoidal blood-filled or empty spaces are surrounded by spindle mononuclear cells and multinucleated osteoclast-type giant cells. Fresh hemorrhage and siderophages are noted ( Fig. 17.27 ).

  

• Reactive or residual bone is a frequent finding and should not be overdiagnosed as a synchronous fibroosseous lesion. “Blue bone” from stromal calcifications is often noted.

• An aneurysmal bone cyst may be seen in association with other lesions, especially central giant cell granulomas, cementoossifying fibromas, fibrous dysplasias, and osteoblastoma in approximately 15% of cases ( Fig. 17.28 ).

  

• A solid variant exists composed of a proliferation of spindled fibroblasts and myofibroblasts in fascicles or with a storiform appearance, with very focal and subtle sinusoidal spaces, scattered osteoclasts, and reactive woven bone.