Juvenile granulosa cell tumor associated with Ollier disease.

Prior case reports have described synchronous ovarian juvenile granulosa cell tumor (JGCT) and enchondromatosis in patients with Ollier disease and Maffucci syndrome. We present a case of a juvenile granulosa cell tumor with an IDH1 somatic mutation identified in the ovarian tissue in a 15-year-old female who presented with abnormal vaginal bleeding, several months of irregular menses, and a large multicystic adnexal mass. Multiple mixed lytic and sclerotic lesions were identified in the bones of the pelvis on imaging studies obtained during the work-up of her abdominal mass. Like previous reports in patients with undiagnosed enchondromatosis, these lesions were presumed to represent skeletal metastases; however, biopsy tissue revealed a hyaline cartilage neoplasm. Subspecialty review of the imaging findings revealed imaging features classic for Ollier disease involving the flat bones of the pelvis. It is important for radiologists to be familiar with the association between enchondromatosis and JGCT. When a female patient with enchondromatosis presents with a large, unilateral, mixed solid-cystic ovarian mass, the diagnosis of JGCT can be suggested. Alternatively, when a patient is diagnosed with JGCT, any skeletal lesions should be scrutinized for imaging features that suggest a hyaline cartilage neoplasm to avoid the misdiagnosis of skeletal metastases in a patient with previously undiagnosed Ollier disease or Maffucci syndrome. To our knowledge, this is the second reported confirmed case of an IDH1 somatic mutation identified in the ovarian tissue of a JGCT in a patient with Ollier disease.

Imaging of spinal chordoma and benign notochordal cell tumor (BNCT) with radiologic pathologic correlation.

Benign notochordal cell tumor (BNCT) and chordoma are neoplasms of notochordal differentiation. BNCT represents notochordal rests, commonly an incidental lesion present in the spine in 19% of cadaveric specimens. BNCTs are often radiographically occult. CT of BNCT frequently reveals patchy sclerosis between areas of maintained underlying trabeculae. BNCT demonstrates marrow replacement on T1-weighted MR images with high signal intensity on T2-weighting. BNCTs are frequently smaller than 35 mm and lack significant enhancement, bone destruction, cortical permeation, or soft tissue components. Biopsy or surgical resection of BNCT is usually not warranted, although imaging surveillance may be indicated. Chordoma is a rare low-grade locally aggressive malignancy representing 1-4% of primary malignant bone tumors. Chordoma is most frequent between the ages of 50-60 years with a male predilection. Clinical symptoms, while nonspecific and location dependent, include back pain, numbness, myelopathy, and bowel/bladder incontinence. Unfortunately, lesions are often large at presentation owing to diagnosis delay. Imaging of chordoma shows variable mixtures of bone destruction and sclerosis, calcification (50-70% at CT) and large soft tissue components. MR imaging of chordoma reveals multilobulated areas of marrow replacement on T1-weighting and high signal intensity on T2-weighting reflecting the myxoid component within the lesion and areas of hemorrhage seen histologically. Treatment of chordoma is primarily surgical with prognosis related to resection extent. Unfortunately, complete resection is often not possible (21-75%) resulting in high local recurrence incidence (19-75%) and a 5-year survival rate of 45-86%. This article reviews and illustrates the clinical characteristics, pathologic features, imaging appearance spectrum, treatment, and prognosis of BNCT and spinal chordoma.

Chondroblastomas presenting in adulthood: a study of 39 patients with emphasis on histological features and skeletal distribution.

AIMS: Chondroblastomas (CB) are rare bone tumours that typically arise in the epiphysis/apophysis of long bones in skeletally immature patients. We explore the clinicopathological features of CB presenting in adults. METHODS AND RESULTS: CB in patients ≥20 years of age were retrieved from our institutional archives. Thirty-nine CB were identified (29 male/10 female; aged 20-54 years). Twenty (51%) cases occurred in long tubular bones, 10 (26%) in small bones of the feet, five (13%) in flat bones and four (10%) in the patella. All cases showed classic cytological features of CB, and chondroid matrix was universally present. Calcification was identified in 10 cases (26%), including various combinations of serpiginous (n = 7), punctate (n = 6), classic chicken-wire (n = 4) and psammomatous (n = 2) patterns. Haemosiderin (n = 19), woven bone (n = 13), secondary aneurysmal bone cyst formation (n = 8), foamy macrophages (n = 4), hyalinised vascular spaces (n = 2) and cholesterol clefts (n = 2) were noted. Follow-up information (n = 32, 1-452 months) revealed local recurrence in three patients, all >40 years of age with flat bone origin, one of which developed pulmonary metastases 132 months after initial diagnosis. CONCLUSIONS: CB in patients >20 years of age more frequently involves the short bones of the hands/feet and flat bones compared to those arising in their younger counterparts. A subset may harbour extensive serpiginous or psammomatous calcification rather than the classic chicken-wire pattern. Although the overall local recurrence rate in adulthood is approximately 10%, all three patients with recurrent disease had tumours involving flat bones, suggesting that tumours arising in these sites may behave more aggressively.

Unusual manifestations of diffuse-type tenosynovial giant cell tumor in two patients: importance of radiologic-pathologic correlation.

Diffuse-type tenosynovial giant cell tumor (TSGCT) is a rare, locally aggressive neoplasm. It most commonly occurs in the knee, followed by the hip, and has distinctive imaging features, including mass-like foci of low T2 signal intensity, "blooming" on gradient-echo MRI, and pronounced uptake on FDG PET/CT. Histologically, TSGCT demonstrates a neoplastic population of mononuclear cells admixed with hemosiderin-laden macrophages, foamy histiocytes, inflammatory cells, and osteoclast-like giant cells. In cases where diffuse-type TSGCT presents in an uncommon location or with atypical features, the imaging diagnosis may be challenging. Furthermore, because of its polymorphous appearance, it may be mistaken microscopically for other neoplastic and non-neoplastic histiocytic lesions. Herein, we present two cases of diffuse-type TSGCT presenting as large masses, and underscore the importance of radiologic-pathologic correlation for accurate diagnosis.

Chondrosarcoma arising within synovial chondromatosis of the lumbar spine.

Synovial chondromatosis is an uncommon benign neoplasm that usually affects large appendicular joints and only rarely the spine. There are only a few small series and case reports documenting malignant transformation of synovial chondromatosis into secondary chondrosarcoma, typically within the hip in the setting of recalcitrant disease and multiple recurrences. Chondrosarcoma arising in synovial chondromatosis of the spine is exceedingly rare, with only one previously published case report involving the craniocervical junction. We present a case of chondrosarcoma arising within synovial chondromatosis of the lumbosacral spine, with the diagnosis made at the time of initial presentation. We describe the clinical, imaging, and histopathological findings and review diagnostic criteria for this difficult diagnosis.

Adamantinoma of bone: Long-term follow-up of 46 consecutive patients.

BACKGROUND: Adamantinomas are rare bone tumors, commonly affecting the tibia. Due to the rare nature of disease, previous studies are small or from multiple centers. The purpose of this study is to investigate outcomes of patients with adamantinoma treated in a single institution. METHODS: Forty-six histological confirmed adamantinomas of the extremities were reviewed at our institution between 1939 and 2012. Follow-up data included clinical and radiographical information focusing on complications, local recurrence, metastasis, and overall survival after the treatment. The mean follow-up was 16 years (range 2-42 years). RESULTS: The most common location was the tibia (n = 31). Patients commonly presented with pain and swelling. The mean age was 24 years (7-79 years). Thirty-seven patients were treated with limb salvage. The 39% of patients required a reoperation. The 10-year disease specific- and recurrence free survival was 92% and 72%, with three patients having a recurrence over 15 years postoperative. Older (> 20 years) patients and males were at increased risk of local recurrence (P < 0.05). CONCLUSION: Treatment of adamantinoma of the long bone consists of limb-salvage surgery. Male patients should be cautioned on their increased risk of disease recurrence, and advocate for continued surveillance of patients even greater than 15-years postoperatively due to late tumor recurrence.

Imaging characteristics of intravascular papillary endothelial hyperplasia.

PURPOSE: Intravascular papillary endothelial hyperplasia (IPEH) is a soft tissue, tumor-like, benign, reactive, vascular proliferation that, although not rare, is uncommonly imaged. We report the imaging findings of intravascular papillary endothelial hyperplasia in 13 patients, highlighting characteristic imaging features. MATERIALS AND METHODS: We retrospectively reviewed 13 patients with IPEH who had corresponding MR and/or ultrasound imaging. MR imaging studies were evaluated for lesion location, shape, size, signal intensity, signal heterogeneity, and enhancement. Ultrasound studies were assessed for lesion shape, size, echogenicity, heterogeneity, and vascularity. Demographic data, including patient age, gender, and clinical history were also reviewed. RESULTS: Most patients (11 of 13) presented with an enlarging mass. The age range was 10-72 years (mean 46) with ten females and three males. Eleven of the 13 lesions were primary IPEH without an associated preexisting vascular lesion. Ten of 13 lesions were in the superficial soft tissues, all of which were primary IPEH. Two of the three lesions in the deep tissues were secondary IPEH, arising within a preexisting vascular lesion. Lesions were small (mean 1.4 cm) and had a rounded shape. All of the primary lesions demonstrated high T2 signal peripherally and variable T2 signal centrally, with most demonstrating superficial location (91 %), peripheral enhancement (89 %) and associated dominant vessel (73 %). The five lesions evaluated by ultrasound were all hypoechoic with either scattered or peripheral vascularity on Doppler. CONCLUSIONS: Primary papillary endothelial hyperplasia is commonly seen in the superficial soft tissues when captured on imaging and has a characteristic imaging appearance.

Imaging features of synovial chondromatosis of the spine: a review of 28 cases.

OBJECTIVE: To describe the radiographic, CT, and MRI appearance of synovial chondromatosis of the spine. MATERIALS AND METHODS: Radiology and pathology databases were searched for cases of spinal synovial chondromatosis from 1984 through 2013, yielding 29 patients (16 males, 13 females). The average age was 45 years. Twenty-eight patients had imaging studies available for review including seven radiographs, two myelograms, 13 CT, and 23 MRI exams. RESULTS: Cases were located in the cervical spine (16), thoracic spine (6), lumbar spine (6), and sacrum (1). Twenty-two cases (79%) had an epidural component. Eighteen (64%) had a neural foraminal component. Sixteen (57%) had a paraspinal component. The mass abutted a facet joint in 96% of cases. Nearly all (96%) showed a normal facet joint without internal erosive changes. Most (79%) showed evidence of chronic extrinsic bony erosion, usually involving the surface of the facet. Only 44% had calcifications as a dominant finding. Most patients (88%) had evidence of neural compression. On T1-weighted MRI, 80% showed intermediate or a combination of intermediate and dark signal. On T2-weighted images, 89% showed heterogeneous signal with discrete areas of dark signal. The majority (83%) showed a peripheral pattern of enhancement, usually peripheral nodular. CONCLUSIONS: Synovial chondromatosis should be considered in the differential diagnosis when evaluating an epidural and/or paraspinal mass near a facet joint, especially when there is evidence of chronic extrinsic bone erosion, dark signal or nodules on T1 and/or T2, and nonenhancing fluid or myxoid signal centrally with thin or nodular peripheral enhancement.

Chondrosarcoma arising within a radiation-induced osteochondroma several years following childhood total body irradiation: case report.

Malignant degeneration arising in radiation-induced osteochondromas is extremely rare. We report a case of a 34-year-old man with a chondrosarcoma arising from an osteochondroma of the left posterior eighth rib that developed following total body irradiation received as part of the conditioning regimen prior to bone marrow transplantation at age 8. To our knowledge, this is only the fourth reported case of a chondrosarcoma arising within a radiation-induced osteochondroma and the first case occurring following childhood total body irradiation.

Evaluation of Long-Term Follow-Up in Ecchordosis Physaliphora versus Chordoma.

OBJECTIVE: Ecchordosis physaliphora (EP) is a non-neoplastic notochord remnant with limited literature. We present a review on surgically resected clival EP to evaluate if available follow-up is adequate to distinguish EP from chordomas. METHODS: A systematic literature review was completed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Case reports or series of adults with histopathologic and radiographic findings of surgically resected EP were included. Articles including pediatric patients, systematic reviews, chordomas, and without microscopic or radiographic confirmation, or the surgical approach, were excluded. Corresponding authors were contacted twice to further evaluate outcomes. RESULTS: Eighteen articles were included (n = 25 patients; mean age 47.5 years ± 12.6 [standard deviation] months). All patients had symptomatic, surgically resected EP, with cerebrospinal fluid leak or rhinorrhea the most common symptom (48%). All but 3 had gross total resection, with endoscopic endonasal transsphenoidal transclival the most common approach (80%). All but 3 reported immunohistochemistry findings, with physaliphorous cells the most common. All but 5 patients had definitive follow-up (80%), with average of 19.5 ± 17.2 months. One corresponding author reported longer-term follow-up for 1 patient (57 months). No recurrence or malignant transformation was reported. Mean time to clival chordoma recurrence (53.9 ± 26.8 months) was also evaluated in a review of 8 studies. CONCLUSIONS: Mean follow-up for resected EP was almost 3 times shorter than mean time to recurrence of chordomas. Available literature is likely inadequate to confirm the suspected benign nature of EP especially in reference to chordoma, precluding treatment and follow-up recommendations.

Interobserver reliability in the histopathological diagnosis of cartilaginous tumors in patients with multiple osteochondromas.

The distinction between benign and malignant cartilaginous tumors located peripherally in the bone may be a challenging task in surgical pathology. The aim of this study was to investigate interobserver reliability in histological diagnosis of cartilaginous tumors in the setting of multiple osteochondromas and to evaluate possible histological parameters that could differentiate among osteochondroma, low- and high-grade secondary peripheral chondrosarcoma. Interobserver reliability was assessed by 12 specialized bone-tumor pathologists in a set of 38 cases. Substantial agreement on diagnosis among all the reviewers was observed (intraclass correlation coefficient=0.78). Our study confirmed that mitotic figures and nuclear pleomorphism are hallmarks of high-grade secondary peripheral chondrosarcoma. However, despite the substantial agreement, we demonstrated that histology alone cannot distinguish osteochondroma from low-grade secondary peripheral chondrosarcoma in the setting of multiple osteochondromas, as nodularity, the presence of binucleated cells, irregular calcification, cystic/mucoid changes and necrosis were not helpful to indicate malignant transformation of an osteochondroma. On the other hand, among the concordant cases, the cartilage cap in osteochondroma was significantly less thicker than in low- and high-grade secondary peripheral chondrosarcoma. Therefore, our study showed that a multidisciplinary approach integrating clinical and radiographical features and the size of the cartilaginous cap in combination with a histological assessment are crucial to the diagnosis of cartilaginous tumors.

Posttraumatic Glomus Tumor of the Digital Nerve with Atypical Presentation: A Case Report.

CASE: A 53-year-old man sustained an injury to his left index finger and underwent presumably traumatic neuroma excision from the radial digital nerve 2 years ago. He presented with a painful mass distal to the prior site of neuroma excision with distinctly different symptoms from those that led to his index surgery. Thus, he underwent excisional biopsy of the mass which was adherent to his radial digital nerve consistent with a benign glomus tumor on histologic examination. CONCLUSION: Digital nerve glomus tumors are rare. In most of the cases, some portion of the digital nerve requires excision but decreased pain can be expected.

MRI enhancement patterns in 28 cases of clival chordomas.

Clival chordomas are classically thought of as locally aggressive tumors of the skull base and differentiate themselves from their benign counterparts by demonstrating moderate to marked contrast enhancement, reported as 95-100% in prior studies. The purpose of this review was to evaluate the imaging characteristics of lesions from a single institution classified as clival chordomas with an emphasis of highlighting lesions that do not follow the prevalent current description for chordoma. We searched our institutional databases for all patients with pathologically proven clival chordomas from 1997 to 2017 who had pre-operative imaging available. The images were evaluated for degree of contrast enhancement, MRI signal characteristics, osseous involvement, location, aggressiveness of appearance, and presence of calcifications. 28 cases were identified that had preoperative imaging available for review. Over half of the patients demonstrated either no/minimal (11/28, 39%) or mild enhancement (7/28, 25%). The remaining cases demonstrated moderate (4/28, 14%) and marked enhancement (6/28, 21%). The 4 lesions measuring less than 20 mm all had mild to minimal/no enhancement and lacked aggressive features on CT. Our experience finds that over half (64%) of clival chordomas will demonstrate mild or no enhancement at all. These findings suggest that the lack of MRI contrast enhancement should not be synonymous with a benign clival mass.

Surgical approach and oncologic outcomes following multidisciplinary management of retrorectal sarcomas.

BACKGROUND: Retrorectal sarcomas are rare, and limited data are available on oncologic outcomes following surgery. Our aim was to evaluate outcomes in this patient population at our institution. MATERIALS AND METHODS: All patients who underwent surgical resection of a malignant retrorectal/presacral sarcoma between 1985 and 2005 were identified. Data analyzed included demographics, histopathologic diagnosis, surgical morbidity and mortality, use of adjuvant therapy, local and distant recurrence, and survival. RESULTS: A total of 37 patients were identified (20 males) with a median age of 49 years (range, 22-81 years). The most common histopathologic diagnosis was malignant peripheral nerve sheath tumor (n = 8). Also, 22 tumors were high grade and 15 were low grade. Surgical margin status was R0 in 31 patients and R1 in 6. Adjuvant therapy was given to 26 patients. Postoperative morbidity and mortality was 57% and 3%, respectively. Median length of follow-up in 16 patients alive at last contact was 4.7 years. The 5-year survival free of local (LDFS), distant (DDFS), and local or distant recurrence (DFS) was 51, 58, and 39%, respectively. Patient survival at 2, 5, and 10 years was 75, 55, and 47%, respectively. Disease-free survival was not significantly associated with gender (P = .16), primary vs secondary (P = .94), R0 vs R1 resection (P = .26), low vs high tumor grade (P = .17), or the use of surgery with or without adjuvant therapy (P = .33). CONCLUSIONS: Retrorectal sarcomas are often high grade and locally advanced. Most tumors are resectable with free margins, and long-term survival may be possible in up to one-half of patients following an aggressive surgical approach.

Benign bone tumors--recent developments.

Benign bone tumors frequently pose a diagnostic challenge for general surgical pathologists. Accurate pathologic diagnosis requires careful clinical and radiological correlation. The most significant recent advances in some benign bone tumors have occurred at the molecular and cytogenetic level. The detection of clonal chromosomal aberrations, various specific molecular genetic events, and the description of the bone cell signaling pathways in the field of osteoimmunology have provided a better understanding of the pathophysiology of certain tumors and an important aid in the diagnostic workup and differential diagnosis of some bone lesions demonstrating overlapping clinical and pathologic features. Future directions include prognostic and therapeutic applications of these findings. Newer less invasive therapeutic techniques and medical management have been developed for the treatment of certain benign bone tumors.

Giant cell tumor of bone: risk factors for recurrence.

BACKGROUND: Many surgeons treat giant cell tumor of bone (GCT) with intralesional curettage. Wide resection is reserved for extensive bone destruction where joint preservation is impossible or when expendable sites (eg, fibular head) are affected. Adjuvants such as polymethylmethacrylate and phenol have been recommended to reduce the risk of local recurrence after intralesional surgery. However, the best treatment of these tumors and risk factors for recurrence remain controversial. QUESTIONS/PURPOSES: We evaluated the recurrence-free survival after surgical treatment of GCT to determine the influence of the surgical approach, adjuvant treatment, local tumor presentation, and demographic factors on the risk of recurrence. METHODS: We retrospectively reviewed 118 patients treated for benign GCT of bone between 1985 and 2005. Recurrence rates, risk factors for recurrence and the development of pulmonary metastases were determined. The minimum followup was 36 months (mean, 108.4 ± 43.7; range, 36-233 months). RESULTS: Wide resection had a lower recurrence rate than intralesional surgery (5% versus 25%). Application of polymethylmethacrylate decreased the risk of local recurrence after intralesional surgery compared with bone grafting; phenol application alone had no effect on the risk of recurrence. Pulmonary metastases occurred in 4%; multidisciplinary treatment including wedge resection, chemotherapy, and radiotherapy achieved disease-free survival or stable disease in all of these patients. CONCLUSION: We recommend intralesional surgery with polymethylmethacrylate for the majority of primary GCTs. Because pulmonary metastases are rare and aggressive treatment of pulmonary metastases is usually successful, we believe the potential for metastases should not by itself create an indication for wide resection of primary tumors. LEVEL OF EVIDENCE: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Recurrent giant cell tumor of long bones: analysis of surgical management.

BACKGROUND: Treatment of giant cell tumor of bone (GCT) often is complicated by local recurrence. Intralesional curettage is the standard of care for primary GCTs. However, there is controversy whether intralesional curettage should be preferred over wide resection in recurrent GCTs. QUESTIONS/PURPOSES: We investigated the rerecurrence-free survival after surgical treatment of recurrent GCTs to determine the influence of the surgical approach, adjuvant treatment, local tumor presentation, and demographic factors on the risk of further recurrence. PATIENTS AND METHODS: We retrospectively reviewed the medical records of 46 patients with recurrent GCTs of long bones treated with wide resection or intralesional curettage and compared these cohorts. Recurrence rates, risk factors for recurrence, and the development of pulmonary metastases were determined. The minimum followup was 37 months (mean, 134 months; range, 37-337 months). RESULTS: The rate of rerecurrence after wide resection was 6%. Intralesional curettage showed an overall rerecurrence rate of 32%. Implantation of polymethylmethacrylate (PMMA) instead of bone grafting was associated with a lower risk of subsequent recurrence in intralesional procedures (14% versus 50%). Extracompartmental disease did not increase the risk of rerecurrence. Pulmonary metastases occurred in seven patients and appeared independent of the surgical treatment modality chosen. CONCLUSIONS: Intralesional curettage with methylmethacrylate for recurrent GCT provided equivalent tumor control compared with resection in this retrospective study. If joint salvage is possible, we advocate this treatment over resection in recurrent GCTs to preserve the native joint articulation. LEVEL OF EVIDENCE: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Imaging features of glomus tumors.

OBJECTIVE: To describe the imaging findings with pathologic correlation and clinical presentation of glomus tumors. MATERIALS AND METHODS: We retrospectively searched the surgical pathology database from January 1, 1997, to April 30, 2010, for cases of pathologically proven glomus tumor. Patients who had imaging results available for review were included in the study. RESULTS: Glomus tumors presented with a prolonged history of focal and often debilitating pain, with a mean duration of symptoms of 7.2 years. Mean tumor size was 13 mm. The upper extremity was involved in 12/25 (48%) of the tumors, the lower extremity in 12/25 (48%), and one case (4%) was within the trachea. Lesions appeared well circumscribed on ultrasonography, with marked vascularity on color Doppler evaluation. Magnetic resonance imaging (MRI) with a marker placed in the region of point tenderness was the best method for identifying small glomus tumors. These tumors had a high T2 signal and uniform enhancement after gadolinium administration. CONCLUSIONS: The diagnosis of glomus tumor is suggested by imaging features of a small circumscribed mass at the site of point tenderness that show marked vascularity on Doppler evaluation or diffuse contrast medium enhancement on MRI, or both. Early tumor recognition allows surgical resection that completely resolves the crippling, chronic pain of these lesions.

Fibrous Dysplasia at Unusual Anatomic Sites: A Series of 86 Cases With Emphasis on Histologic Patterns.

Aims. Fibrous dysplasia (FD) is a benign fibro-osseous neoplasm that most commonly arises in the ribs, femur, and craniofacial bones. We analyzed features of FD arising in the spine/short tubular/small bones of the hands/feet (STSBHF), specifically assessing for pattern of bone formation (conventional, complex/anastomosing, psammomatoid/cementum like), myxoid change, and presence of osteoclast-type giant cells. Materials and methods. A total of 1958 cases of FD were reviewed, of which 131 arose in the spine/STSBHF representing 2.5% of institutional and 10% of consultation cases, respectively. Eighty-six cases had material available for review. Anatomic sites included vertebrae (n = 58, 67%), short tubular bones (n = 20, 23%), and small bones of the hands/feet (n = 8, 9%). The most common morphologic pattern of bone identified was conventional (n = 77, 90%), followed by complex/anastomosing (n = 22, 26%) and psammomatoid/cementum like (n = 22, 26%). Eighteen cases (21%) had matrix-poor areas. Hypercellular areas were identified in 6 cases, 2 cases of which showed matrix-poor areas. Osteoclast-type giant cells were noted in 9 cases and myxoid change was present in 3 cases. Radiologic imaging studies available for 41 cases nearly all demonstrated features typical of FD, but the diagnosis was not predicted due to the unexpected location. Conclusions. FD arising in the spine/STSBHF is rare and frequently results in expert consultation. A significant number of cases exhibited less commonly recognized patterns of bone formation, and stromal changes including osteoclast-type giant cells, and matrix poor areas. Furthermore, imaging features in the STSBHF are often less specific. Awareness of the morphologic spectrum at these locations coupled with radiologic correlation should aid in accurate classification.