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A giant radiopaque mass in the masticatory space
Vol. 115 No. 5 May 2013
CLINICOPATHOLOGIC CONFERENCE
A giant radiopaque mass in the masticatory space Young-Ah Cho, DDS,a Hye-Jung Yoon, DDS, PhD,b Seong-Doo Hong, DDS, PhD,c Jae-Il Lee, DDS, PhD,d and Sam-Pyo Hong, DDS, PhD,d Seoul, Korea SEOUL NATIONAL UNIVERSITY
A 2-year-old boy presented with a giant mass in the masticatory space. The mass exhibited a lobulating ossification, with no attachment to the adjacent normal bone. An enucleation was performed under the tentative diagnosis of extraarticular synovial chondromatosis, benign ossifying neoplasm, non-neoplastic heterotopic ossification, or low-grade malignancy. Upon microscopic examination, the excised mass was composed of multiple osteocartilaginous areas. We hereby present detailed clinicopathological findings. (Oral Surg Oral Med Oral Pathol Oral Radiol 2013;115:566-570)
CLINICAL PRESENTATION A 2-year-old boy presented with a mass in his left masticatory area that limited mouth opening and resulted in respiratory difficulty during sleep. This mass was first noticed in the oral cavity by a pediatrician, who referred the patient to the Oral and Maxillofacial Surgery Clinic at the Seoul National University Dental Hospital, Seoul, Korea. Computed tomography revealed a 4.5 ⫻ 4.0 ⫻ 3.5-cm, well-demarcated mass in the left masticatory space (Figure 1). The entire lesion was multilobulated and was composed of heterogeneously calcified bodies. The left pterygoid process was surrounded by the mass, without any connection. The lesion was pressing on the parapharyngeal space and was separated from it by a thin fat layer. The medial surface of the left mandible was also deformed by the mass. No morphologic deformity or pathologic condition of the temporomandibular joint was identified. The medical history of the patient was noncontributory. DIFFERENTIAL DIAGNOSIS The presentation of slow-growing behavior with no infiltration of the mass into the adjacent structures indicated a benign process. Based on the lobulating ossification, our clinical differential diagnosis included synovial chondromatosis (SC), benign ossifying neoa
Lecturer, Department of Pathology, School of Dentistry, Seoul National University, Seoul, Korea. b Assistant Professor, Department of Pathology, School of Dentistry, Seoul National University, Seoul, Korea. c Associate Professor, Department of Pathology, School of Dentistry, Seoul National University, Seoul, Korea. d Professor, Department of Pathology, School of Dentistry, Seoul National University, Seoul , Korea. Received for publication Apr 21, 2011; returned for revision Dec 14, 2011; accepted for publication Jan 2, 2012. © 2013 Elsevier Inc. All rights reserved. 2212-4403/$ - see front matter doi:10.1016/j.oooo.2012.01.008
566
plasm, and non-neoplastic heterotopic ossification. In addition, an infrequent case of low-grade chondrosarcoma with demarcated margins was considered. Because the masticatory space is in proximity to the temporomandibular joint, extra-articular SC was the most likely differential diagnosis. SC is characterized by the metaplastic development of multiple cartilaginous nodules within the synovial membrane.1-7 Even though most cases occur in the joints, SC can arise from tendon sheaths and bursae that do not communicate with a joint space, while still originating from synovial cells.5-7 This type of SC, known as extra-articular SC, is most common in the hands or feet.6,8 There is no predilection for sex or age,5 but prepubescent patients with extra-articular SC are evidently rare, with only a handful of cases in the Englishlanguage literature. Patients may remain asymptomatic, but usually present with tenderness, pain, swelling, and limitation of motion.5,6,8 The cartilaginous nodules are often calcified and radiographically appear as multiple articular or periarticular nodules with stippled or arc-/ ringlike radiopacities. Some benign ossifying tumors, such as soft tissue chondromas, can develop in the soft tissues without bony continuity. Even though a soft tissue chondroma is obviously a rare tumor, one case has been reported in the masticatory space.9 Usually, soft tissue chondromas occur in the hands and feet.9,10 They affect middle-aged and older adults and show a slight preference for men.10 The lesion presents radiographically as a well-circumscribed solitary mass with lobulation.6,10 The common pattern of calcification is curvilinear radiopacities that outline the inner soft tissue lobules.11 One case of soft tissue osteoma has also been reported in the masticatory space.12 Soft tissue osteomas are most frequently observed in the tongue and skin,12,13 and such lesions can also be referred to as osseous choristomas. Although these lesions are clinically described as a sessile or pedunculated nodule,14 soft tissue osteomas arising in
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CLINICOPATHOLOGIC CONFERENCE Cho et al. 567
Fig. 1. Computed tomography scan, bone window. A, Axial view shows that a lobulated spherical mass surrounds the left pterygoid process. Note that the mandible is deformed by the mass (arrowheads). B, Coronal view of the lesion. There is no change in the temporomandibular joint space or the surface of the condylar process.
deep soft tissue, which are very rare, are seen as a lobulated homogeneous radiopaque mass with welldefined margins.12,13 Ossifying fibromyxoid tumors of soft tissue are rare tumors of uncertain differentiation that most commonly involve the lower extremities. These tumors seldom occur in people younger than 20 years, and a male predilection has been noted. Radiographs reveal a well-circumscribed mass with an incomplete ring of peripheral radiopacities.15,16 Myositis ossificans is a synonym for heterotopic ossification, a reactive bone-forming condition of the soft tissues.4,17 The most common locations are the thigh and upper arm.18 Although adolescents and young adults are most often affected,4,18 a few cases have been reported in children.18 Patients complain of a rapidly enlarging painful swelling. Radiographically, the lesion demonstrates ill-defined margins in the early stage, but the lesion begins to present with a well-marginated soft tissue mass after 6 to 8 weeks, as peripheral bone formation progresses.4,18 It has been reported that some heterotopic ossifications occur within the pterygoid muscle as a consequence of local anesthetic injections or pericoronitis of the mandibular third molars.17 Chondrosarcomas are usually osteolytic and infiltrative, but 5% or fewer of chondrosarcomas radiographically demonstrate sharp margins.4 Also, mesenchymal chondrosarcoma, one of the rare chondrosarcoma subtypes, sometimes occurs in the soft tissue without causing the cortical changes of the adjacent bone.6,19 These extraskeletal mesenchymal chondrosarcomas usually show stippled calcifications within a mass in radiographs.19 Synovial chondrosarcoma arising from longstanding primary SC can also present as a soft tissue mass, and their clinical and radiologic features are often
indistinguishable from those of SC6,20; however, SC has never been reported in pediatric patients.20
DIAGNOSIS AND MANAGEMENT An enucleation was performed under general anesthesia. In view of the large size of the lesion, the medial half was removed via an intraoral approach (Figure 2, A), and the distal half was excised through an extraoral submandibular incision (Figure 2, B). The mass appeared to be well encapsulated and easily detached from the adjacent pterygoid plate and mandibular body. On microscopic examination, the excised mass was found to be developing in a lobulated pattern, which was consistent with the radiographs. One end of each lobule was composed of hyaline cartilage that had undergone ossification toward the other end. Some large lobules, 1.0 to 1.5 cm in diameter, were separated by fibrous septa, and smaller lobules tended to be merged with one another (Figure 3). In the cartilaginous portion, there were no characteristics of chondromatous proliferation, including clustering of chondrocytes, mild nuclear enlargement, hyperchromatism, or double nuclei in a lacuna. All the chondrocytes became hypertrophic and died during matrix calcification (Figure 4). The bony trabeculae underwent remodeling into lamellar bone as it grew farther from the cartilage. Osteoclasts were observed to have formed cavities between the trabeculae, but the bone marrow was not being formed (Figure 5). No mitotic figures were seen. Consequently, the final diagnosis of an extraskeletal osteochondroma was established. The preoperative symptoms improved after the operation. The patient was followed for 2 years with no signs of recurrence.
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Fig. 2. Surgical approach for mass removal. A, An intraoral incision was performed to split the mass in half and remove the medial half, which was pushing the parapharyngeal space. B, The distal half of the tumor adjacent to the mandibular body was removed through a submandibular approach.
Fig. 3. Bony trabeculae of small lobules (asterisks) are being formed from hyaline cartilage and merged with the adjacent small lobules. Part of a larger lobule with a cartilage cap is seen at the bottom left of the figure. Dense fibrous tissue (arrows) exists between the larger lobules (hematoxylin-eosin [HE], scale bar ⫽ 1 mm).
DISCUSSION Extraskeletal osteochondroma is a neoplasm that exhibits the histologic features of osteochondromas without connection to normal bone.1-3,21,22 Although conventional osteochondromas represent one-third of all bone tumors,2,4,23 extraskeletal osteochondromas are very uncommon, and lesions far from the joints are even more rare.1-3 Only one case has been reported in the maxillofacial region.21 Even though the clinical behavior of extraskeletal osteochondroma is poorly characterized, it seems that extraskeletal osteochondromas are more common in
Fig. 4. Simultaneous with the death of hypertrophic chondrocytes, the surrounding cartilage matrix is calcified. Fibrovascular tissue invades the space left by the dead chondrocytes (HE, original magnification ⫻100).
people older than 30 years than in younger adults or children.22,24,25 Therefore, we can speculate that some extraskeletal osteochondromas arise and continue to grow after skeletal maturity, in contrast to traditional osteochondromas, which stop growing when a person reaches full height.5,22,24,25 The symptoms of extraskeletal osteochondromas are similar to those of the conventional type: the mass is usually slow growing and painless but sometimes can cause pain or limit motion.2,25 Osteochondromas occur as a result of the normal endochondral ossification of the ectopic cartilage, such as a misplaced epiphyseal plate on the surface of the metaphysis.4,23 Rarely, the ectopic cartilaginous rudi-
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Fig. 5. On the opposite side of the cartilage, bony remodeling continues without apparent bone marrow tissue (HE, original magnification ⫻100).
ments seem to develop in the soft tissue, and the formation of extraskeletal osteochondroma results from typical endochondral ossification of those cartilage tissues1,2; however, the origin of the cartilage in extraskeletal osteochondromas is unclear. It has been thought that chondrocytes might be derived from the adjacent joint, differentiated from pluripotent stem cells, or formed by metaplasia.1,2,25,26 Multiple osteocartilaginous areas may be observed in an extraskeletal osteochondroma.22 The present lesion developed in a lobulated pattern, with the cartilage of each lobule being ossified in different directions. Therefore, there must have been multiple cartilaginous rudiments in the masticatory space, which seemed to commence ossification independently and grow in arbitrary directions, in contrast to the conventional osteochondromas that have a single cartilage cap and usually grow at a right angle to the bony surface.23 Also, these multiple ossification centers are reminiscent of rare developmental disorders of childhood, such as dysplasia epiphysealis hemimelica (DEH). Although they also show typical endochondral ossification, DEHs arise from the epiphysis of the long bones and involve one side of the affected joint (hemimelic). Histologically, DEH is distinguished by the evident bands of cartilage surrounding bony nodules, similar to a secondary center of ossification in long bones.27 The present lesion demonstrated active endochondral ossification, but the chondrocytes were not atypical at all and finally became apoptotic with the formation of cavities for bone marrow tissue. When endochondral ossification is inactive, extraskeletal osteochondromas are mainly composed of bony trabeculae, and the remaining noncalcified cartilage appears similar to the articular cartilage of long bone or the cartilage cap
CLINICOPATHOLOGIC CONFERENCE Cho et al. 569
of conventional osteochondromas after the growth phase.2,26 Although it has been reported that the cartilaginous portion of extraskeletal osteochondromas may contain chondrocytes with enlarged nuclei and/or binucleated cells,2,22 each of these cartilages would undergo typical endochondral ossification, unlike in some tumorlike conditions that show atypical chondrocytes, such as extra-articular SC and bizarre parosteal osteochondromatous proliferation.4-6,28 On the other hand, the cytologic atypia may suggest chondrosarcoma arising secondarily in the cartilage of an osteochondroma. A careful correlation between the histopathological and clinical/radiographic findings can help rule out malignancy.22 Extraskeletal osteochondromas need to be removed to relieve functional and esthetic impairments.29 Marginal excision accompanied by careful removal of the entire cartilage, which is important to avoid recurrence, is the preferred treatment.1,4,22 Consequently, the diagnosis of extraskeletal osteochondroma should be considered when a well-circumscribed, radiopaque mass is seen in the soft tissues, including the masticatory muscle. REFERENCES 1. Singh R, Sharma AK, Magu NK, Kaur KP, Sen R, Magu S. Extraskeletal osteochondroma in the nape of the neck: a case report. J Orthop Surg (Hong Kong) 2006;14:192-5. 2. Spencer RJ, Blitz NM. Giant extraskeletal osteochondroma of the plantar midfoot arch. J Foot Ankle Surg 2008;47:362-7. 3. Maheshwari AV, Jain AK, Dhammi IK. Extraskeletal paraarticular osteochondroma of the knee—a case report and tumor overview. Knee 2006;13:411-4. 4. Unni KK, Inwards CY, Bridge JA, Kindblom LG, Wold LE. Tumors of the bones and joints, AFIP, Atlas of tumor pathology, series 4. Washington DC: American registry of pathology; 2005. p. 37– 46. 5. Ko E, Mortimer E, Fraire AE. Extraarticular synovial chondromatosis: review of epidemiology, imaging studies, microscopy and pathogenesis, with a report of an additional case in a child. Int J Surg Pathol 2004;12:273-80. 6. Fetsch JF, Vinh TN, Remotti F, Walker EA, Murphey MD, Sweet DE. Tenosynovial (extraarticular) chondromatosis: an analysis of 37 cases of an underrecognized clinicopathologic entity with a strong predilection for the hands and feet and a high local recurrence rate. Am J Surg Pathol 2003;27:1260-8. 7. Milgram JW. Synovial osteochondromatosis: a histopathological study of thirty cases. J Bone Joint Surg Am 1977;59:792-801. 8. Sim FH, Dahlin DC, Ivins JC. Extra-articular synovial chondromatosis. J Bone Joint Surg Am 1977;59:492-5. 9. De Riu G, Meloni SM, Gobbi R, Contini M, Tullio A. Soft-tissue chondroma of the masticatory space. Int J Oral Maxillofac Surg 2007;36:174-6. 10. Hondar Wu HT, Chen W, Lee O, Chang CY. Imaging and pathological correlation of soft-tissue chondroma: a serial fivecase study and literature review. Clin Imaging 2006;30:32-6. 11. Han JY, Han HS, Kim YB, Kim JM, Chu YC. Extraskeletal chondroma of the fallopian tube. J Korean Med Sci 2002; 17:276-8.
CLINICOPATHOLOGIC CONFERENCE 570 Cho et al. 12. Li G, Wu YT, Chen Y, Li TJ, Gao Y, Zhang J, et al. Soft-tissue osteoma in the pterygomandibular space: report of a rare case. Dentomaxillofac Radiol 2009;38:59-62. 13. Kasper HU, Adermahr J, Dienes HP. Soft tissue osteoma: tumour entity or reactive lesion? Paraarticular soft tissue osteoma of the hip. Histopathology 2004;44:91-3. 14. Chou LS, Hansen LS, Daniels TE. Choristomas of the oral cavity: a review. Oral Surg Oral Med Oral Pathol 1991;72: 584-93. 15. Weiss SW, Goldblum JR. Enzinger and Weiss’s soft tissue tumors. 5th ed. St. Louis: Mosby: 2008; p. 1093–101. 16. Miettinen M, Finnell V, Fetsch JF. Ossifying fibromyxoid tumor of soft parts—a clinicopathologic and immunohistochemical study of 104 cases with long-term follow-up and a critical review of the literature. Am J Surg Pathol 2008;32:996-1005. 17. Aoki T, Naito H, Ota Y, Shiiki K. Myositis ossificans traumatica of the masticatory muscles: review of the literature and report of a case. J Oral Maxillofac Surg 2002;60:1083-8. 18. Gindele A, Schwamborn D, Tsironis K, Benz-Bohm G. Myositis ossificans traumatica in young children: report of three cases and review of the literature. Pediatr Radiol 2000;30:451-9. 19. Nakashima Y, Unni KK, Shives TC, Swee RG, Dahlin DC. Mesenchymal chondrosarcoma of bone and soft tissue. A review of 111 cases. Cancer 1986;57:2444-53. 20. Schlachter TR, Wu Q, Matlyuk-Urman Z. AIRP best cases in radiologic-pathologic correlation: synovial chondrosarcoma. RadioGraphics 2011;31:1883-8. 21. Sakai H, Minemura T, Ito N, Miyazawa H, Kurashina K. Isolated osteochondroma near the mandibular angle. Int J Oral Maxillofac Surg 2007;36:274-5. 22. Reith JD, Bauer TW, Joyce MJ. Paraarticular osteochondroma of the knee: report of 2 cases and review of the literature. Clin Orthop Relat Res 1997;334:225-32.
OOOO May 2013 23. Chin KR, Kharrazi FD, Miller BS, Mankin HJ, Gebhardt MC. Osteochondromas of the distal aspect of the tibia or fibula. Natural history and treatment. J Bone Joint Surg Am 2000;82:1269-78. 24. Oliva F, Marconi A, Fratoni S, Maffulli N. Extra-osseous osteochondroma-like soft tissue mass of the patello-femoral space. BMC Musculoskelet Disord 2006;7:57. 25. Lim SC, Kim YS, Kim YS, Moon YR. Extraskeletal osteochondroma of the buttock. J Korean Med Sci 2003;18:127-30. 26. Liu ZJ, Zhao Q, Zhang LJ. Extraskeletal osteochondroma near the hip: a pediatric case. J Pediatr Orthop B 2010;19:524-8. 27. Glick R, Khaldi L, Ptaszynski K, Steiner GC. Dysplasia epiphysealis hemimelica (Trevor disease): a rare developmental disorder of bone mimicking osteochondroma of long bones. Hum Pathol 2007;38:1265-72. 28. Shankly PE, Hill FJ, Sloan P, Thakker NS. Bizarre parosteal osteochondromatous proliferation in the anterior maxilla: report of a case. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;87:351-6. 29. Wu W, Hu X, Lei D. Giant osteochondroma derived from pterygoid process of sphenoid. Int J Oral Maxillofac Surg 2007; 36:959-62.
Reprint requests: Hye-Jung Yoon, DDS, PhD Department of Oral Pathology School of Dentistry Seoul National University 28 Yeongeon-dong Jongno-gu, Seoul 110 –749, Korea [email protected]
CLINICOPATHOLOGIC CONFERENCE
A giant radiopaque mass in the masticatory space Young-Ah Cho, DDS,a Hye-Jung Yoon, DDS, PhD,b Seong-Doo Hong, DDS, PhD,c Jae-Il Lee, DDS, PhD,d and Sam-Pyo Hong, DDS, PhD,d Seoul, Korea SEOUL NATIONAL UNIVERSITY
A 2-year-old boy presented with a giant mass in the masticatory space. The mass exhibited a lobulating ossification, with no attachment to the adjacent normal bone. An enucleation was performed under the tentative diagnosis of extraarticular synovial chondromatosis, benign ossifying neoplasm, non-neoplastic heterotopic ossification, or low-grade malignancy. Upon microscopic examination, the excised mass was composed of multiple osteocartilaginous areas. We hereby present detailed clinicopathological findings. (Oral Surg Oral Med Oral Pathol Oral Radiol 2013;115:566-570)
CLINICAL PRESENTATION A 2-year-old boy presented with a mass in his left masticatory area that limited mouth opening and resulted in respiratory difficulty during sleep. This mass was first noticed in the oral cavity by a pediatrician, who referred the patient to the Oral and Maxillofacial Surgery Clinic at the Seoul National University Dental Hospital, Seoul, Korea. Computed tomography revealed a 4.5 ⫻ 4.0 ⫻ 3.5-cm, well-demarcated mass in the left masticatory space (Figure 1). The entire lesion was multilobulated and was composed of heterogeneously calcified bodies. The left pterygoid process was surrounded by the mass, without any connection. The lesion was pressing on the parapharyngeal space and was separated from it by a thin fat layer. The medial surface of the left mandible was also deformed by the mass. No morphologic deformity or pathologic condition of the temporomandibular joint was identified. The medical history of the patient was noncontributory. DIFFERENTIAL DIAGNOSIS The presentation of slow-growing behavior with no infiltration of the mass into the adjacent structures indicated a benign process. Based on the lobulating ossification, our clinical differential diagnosis included synovial chondromatosis (SC), benign ossifying neoa
Lecturer, Department of Pathology, School of Dentistry, Seoul National University, Seoul, Korea. b Assistant Professor, Department of Pathology, School of Dentistry, Seoul National University, Seoul, Korea. c Associate Professor, Department of Pathology, School of Dentistry, Seoul National University, Seoul, Korea. d Professor, Department of Pathology, School of Dentistry, Seoul National University, Seoul , Korea. Received for publication Apr 21, 2011; returned for revision Dec 14, 2011; accepted for publication Jan 2, 2012. © 2013 Elsevier Inc. All rights reserved. 2212-4403/$ - see front matter doi:10.1016/j.oooo.2012.01.008
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plasm, and non-neoplastic heterotopic ossification. In addition, an infrequent case of low-grade chondrosarcoma with demarcated margins was considered. Because the masticatory space is in proximity to the temporomandibular joint, extra-articular SC was the most likely differential diagnosis. SC is characterized by the metaplastic development of multiple cartilaginous nodules within the synovial membrane.1-7 Even though most cases occur in the joints, SC can arise from tendon sheaths and bursae that do not communicate with a joint space, while still originating from synovial cells.5-7 This type of SC, known as extra-articular SC, is most common in the hands or feet.6,8 There is no predilection for sex or age,5 but prepubescent patients with extra-articular SC are evidently rare, with only a handful of cases in the Englishlanguage literature. Patients may remain asymptomatic, but usually present with tenderness, pain, swelling, and limitation of motion.5,6,8 The cartilaginous nodules are often calcified and radiographically appear as multiple articular or periarticular nodules with stippled or arc-/ ringlike radiopacities. Some benign ossifying tumors, such as soft tissue chondromas, can develop in the soft tissues without bony continuity. Even though a soft tissue chondroma is obviously a rare tumor, one case has been reported in the masticatory space.9 Usually, soft tissue chondromas occur in the hands and feet.9,10 They affect middle-aged and older adults and show a slight preference for men.10 The lesion presents radiographically as a well-circumscribed solitary mass with lobulation.6,10 The common pattern of calcification is curvilinear radiopacities that outline the inner soft tissue lobules.11 One case of soft tissue osteoma has also been reported in the masticatory space.12 Soft tissue osteomas are most frequently observed in the tongue and skin,12,13 and such lesions can also be referred to as osseous choristomas. Although these lesions are clinically described as a sessile or pedunculated nodule,14 soft tissue osteomas arising in
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CLINICOPATHOLOGIC CONFERENCE Cho et al. 567
Fig. 1. Computed tomography scan, bone window. A, Axial view shows that a lobulated spherical mass surrounds the left pterygoid process. Note that the mandible is deformed by the mass (arrowheads). B, Coronal view of the lesion. There is no change in the temporomandibular joint space or the surface of the condylar process.
deep soft tissue, which are very rare, are seen as a lobulated homogeneous radiopaque mass with welldefined margins.12,13 Ossifying fibromyxoid tumors of soft tissue are rare tumors of uncertain differentiation that most commonly involve the lower extremities. These tumors seldom occur in people younger than 20 years, and a male predilection has been noted. Radiographs reveal a well-circumscribed mass with an incomplete ring of peripheral radiopacities.15,16 Myositis ossificans is a synonym for heterotopic ossification, a reactive bone-forming condition of the soft tissues.4,17 The most common locations are the thigh and upper arm.18 Although adolescents and young adults are most often affected,4,18 a few cases have been reported in children.18 Patients complain of a rapidly enlarging painful swelling. Radiographically, the lesion demonstrates ill-defined margins in the early stage, but the lesion begins to present with a well-marginated soft tissue mass after 6 to 8 weeks, as peripheral bone formation progresses.4,18 It has been reported that some heterotopic ossifications occur within the pterygoid muscle as a consequence of local anesthetic injections or pericoronitis of the mandibular third molars.17 Chondrosarcomas are usually osteolytic and infiltrative, but 5% or fewer of chondrosarcomas radiographically demonstrate sharp margins.4 Also, mesenchymal chondrosarcoma, one of the rare chondrosarcoma subtypes, sometimes occurs in the soft tissue without causing the cortical changes of the adjacent bone.6,19 These extraskeletal mesenchymal chondrosarcomas usually show stippled calcifications within a mass in radiographs.19 Synovial chondrosarcoma arising from longstanding primary SC can also present as a soft tissue mass, and their clinical and radiologic features are often
indistinguishable from those of SC6,20; however, SC has never been reported in pediatric patients.20
DIAGNOSIS AND MANAGEMENT An enucleation was performed under general anesthesia. In view of the large size of the lesion, the medial half was removed via an intraoral approach (Figure 2, A), and the distal half was excised through an extraoral submandibular incision (Figure 2, B). The mass appeared to be well encapsulated and easily detached from the adjacent pterygoid plate and mandibular body. On microscopic examination, the excised mass was found to be developing in a lobulated pattern, which was consistent with the radiographs. One end of each lobule was composed of hyaline cartilage that had undergone ossification toward the other end. Some large lobules, 1.0 to 1.5 cm in diameter, were separated by fibrous septa, and smaller lobules tended to be merged with one another (Figure 3). In the cartilaginous portion, there were no characteristics of chondromatous proliferation, including clustering of chondrocytes, mild nuclear enlargement, hyperchromatism, or double nuclei in a lacuna. All the chondrocytes became hypertrophic and died during matrix calcification (Figure 4). The bony trabeculae underwent remodeling into lamellar bone as it grew farther from the cartilage. Osteoclasts were observed to have formed cavities between the trabeculae, but the bone marrow was not being formed (Figure 5). No mitotic figures were seen. Consequently, the final diagnosis of an extraskeletal osteochondroma was established. The preoperative symptoms improved after the operation. The patient was followed for 2 years with no signs of recurrence.
CLINICOPATHOLOGIC CONFERENCE 568 Cho et al.
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Fig. 2. Surgical approach for mass removal. A, An intraoral incision was performed to split the mass in half and remove the medial half, which was pushing the parapharyngeal space. B, The distal half of the tumor adjacent to the mandibular body was removed through a submandibular approach.
Fig. 3. Bony trabeculae of small lobules (asterisks) are being formed from hyaline cartilage and merged with the adjacent small lobules. Part of a larger lobule with a cartilage cap is seen at the bottom left of the figure. Dense fibrous tissue (arrows) exists between the larger lobules (hematoxylin-eosin [HE], scale bar ⫽ 1 mm).
DISCUSSION Extraskeletal osteochondroma is a neoplasm that exhibits the histologic features of osteochondromas without connection to normal bone.1-3,21,22 Although conventional osteochondromas represent one-third of all bone tumors,2,4,23 extraskeletal osteochondromas are very uncommon, and lesions far from the joints are even more rare.1-3 Only one case has been reported in the maxillofacial region.21 Even though the clinical behavior of extraskeletal osteochondroma is poorly characterized, it seems that extraskeletal osteochondromas are more common in
Fig. 4. Simultaneous with the death of hypertrophic chondrocytes, the surrounding cartilage matrix is calcified. Fibrovascular tissue invades the space left by the dead chondrocytes (HE, original magnification ⫻100).
people older than 30 years than in younger adults or children.22,24,25 Therefore, we can speculate that some extraskeletal osteochondromas arise and continue to grow after skeletal maturity, in contrast to traditional osteochondromas, which stop growing when a person reaches full height.5,22,24,25 The symptoms of extraskeletal osteochondromas are similar to those of the conventional type: the mass is usually slow growing and painless but sometimes can cause pain or limit motion.2,25 Osteochondromas occur as a result of the normal endochondral ossification of the ectopic cartilage, such as a misplaced epiphyseal plate on the surface of the metaphysis.4,23 Rarely, the ectopic cartilaginous rudi-
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Fig. 5. On the opposite side of the cartilage, bony remodeling continues without apparent bone marrow tissue (HE, original magnification ⫻100).
ments seem to develop in the soft tissue, and the formation of extraskeletal osteochondroma results from typical endochondral ossification of those cartilage tissues1,2; however, the origin of the cartilage in extraskeletal osteochondromas is unclear. It has been thought that chondrocytes might be derived from the adjacent joint, differentiated from pluripotent stem cells, or formed by metaplasia.1,2,25,26 Multiple osteocartilaginous areas may be observed in an extraskeletal osteochondroma.22 The present lesion developed in a lobulated pattern, with the cartilage of each lobule being ossified in different directions. Therefore, there must have been multiple cartilaginous rudiments in the masticatory space, which seemed to commence ossification independently and grow in arbitrary directions, in contrast to the conventional osteochondromas that have a single cartilage cap and usually grow at a right angle to the bony surface.23 Also, these multiple ossification centers are reminiscent of rare developmental disorders of childhood, such as dysplasia epiphysealis hemimelica (DEH). Although they also show typical endochondral ossification, DEHs arise from the epiphysis of the long bones and involve one side of the affected joint (hemimelic). Histologically, DEH is distinguished by the evident bands of cartilage surrounding bony nodules, similar to a secondary center of ossification in long bones.27 The present lesion demonstrated active endochondral ossification, but the chondrocytes were not atypical at all and finally became apoptotic with the formation of cavities for bone marrow tissue. When endochondral ossification is inactive, extraskeletal osteochondromas are mainly composed of bony trabeculae, and the remaining noncalcified cartilage appears similar to the articular cartilage of long bone or the cartilage cap
CLINICOPATHOLOGIC CONFERENCE Cho et al. 569
of conventional osteochondromas after the growth phase.2,26 Although it has been reported that the cartilaginous portion of extraskeletal osteochondromas may contain chondrocytes with enlarged nuclei and/or binucleated cells,2,22 each of these cartilages would undergo typical endochondral ossification, unlike in some tumorlike conditions that show atypical chondrocytes, such as extra-articular SC and bizarre parosteal osteochondromatous proliferation.4-6,28 On the other hand, the cytologic atypia may suggest chondrosarcoma arising secondarily in the cartilage of an osteochondroma. A careful correlation between the histopathological and clinical/radiographic findings can help rule out malignancy.22 Extraskeletal osteochondromas need to be removed to relieve functional and esthetic impairments.29 Marginal excision accompanied by careful removal of the entire cartilage, which is important to avoid recurrence, is the preferred treatment.1,4,22 Consequently, the diagnosis of extraskeletal osteochondroma should be considered when a well-circumscribed, radiopaque mass is seen in the soft tissues, including the masticatory muscle. REFERENCES 1. Singh R, Sharma AK, Magu NK, Kaur KP, Sen R, Magu S. Extraskeletal osteochondroma in the nape of the neck: a case report. J Orthop Surg (Hong Kong) 2006;14:192-5. 2. Spencer RJ, Blitz NM. Giant extraskeletal osteochondroma of the plantar midfoot arch. J Foot Ankle Surg 2008;47:362-7. 3. Maheshwari AV, Jain AK, Dhammi IK. Extraskeletal paraarticular osteochondroma of the knee—a case report and tumor overview. Knee 2006;13:411-4. 4. Unni KK, Inwards CY, Bridge JA, Kindblom LG, Wold LE. Tumors of the bones and joints, AFIP, Atlas of tumor pathology, series 4. Washington DC: American registry of pathology; 2005. p. 37– 46. 5. Ko E, Mortimer E, Fraire AE. Extraarticular synovial chondromatosis: review of epidemiology, imaging studies, microscopy and pathogenesis, with a report of an additional case in a child. Int J Surg Pathol 2004;12:273-80. 6. Fetsch JF, Vinh TN, Remotti F, Walker EA, Murphey MD, Sweet DE. Tenosynovial (extraarticular) chondromatosis: an analysis of 37 cases of an underrecognized clinicopathologic entity with a strong predilection for the hands and feet and a high local recurrence rate. Am J Surg Pathol 2003;27:1260-8. 7. Milgram JW. Synovial osteochondromatosis: a histopathological study of thirty cases. J Bone Joint Surg Am 1977;59:792-801. 8. Sim FH, Dahlin DC, Ivins JC. Extra-articular synovial chondromatosis. J Bone Joint Surg Am 1977;59:492-5. 9. De Riu G, Meloni SM, Gobbi R, Contini M, Tullio A. Soft-tissue chondroma of the masticatory space. Int J Oral Maxillofac Surg 2007;36:174-6. 10. Hondar Wu HT, Chen W, Lee O, Chang CY. Imaging and pathological correlation of soft-tissue chondroma: a serial fivecase study and literature review. Clin Imaging 2006;30:32-6. 11. Han JY, Han HS, Kim YB, Kim JM, Chu YC. Extraskeletal chondroma of the fallopian tube. J Korean Med Sci 2002; 17:276-8.
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Reprint requests: Hye-Jung Yoon, DDS, PhD Department of Oral Pathology School of Dentistry Seoul National University 28 Yeongeon-dong Jongno-gu, Seoul 110 –749, Korea [email protected]