Skeletal Radiology Skeletal Radiol (1987) 16:17(~174 Case report 415 Daryl Fanney, M.D., Jamshid Tehranzadeh, M.D., Robert M. Quencer, M.D., and Mehrdad Nadji, M.D. Departments of Radiology and Pathology, University of Miami School of Medicine, Miami, Florida, U S A Fig. 1. A technetium phosphate bone scan shows a localized area of increased activity in the mid line in the mid cervical region Fig. 2. A computed tomogram following a metrizamide myelogram obtained in the area of the lower cervical spine shows a multilobulated calcific and bony mass with a distinct cortex. Areas of attachment to the spinous process are present. No evidence of involvement of nerves or the spinal cord is apparent Address reprint requests to." Jamshid Tehranzadeh, M.D., Department of Radiology (R-130), University of Miami School of Medicine, P.O. Box 016960, Miami, FL 33101, USA 9 1987 International Skeletal Society D. Fanney et al. : Case report 415 171 Fig. 3. In this magnetic resonance study (mixed TI and T2 M R images, TR : 797 M5, TE : 40MS) sagittal views show an oval posterior mass with mixed signal intensity present from C3 through C7 Fig. 4. Another M R study (a heavily weighted T2 image T R = 2200 MS and TE:80 MS) in a sagittal view shows the same ovoid mass with an intense bright signal and lobulation CHnical information This 33-year-old man was admitted to the hospital with a firm, nontender mass in the posterior aspect of his neck. He first noted the mass two years before admission when he began to experience constant, non-throbbing pain exacerbated by lifting weights. The patient attributed the mass to muscle spasm. Six months prior to admission, however, the patient noticed that the mass was growing and began to experience paresthesias in the 4th and 5th digits of his right hand. No other complaint was elicited. His genera/health was good and the past history was unremarkable. On physical examination, a protruding, solid, nontender mass, approximately 7 x 4 cm, was palpated on the posterior portion of the neck with no evidence of discoloration of the skin or formation of fistula. A plain roentgenogram showed a large, amorphous, calcific and bony density in the soft tissues of the neck posteriorly. The technetium phosphate bone scan showed increased radionuclide activity in the same area (Fig. 1). A myelogram showed no evidence of neural involvement. Computed tomography, following the myelogram, showed a large, corticated, lobular density in the soft tissues of the neck posteriorly, with attachment to the spinous processes of C4, C5 and C6 (Fig. 2). A sagittal view of a magnetic resonance image at (TR--797 mS and TE: 40 mS) showed an oval, posterior mass with mixed signal intensity, extending from C3 to C7 (Fig. 3). A T2-weighted image (TR = 2200 mS and TE: 80 mS) in the sagittal view showed the same oval mass with a bright, intense signal with lobulation and septation (Fig. 4). An operation was performed. 172 D. Fanney et al. : Case report 415 Diagnosis: Osteochondroma of the cervical spine The differential diagnosis included chondrosarcoma, myositis ossificans and heterotopic bone formation of tumoral calcinosis. The bony mass was resected operatively. The pathological study showed the tumor to be a 7 x 4.5 x 3.5 cm hard, nodular mass with a focal attachment of fibroadipose tissue. Microscopically, the lesion was composed of irregular bony trabeculae and fibrotic bone marrow, covered by a cartilagenous cap of variable thickness ( 1 4 mm) Fig. 5A and B). An irregular, densely fibrotic epichondrium focally covered the cartilagenous cap. No histological evidence of malignant transformation was noted. The final histopathological diagnosis was osteochondroma. Pathological studies Fig. 5. A A photomicrograph of the lesional tissue shows a thick, cartilagenous cap covered by fibrous epichondrium. The main tumor mass is composed of irregular bony trabeculae and a fibrotic bone marrow (HE stain x 35). B Another photomicrograph in higher magnification (HE stain x 100) obtained from another area of the lesion demonstrates irregular bony trabeculae and a thin cartilagenous cap D. F a n n e y et al. : Case r e p o r t 415 Discussion Benign exostosis (osteochondroma) is a common bone tumor constituting 9.3% of Dahlin's series. This tumor may occur in any bone, but usually develops in the metaphyseal region of long bones, especially the distal end of the femur. The cervical spine is an unusual location. In the series of 579 osteochondromas reported by the Mayo Clinic, only two instances of osteochondroma in the cervical spine were noted [1]. Benign osteochondroma is the most common benign bone tumor (excepting nonossifying fibroma which also includes fibrous cortical defects), accounting for 40% of the benign lesions in the Mayo Clinic series [1]. Since the tumor is usually asymptomatic, the actual incidence is probably higher. The lesion enlarges by progressive endochondral ossification of a growing cartilaginous cap. On plain films, the bony stalk is noted to project from the surface of a long bone, usually away from the adjacent joint and the lesion appears smaller than its actual size, since the cartilaginous cap is not well seen. When multiple, the condition is known as hereditary multiple exostoses (HME). This entity is transmitted as a single autosomal dominant gene. The cartilaginous cap in any lesion may undergo malignant transformation to chondrosarcoma. The risk of sarcomatous change in solitary osteochondroma and H M E is less than 1% and 10% respectively [1]. Although osteochondromas are often asymptomatic, malignant transformation or encroachment on a nearby joint, vessel, or nerve may necessitate their surgical removal. Review of the literature reveals that neurological complications of benign exostoses are uncommon and most often occur in HME. Spinal cord compression is particularly rare. Madigan et al. [9], reviewed the literature and documented 13 cases of compression of the cervical cord secondary to HME. Pain, tenderness, or recent growth of an osteochondroma should alert the physician to the possibility of malignant transformation. Exostosis bursata (fluid in an adventitial bursa) may mimic this clinical picture and ultrasound has been shown to be helpful in establishing the diagnosis [2]. Most chondrosarcomas arising from exostoses are low grade with subtle malignant features. Consequently, pathological distinction between benign and malignant exostotic chondrosarcoma has been difficult [3]. The surgeon relies heavily on the radiologist not only to differentiate these entities but also to delineate their anatomical relations, since resection will vary accordingly. Although in most cases this distinction can be 173 made by clinical characteristics and plain radiographs [1, 7], many instances occur when the findings are equivocal. Therefore, other imaging modalities have become increasingly important in the preopertive evaluation of exostotic cartilaginous bone tumors. The role of radionuclide imaging appears limited to screening. Hudson et al. [4], found that intense uptake of 99mTc diphosphonate occurred in areas of endochondral ossification in benign exostoses, and uptake in chondrosarcoma occurred in areas of increased osteoblastic activity and hyperemia. Importantly, uptake was not related to amorphous calcification of cartilage. Consequently, large masses of non-ossifying cartilaginous tissue may not appear on the image at all. Hudson also reports that, under the age of 29 years, the intensity of uptake was similar in benign and malignant exostoses. In patients over 30 years of age, intense uptake supported the clinical diagnosis of chondrosarcoma. However, a normal study did not exclude malignancy. Computed tomography (CT), on the other hand, has proved useful in the preoperative differentiation of chondrosarcoma from benign exostoses. Furthermore, CT helps define the anatomical extent and relations of these lesions. Kenney et al. [8], developed differential criteria on CT by depicting internal and peripheral characteristics of cartilaginous tumors as well as their soft tissue extent. CT images of a benign exostosis demonstrated a bony mass with a sharply defined periphery, a more lucent but organized center with cortex and medullary cavity continuous with the bone from which the lesion arose and a thin cartilaginous cap. Criteria suggesting chondrosarcoma included a prominent soft tissue mass with a more dense heterogeneously calcified center, a thick (greater than 3 cm) cartilaginous cap and adjacent bone or soft tissue abnormality. CT also has been useful in predicting the histological grade of chondrosarcoma. Rosenthal et al. [10], studied 20 cases of chondrosarcoma and concluded that CT effectively defined several features useful in predicting histological grade, including (a) morphology of calcification; (b) distribution of calcification; (c) pattern of tumor growth and (d) presence of necrosis. They also found that tumor/soft tissue margins were usually well defined regardless of the grade. Other authors have been less successful. Hudson et al. [6J, studied 31 CT images of cartilaginous tumors and showed that CT measurement of the actual cartilage cap was often imprecise, especially in the range of 1.5-2.5 cm. They concluded that CT was not helpful in distinguishing benign exos- 174 toses with thick cartilage caps f r o m c h o n d r o s a r c o mas with relatively thin caps. F u r t h e r m o r e , they felt that it is often difficult to delineate the outer surface o f the cartilaginous cap f r o m adjacent normal tissue. H u d s o n et al. [5] r e p o r t e d that a thick cartilaginous cap o f an exostotic c h o n d r o s a r c o m a was detected on magnetic resonance ( M R ) b u t not CT. The m a x i m u m cartilage thickness on p a t h o logical examination o f this r e p o r t e d c h o n d r o s a r c o m a was 1.5 cm. However, a benign exostosis with a cartilage cap o f 0.2 cm thickness was not detected by C T or M R I . M R was superior to C T in delineating b o n e t u m o r s f r o m adjacent muscle and in showing the relationships to bone o f the deep margins o f some soft tissue t u m o r s [5]. H y a line cartilage o f articular surfaces shows a bright signal intensity on magnetic resonance imaging. Fibrocartilage, in contrast, has a low signal intensity and appears as a d a r k or dark-grey structure. The cartilage cap a r o u n d an o s t e o c h o n d r o m a is composed o f hyaline cartilage which should have a bright or light grey signal. In this o s t e o c h o n d r o m a o f the neck, the cartilaginous cap was thin and the variable thickness o f the cap (1-4 mm) was not detected by M R . The main bulk o f osteochond r o m a on M R is n o t e d as a mass o f mixed d a r k and bright signals. The d a r k - a p p e a r i n g areas represent ossified cartilage or b o n y trabeculae interspersed by the bright signals o f fibrous connective tissues (Figs, 3 and 4). In summary, a large mass in the neck o f a 33-year-old m a n radiologically and histologically c o n t a i n e d b o n y and cartilaginous elements and involved the posterior elements o f several cervical D. Fanney et al.: Case report 415 vertebrae. T h e lesion p r o v e d to be a benign osteoc h o n d r o m a in an unusual location, m a k i n g its distinction f r o m c h o n d r o s a r c o m a and several other entities difficult by plain films alone. The differential diagnosis was offered and the diagnostic radiological features o f o s t e o c h o n d r o m a were described. The relative values o n scintigraphy, c o m p u t e d tom o g r a p h y and magnetic resonance imaging in the evaluation o f cartilaginous t u m o r s were discussed. References 1. Dahlin DC (1978) Bone tumors. General aspects and data on 6,221 cases. 3rd ed. Charles C Thomas, Springfield, p 18 2. E1-Khoury Gay (1979) Symptomatic bursa formation with osteochondromas. AJR 133:895 3. Henderson ED, Dahlin BC (1963) Chondrosarcoma of bone: a study of 288 cases. J Bone Joint Surg 45 A: 1450 4. Hudson TM, Chew FS, Manaster BJ (1983) Scintigraphy of benign exotoses and exostotic chondrosarcomas. AJR 140:581 5. Hudson TM, Hamlin DJ, Enneking WF, Pettersson H (1985) Magnetic resonance imaging of bone and soft tissue tumors. Skeletal Radiol 13:134-136 6. Hudson TM, Springfield DS, Spanier SS (1984) Benign exostosis and exostotic chondrosarcoma: evaluation cartilage thickness by CT radiology. 152:595 7. Huvos AG (1979) Bone tumors: diagnosis, treatment and prognosis. WB Saunders, Philadelphia, pp 139-152; 206-237 8. Kenney PJ, Gilila LA, Murphy WA (1981) The use of computerized tomography to distinguish osteochondroma and chondrosarcoma. Body CT 139:129 9. Madigan R, Worral T, McClain EJ (1974) Cervical and compression in hereditary multiple exostoses. J Bone Joint Surg 56-A:401 10. Rosenthal DI, Schiller AC, Manken HJ (1984) Chondrosarcoma: correlation of radiologic and histologie grade. Radiology 150:21