Introduction

Osteochondroma is the most common benign tumor of the bone. It is frequently located in the metaphyses of the long bones, and it is an ectopic development of cartilage growth plates. This tumor constitutes 10–15% of all bone tumors and 20–50% of benign bone tumors [1]. It typically occurs in young adolescent patients, because it is a disease of cartilage growth plates and typically does not develop after skeletal maturity [2]. Most patients with this disease have no subjective symptoms, and there is a low rate of malignant transformation, so affected patients often do not undergo regular follow-up with their physicians.

Osteochondroma of the spine is rare and comprises only 1.3–4.1% of all osteochondromas [3]. Only 0.5–1% of spinal osteochondromas may develop insidious but progressive symptoms of myelopathy, radiculopathy, or both, resulting in serious neurological sequelae if not diagnosed and treated early. However, which cases may develop myelopathy is not known. Moreover, indications for the excision of asymptomatic lesions are controversial [2, 4, 5]. In this report, we describe a case of cervical osteochondroma that occurred in a patient with hereditary multiple osteochondromas (HMEs) whose magnetic resonance imaging (MRI) findings obtained before neurological dysfunction developed revealed a cartilage cap adjacent to the cervical cord. This case suggests that if a cartilage cap is observed, especially prior to skeletal maturity, continued grow of the lesion can be expected, and follow-up is required to insure such growth does not compromise adjacent structures.

Case report

An 8-year-old girl with HME presented with a tumor on her cervical spine. She had no significant neurological symptoms. Radiographic images showed the tumor located in the C3 spinous process (Fig. 1a). MRI revealed that the tumor arose from the C3 spinous process and did not extend into the vertebral body (Fig. 1b). The tumor had a cartilage cap (arrowhead) on the spinal canal that showed high signal intensity on axial T2-weighted MRI and was thin, measuring 2 mm in thickness (Fig. 1c). We diagnosed the tumor as an osteochondroma and planned to follow the patient every 6 months. However, she dropped out from regular follow-up.

Fig. 1
figure 1

Radiographic assessment of the cervical spine at the first visit. a Radiograph of the cervical spine showed an osseous mass located in the C3 spinous process. b Sagittal T2-weighted (repetition time ms/echo time ms =2700/100) MRI of the cervical spine revealed a tumor arising from the C3 spinous process. c Axial T2-weighted (4009/100) MRI of the cervical spine revealed that the tumor was growing out of the spinal canal with a cartilage cap on the spinal canal (arrowheads)

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Three years later, she experienced neck pain and a clumsy hand for 3 months. She was not able to play a musical instrument well. Clinical examination revealed numbness in the left upper extremity. The patient also mentioned a sensory impairment in her left palm. There was no history suggestive of bladder or bowel involvement. A comparison of current and previous radiographic images showed that the tumor had enlarged (Fig. 2a). Computed tomography (CT) and MRI showed a bony mass arising from the C3 spinous process and extending into the spinal canal, compressing the spinal cord (Fig. 2b–d). However, the cartilage cap appeared to be thinner in current images than in previous images. Sagittal T2-weighted MRI of the cervical spine showed a lesion with high signal intensity.

Fig. 2
figure 2

Preoperative radiographic assessment of the cervical spine. a Radiograph of the cervical spine showed that the tumor was enlarged compared to its size at the patient’s first visit. b Sagittal CT demonstrated an osseous tumor arising from the spinal process of C3 and extending to the spinal canal. c Sagittal T2-weighted (4200/103) MRI of the cervical spine revealed that the tumor with extension into the spinal canal compressed the cervical cord at the level of C3/4 vertebrae. d Axial T2-weighted (4600/100) MRI of the cervical spine revealed that the tumor compressed the cervical cord at the level of C3/4 with high signal intensity in the cervical cord (arrowheads)

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We diagnosed the patient with cervical myelopathy caused by compression of the spinal cord due to the tumor, and we performed a C3 laminectomy and C4 partial laminectomy with a posterior approach. A skin incision was made immediately superior to the C2–C4 spinous process. During piecemeal resection of the tumor originating from the C3 spinous process, the C3/C4 intervertebral space was expanded while leaving the tumor in the midline area. While thinning the bone tumor at the C3 with an airtome, the C3 vertebral arch was excavated at a width of 18 mm, lifting the tumor and vertebrae on the left and right. The part of the superior margin of the C4 vertebra protruding into the spinal canal was similarly excavated with an airtome to a width of 18 mm, and the superior margin of the C3 bone tumor and C3 vertebral arch were lifted and excised as a single mass. Hematoxylin-eosin staining of the resected tumor showed a regular cartilage cap merged into the underlying bone. The superficial portion of the cartilage cap contained chondrocytes with a columnar arrangement toward the base, where enchondral ossification occurred (Fig. 3). After the operation, the patient experienced immediate improvement in her preoperative symptoms. At the 12-month follow-up, there was no tumor recurrence. However, radiographic images showed cervical kyphosis (Fig. 4).

Fig. 3
figure 3

Hematoxylin-eosin staining of the resected tumor showed the hyaline cartilage cap lies onto the bony trabeculae with no evidence of malignancy

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Fig. 4
figure 4

Postoperative radiograph showed cervical kyphosis

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Discussion

The etiology of an osteochondroma is thought to be due to an initial separation of a cartilage fragment from a physis. Persistent growth of this cartilaginous fragment and its subsequent enchondral ossification result in a subperiosteal osseous excrescence with a cartilage cap that projects from the bone surface [6]. The cartilage cap resembles a growth plate with columns or clusters of chondrocytes evenly distributed and maturing in an enchondral process. Therefore, osteochondromas enlarge from growth at the cartilage cap, identical to a normal physeal plate [1].

Spinal osteochondromas are thought to arise from excessive cartilaginous tissue of secondary ossification centers in the posterior elements of the spine [7], namely the tip of the spinous or transverse process [8]. Though any part of the vertebrae can be involved, the posterior arch is the most commonly affected. The incidence of osteochondroma in the spine is reported to be rare [9]. The incidence of spinal involvement in HME is about 7–9%, whereas that in solitary osteochondroma is about 1–4% [10, 11]. However, spinal cord compression by an osteochondroma is unusual because the majority of these lesions grow out of the spinal canal [12]. Symptomatic lesions need to be treated surgically, and good results following total resection have been reported [2].

Osteochondromas do not grow after skeletal maturity, and they usually manifest clinically in young adolescent patients. Osteochondromas producing clinical symptoms late in adult life are extremely rare. Osteochondroma of the spine usually occurs during the second to fifth decades of life, but the exact reason for the late presentation of spinal osteochondroma remains unknown [4, 13]. Sakai et al. suggested that the onset of associated degenerative changes in the spine might contribute to the onset of symptoms in the elderly [7]. On the other hand, in the young, tumor enlargement might be a primary contributor to the initiation of myelopathy. Spinal cord compression by an osteochondroma is an unusual and extremely rare phenomenon, but osteochondromas with “posterior components,” such as the posterior arch and spinous process, should undergo careful, regular follow-up. The preoperative radiographic evaluation should comprise MRI and CT to provide optical information with respect to surgical planning and malignant change [4].

The use of MRI to screen all patients who have MHE at least once during the growing years is recommended because the potential exists for serious neurologic injury to occur [5]. However, what kind of case of cervical osteochondroma develops into myelopathy is not known. Our case differs from previously reported ones in that MRI had been obtained before myelopathy developed. The MRI in this case may have suggested a cartilage cap on the spinal canal even though the patient had no symptoms. Such tumors may extend to the spinal canal, resulting in neurologic dysfunction; therefore, careful follow-up until skeletal maturity should be performed.