On spinal osteochondromas

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✓ Osteochondromas (or osteocartilaginous exostoses) make up about 30% to 40% of benign bone tumors. Most are solitary lesions but some are multiple, usually with autosomal dominant inheritance. From 1% to 4% of osteochondromas occur in the spine, where they can cause a variety of signs and symptoms, including those of spinal cord or spinal root compression. The authors present five patients with osteochondromas of the spine and review the findings together with those of over 130 cases reported since 1907. The cases were divided into: 1) spinal osteochondromas in patients with multiple osteochondromas, and 2) solitary osteochondromas occurring in the spine. The age (mean ± standard error of the mean) of patients in the first group was 21.6 ± 1.8 years compared to 30.0 ± 2.1 years for those in the second group (p < 0.02). There was a significant male predominance overall (M:F = 2.5:1; p < 0.0005). In both groups, one-half of the lesions involved the cervical spine. Symptoms are caused by pressure on adjacent structures. Spinal cord compression was reported more than twice as frequently in the multiple osteochondroma group as in the single osteochondroma group (77% vs 33%; p < 0.0005). Computerized tomography (CT) is the imaging procedure of choice. In both groups, the majority of surgically treated patients (90% and 88%, respectively) improve, with about three-quarters of the improved patients having no residual disease or only minor deficits.

Abstract

✓ Osteochondromas (or osteocartilaginous exostoses) make up about 30% to 40% of benign bone tumors. Most are solitary lesions but some are multiple, usually with autosomal dominant inheritance. From 1% to 4% of osteochondromas occur in the spine, where they can cause a variety of signs and symptoms, including those of spinal cord or spinal root compression. The authors present five patients with osteochondromas of the spine and review the findings together with those of over 130 cases reported since 1907. The cases were divided into: 1) spinal osteochondromas in patients with multiple osteochondromas, and 2) solitary osteochondromas occurring in the spine. The age (mean ± standard error of the mean) of patients in the first group was 21.6 ± 1.8 years compared to 30.0 ± 2.1 years for those in the second group (p < 0.02). There was a significant male predominance overall (M:F = 2.5:1; p < 0.0005). In both groups, one-half of the lesions involved the cervical spine. Symptoms are caused by pressure on adjacent structures. Spinal cord compression was reported more than twice as frequently in the multiple osteochondroma group as in the single osteochondroma group (77% vs 33%; p < 0.0005). Computerized tomography (CT) is the imaging procedure of choice. In both groups, the majority of surgically treated patients (90% and 88%, respectively) improve, with about three-quarters of the improved patients having no residual disease or only minor deficits.

Osteochondroma, also known as “osteocartilaginous exostosis” or just “exostosis,” is a common tumor affecting bone, making up about 8.5% of all bone tumors and about 36% of benign ones.11 Osteochondroma occurs in a solitary form or in a multiple form called “multiple exostoses” or “osteochondromatosis.” Multiple exostoses can occur sporadically but are most often inherited as an autosomal dominant trait which is then termed “hereditary multiple exostoses.” Spinal osteochondromas can arise as solitary lesions or in the context of multiple exostoses or hereditary multiple exostoses. In this paper, we present five cases of spinal osteochondroma and review them together with over 130 additional cases reported in the literature since 1907.

Clinical Material and Methods
Patient Population

The files of the pathology department of The Methodist Hospital, Houston, Texas, were searched for all cases coded as osteochondroma managed between January, 1965, and September, 1990. Because these records were found to be incomplete, the ICD-9 coding files of the Medical Records Department were also searched for all cases recorded as benign bone tumor of the spine treated from 1972 to 1984. A total of 169 cases of osteochondroma were thus located, of which five (3.0%) were spinal. The patients' charts, x-ray reports, x-ray films (where available), and histological slides were reviewed. There were three male and two females, aged 10 to 48 years. One patient presented with radiculopathy, one with local pain, two with asymptomatic palpable masses, and one was discovered incidentally during radiological workup for spinal stenosis.

Literature Review

We used MEDLINE searches and the bibliographies of published papers to obtain as many references as possible. Each reference found was reviewed for recorded clinical, historical, and pathological details. There were a total of 78 cases of solitary spinal osteochondroma and 16 cases where multiplicity was not explicitly mentioned but where the remainder of the clinical data were consistent with a solitary osteochondroma. There were also 32 cases of spinal osteochondroma in patients with multiple exostoses, hereditary or not. Finally, there were 10 cases for which not enough information was available to decide whether the lesion was solitary or occurred in a patient with multiple exostoses. Most of these references can be found in several articles with literature reviews.3,4,7,15,27,35*

Data Analysis

The patients were separated into two groups: those with multiple exostoses who presented with a spinal osteochondroma; and those with solitary osteochondroma located in the spine. The pooled t-test and the chi-squared test were used for the comparison of means and proportions, respectively.

Illustrative Cases
Case 1

This 48-year-old woman complained of left-sided neck and shoulder pain that had worsened over 3 years. Radiological evaluation at the onset of her symptoms had been inconclusive. Physical examination revealed limitation of all neck movements and tenderness on the left side of the neck, as well as pain radiating to the upper border of the left shoulder. There was no neurological deficit. The clinical impression was that of a left-sided C-4 radiculopathy. Myelography revealed an extradural block at the C-4 level. At laminectomy, a bone lesion with a cartilaginous cap was found arising from the left lateral mass of the C-3 vertebra; it compressed the left C-4 nerve root. This lesion was removed in a piecemeal fashion. Histological evaluation was typical of an osteochondroma.

Case 2

This 16-year-old boy had undergone resection of an osteochondroma of the T-12 vertebra at another institution 2 years prior to admission, but had noticed regrowth of the lesion over 3 to 4 months. The mass was completely asymptomatic. On plain x-ray films of the spine, a 6-cm bone lesion was seen located to the right of T-12; its exact origin could not be identified. On computerized tomography, it was found to arise from the right pedicle of T-12. At operation, the neural arches from T-9 through L-2 were resected and the tumor was removed along with the pedicle. Harrington rods were placed from T-9 to L-2 and an iliac-crest bone graft was applied.

Results

All five of our patients underwent tumor resection. The two whose lesions caused local or radicular pain were free of symptoms following resection and have had no recurrence. There has been no tumor recurrence in the other two who presented with a mass or the patient with the incidental lesion.

Discussion
Etiology

Osteochondromas are believed to arise through lateral displacement of a portion of the epiphyseal growth cartilage. This results in a bone-like outgrowth capped by cartilage (Fig. 1), the cortex and medullary cavity of which are contiguous with those of its bone of origin. Therefore, osteochondromas do not occur in bones that develop through membranous ossification, such as the cranial vault. The osteochondroma grows at its tip as the cartilage undergoes ossification, and if the cartilaginous cap is incompletely resected, the osteochondroma can recur. Given their origin, osteochondromas are better considered as hamartomas than as true neoplasms.

Fig. 1.
Fig. 1.

Photomicrograph of a histological section through a spinal osteochondroma demonstrating the cartilaginous cap (arrows) as well as the bone-like component of the lesion. Masson trichrome, × 2.4 (bar = 0.5 cm).

Incidence

Both solitary and multiple osteochondromas affect males more frequently than females, demonstrating a male:female ratio of about 1.5:1; most patients are 20 years of age or younger.11,28,37 Patients with multiple osteochondromas account for approximately 12% of all cases.11

Osteochondromas affect mostly the long bones. Only 1.3% to 4.1% of solitary osteochondromas arise in the spine,11,16,37 where they make up 0.4% of intraspinal tumors13 or 3.9% of solitary spinal tumors.8 About 9% of patients with hereditary multiple osteochondromas have spinal lesions.39

Table 1 lists the general characteristics of spinal osteochondroma, based on cases that could be assigned either to the multiple exostosis category (hereditary or sporadic) or to the solitary category. Overall, there were 71 males and 28 females, showing a significant male predominance of 2.5:1 (p < 0.0005). The same was true for each group of patients, but the male predominance was significant only in the group with solitary osteochondroma (3:1, p < 0.0005) and not in the group with multiple exostoses (1.8:1, 0.1 < p < 0.2). Patients with multiple exostoses who presented with a spinal osteochondroma were, on average, significantly younger than patients with only a solitary osteochondroma of the spine (21.6 ± 1.8 vs. 30.0 ± 2.1 years, p < 0.02).

TABLE 1

Spinal osteochondromas in patients with multiple and solitary osteochondromas*

FactorMultiple ExostosesSolitary Exostosis
no. of cases32 96 
M:F ratio1.8:1 (20:11) 3:1 (51:17) 
age (yrs)21.6 ± 1.8(32) 30.0 ± 2.1 (67) 
location
 cervical16 32 
 thoracic12 17 
 lumbar4 15 
 sacral0 0 
 coccygeal0 1 
 total(32) (65) 

Numbers in parentheses indicate the number of patients for which the given information was available. Because of incomplete data, these numbers do not always add up to the total number of patients in each of the two groups.

Means ± standard error of the means.

Natural History

In unselected cases, spinal osteochondromas only rarely cause neurological symptoms. Only one of 16 patients reported by Cohen, et al.,8 had paresthesias, while only two of 14 patients described by Geschickter and Copeland16 had evidence of spinal cord compression. Solomon39 reported no spinal cord or root compression in his series of 52 patients with hereditary multiple exostoses, of whom 9% had spinal osteochondromas. Therefore, the large number of patients with neurological disease in the literature may reflect reporting bias.

Recurrence or a sudden acceleration in the growth of an osteochondroma may herald malignant transformation, which occurs in about 1% of solitary and approximately 10% of multiple cases.37 Of 635 chondrosarcomas of bone recorded at the Mayo Clinic,8 seven had arisen in a spinal osteochondroma; five of these patients had multiple exostoses and two had solitary osteochondroma. A few additional cases are recorded.9,10

Distribution

In both groups, about half of the spinal osteochondromas are located in the cervical spine (Table 1). This constitutes a significant overrepresentation since the cervical spine contains only 23% of all the vertebrae (p < 0.005 and p < 0.0005 for patients with multiple exostoses and solitary cases, respectively). Among the cervical vertebrae, C-2 is the most frequent site, being involved eight times in each group. In the patients with solitary osteochondroma, there is also a significant underrepresentation of the thoracic spine, which was the site of only 26% (17) of 65 lesions but contains 40% of all the vertebrae (p < 0.05), Interestingly, the presence of more than one spinal osteochondroma is described in only a few patients with multiple exostoses.1,15,19,38

This squewed distribution of spinal osteochondromas may be related to the mobility of the various segments of the spine. The cervical spine is the most flexible of the spine's mobile segments, whereas the thoracic spine is the least flexible.5 Greater mobility and flexibility are associated with greater stress on the vertebrae, which could lead in turn to microtrauma to the epiphyseal cartilage and displacement of a portion thereof. Once the osteochondroma is thus established and growing, it may be more likely to traumatize neural structures if it is located on a more mobile vertebra.

Neuroradiographic Studies

On plain x-ray films, an osteochondroma typically appears as a pedunculated or sessile bone-like projection, the cortex and spongiosa of which are contiguous with the underlying bone. At the point of attachment, the cortex of the bone of origin flares into the cortex of the osteochondroma. This feature is considered pathognomonic.28 Flecks of calcification can be seen in the area of the cartilaginous cap. Spinal osteochondromas are more difficult to detect on plain x-ray films, probably because of the complex image formed by the spine. Among the 80 cases for which results of routine x-ray studies were described, only 17 films (21%) were considered diagnostic, 51 (64%) showed only nondiagnostic anomalies, and 12 (15%) were interpreted as normal. Myelography will show evidence of extradural compression in almost all patients with neurological signs or symptoms; only a few such patients with a normal myelogram have been reported.14,24,25,34

Computerized tomography is the imaging modality of choice. Not only can it demonstrate the cartilaginous and osseous components of the tumor, thereby allowing a radiological diagnosis, but it also clearly defines the tumor's extent and its relationship to the vertebral and neural elements of the spine (Fig. 2).14,27,28,41 The same holds true for magnetic resonance imaging.14,29,44

Fig. 2.
Fig. 2.

Computerized tomography scans of the osteochondroma depicted in Fig. 1. There is an irregular sessile bone-like mass arising from the abnormally enlarged right lamina of L-4.

Symptoms

Myelopathy predominates in patients both with multiple and with solitary osteochondromas (Table 2), but is significantly more frequent in the former (24 (77%) of 31 cases vs. 23 (34%) of 68 cases, p < 0.0005). The difference in the mean duration of symptoms was not significant (33.3 ± 12.9 vs. 18.1 ± 3.4 months, 0.1 < p < 0.2).

TABLE 2

Presentation and outcome of patients with spinal osteochondroma*

FeatureMultiple ExostosesSolitary Exostosis
no. of cases31 68 
duration of symptoms (mos)33.3 ± 12.9 18.1 ± 3.4 
myelopathy24 23 
 paraplegia/paresis14 11 
 tetraplegia/paresis4 7 
 hemiplegia/paresis2 0 
 Brown-Séequard syndrome2 1 
 unclassifiable2 4 
radiculopathy3 13 
Horner's syndrome1 4 
mass (± mass effect)3 18 
 asymptomatic mass0 11 
pain5 25 
 pain only1 12 
sudden death0 1 
incidental finding2 3 
surgical outcome
 major improvement22 28 
 improvement3 10 
 not improved3 5 

Because a patient could present with more than one sign or symptom, the sum of the subcategories exceeds the total number of patients in both groups.

Mean ± standard error of the mean.

Outcome was not specified in all patients. Furthermore, patients were excluded whose lesions were discovered incidentally, who presented with sudden death, or with an asymptomatic mass.

Neurological disease is the result of progressive encroachment of the slowly expanding osteochondroma upon neural structures so that even a tumor located within the spinal canal can achieve impressive dimensions (Fig. 3). However, in some cases, the onset of symptoms was acute after sudden hyperextension of the spine26 or after a fall.44 Three patients had at least some elements of Brown-Séquard syndrome.2,6,22 In one patient, the complex neurological picture was initially diagnosed as Friedreich's ataxia.18 Horner's syndrome was also occasionally present,2,12,21,40,42 presumably due to compromise of paravertebral sympathetic centers. An osteochondroma of the odontoid process caused sudden death in one patient secondary to subtotal transection of the spinal cord.36

Fig. 3.
Fig. 3.

Illustration demonstrating that even an osteochondroma located in the spinal canal can reach impressive dimensions. (Reproduced from Ochsner EH, Rothstein T: Multiple exostoses, including an exostosis within the spinal canal with surgical and neurological observations. Ann Surg 46:608–616, 1907, with permission from J. B. Lippincott Co.)

Anterior spinal osteochondromas in the neck can also present as a pharyngeal mass,31 as a “calcified goiter,”21 or with hoarseness38 or dysphagia.23,33 Compression of the common carotid, subclavian, or vertebral arteries can occur with cervical osteochondromas15,21 but this does not appear to be associated with stroke, probably due to the slow rate of occlusion by the slowly growing osteochondroma. Bulky osteochondromas arising from a rib but located close enough to the spine (at the head of the rib, at the costovertebral junction) can erode the vertebrae or grow into the spinal canal through an intervertebral foramen, causing myelopathy.10,17,20,30,43

Operative Results

Surgical outcome is summarized in Table 2. Of the 71 surgical cases, 63 (89%) improved. Most patients had complete disappearance of their deficits or only minor residual deficits. Even patients with significant and long-standing deficits can improve; for example, one of the first patients successfully operated on for a spinal osteochondroma made a slow but substantial recovery over 9 years after developing tetraparesis caused by a large osteochondroma of C-2 (Fig. 3).32 Standard surgical approaches to the various spinal levels are used. The main difficulty lies in the bone-like, rock-hard consistency of the tumor, which often calls for the use of drills and chisels in the immediate vicinity of delicate neural structures. Incomplete excision of the cartilaginous cap can lead to recurrence. This has been described as early as 6 months34 and as late as 14 years postoperatively.45

Conclusions

Symptomatic spinal osteochondromas are rare occurrences in an individual surgeon's experience. However, a considerable body of literature on the subject has accumulated over the last eight decades. These cases can come to medical attention with a broad spectrum of presentations ranging from an incidental x-ray finding to sudden death. Computerized tomography is the imaging procedure of choice. In the majority of patients with myelopathy or radiculopathy, surgery produces gratifying results; malignant transformation is a very rare event. It is quite likely that many spinal osteochondromas spend their lives in complete asymptomatic obscurity.

References

A complete list of references is available from the authors on request.

Article Information

Address reprint requests to: Gary K. SeGall, Ph.D., M.D., Department of Pathology, MS 205, The Methodist Hospital, 6565 Fannin Street, Houston, Texas 77030.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Photomicrograph of a histological section through a spinal osteochondroma demonstrating the cartilaginous cap (arrows) as well as the bone-like component of the lesion. Masson trichrome, × 2.4 (bar = 0.5 cm).

  • View in gallery

    Computerized tomography scans of the osteochondroma depicted in Fig. 1. There is an irregular sessile bone-like mass arising from the abnormally enlarged right lamina of L-4.

  • View in gallery

    Illustration demonstrating that even an osteochondroma located in the spinal canal can reach impressive dimensions. (Reproduced from Ochsner EH, Rothstein T: Multiple exostoses, including an exostosis within the spinal canal with surgical and neurological observations. Ann Surg 46:608–616, 1907, with permission from J. B. Lippincott Co.)

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