Foramen magnum osteochondroma causing myelopathy in a patient with hereditary multiple exostoses

INTRODUCTION

Osteochondromas are benign bone tumors occurring in 3% of the general population; they account for 30% of all benign bone tumors.[6] However, intracranial osteochondromas are rare (0.1–0.2% of all intracranial tumors).[7] Of the 31 cases of intracranial osteochondromas reported in the literature, only 1 arose from the foramen magnum.[1,2,4,5,7-9,11,12,14] Here, we present a patient with a foramen magnum/skull base osteochondroma causing spinal cord compression attributed to underlying hereditary multiple exostoses (HMEs).

CASE DESCRIPTION

A 51-year-old male presented with a 12-year history of difficulty climbing stairs, 12 months of clumsiness of both hands, and 9 months of shooting pain into the radial aspect of his left forearm, along with right-handed weakness/grip. He had historically had osteochondromas removed from his right iliac crest and left scapula, 12 and 11 years ago, respectively. He also gave a history of a bony growth on his forearm which had been previously removed.

Diagnostic studies

Plain X-ray of the cervical spine [Figure 1] showed an exostosis at the posterior aspect of the craniovertebral junction; this finding was confirmed on CT scan [Figure 2]. The cervical MR showed severe cord compression from the posteriorly located exostosis, and there was a high signal in the cord on the T2-weighted image [Figure 3].

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Figure 1:: (a) Lateral cervical spine X-ray shows an exostosis at the posterior part of the craniovertebral junction (white arrow). (b) Sagittal T2 WI MRI shows a bony spur from the lip of the foramen magnum (white arrow) pressing on the spinal cord and causing signal changes.

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Figure 2:: Axial CT scan shows the osteochondroma protruding into the cervical canal (white arrow), (a) axial view of foramen magnum, (b) axial view C1.

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Figure 3:: (a) Intraoperative photograph after removing the posterior arch of C1 lamina shows the pointer identifying the tip of the exostosis arising from the posterior lip of the foramen magnum. (b) Intraoperative photograph after removing the osteochondroma shows the decompressed cervical spinal cord.

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Histopathology

The histopathological report confirmed the diagnosis of osteochondroma [Figures 4]. The patient was subsequently sent for genetic analysis which confirmed he had hereditary multiple exostosis (i.e., also called diaphyseal aclasis).

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Figure 4:: Microscopic histology of the osteochondroma lesion sample during the procedure, (a) the perichondrium, (b) the cartilage cap.

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DISCUSSION

Osteochondroma is the most common benign bone tumor. It is a cartilage-tipped exostosis and can be sessile or pedunculated with a cancellous structure that is well formed with a complete cortex. The stalk of an exostosis must be in direct continuity with the underlying cortex and medullary canal to be considered a true osteochondroma.[10] It can occur as a solitary lesion or as part of HME. Any bone which develops endochondral cartilage is susceptible to osteochondromas; they most commonly occur on the lateral side of active growth plates within long bones, but can also occur on the knee, scapulae, pelvis, tarsal, and carpal bones. In patients with HME, osteochondromas tend to be larger and highly irregular.[3,10]

Intracranial osteochondromas are very rare, accounting for 0.1–0.2% of all intracranial tumors.[7] Lotfinia et al. (2012) reported a similar case in which a 73-year-old male presenting with quadriparesis and gait difficulties underwent complete and successful excision of an osteochondroma originating from the foreman magnum.[9]

Hongo et al. (2015) and an additional seven cases (including our report) demonstrated that 43.3% of these lesion originating from the skull convexity, with the remainder originating from the falx cerebri (13.3%), parasellar (10%), posterior clinoid (10%), foramen magnum (6.7%), sella turcica (6.7%), middle fossa (3.3%), petrous bone (3.3%), and suprasellar (3.3%) regions.[1,2,4,5,7,12,14] Venkata et al. (2011) expressed that complete excision of an intracranial osteochondroma is curative.[13]

CONCLUSION

Here, we report a foramen magnum osteochondroma in a patient with HME. Spinal surgeons should be aware that osteochondromas can arise from this location precipitating the onset of cervical myelopathy.