Spinal Osteoid Osteoma Revealed by Radiculopathy: Case Report and Literature Review

BACKGROUND

Osteoid osteoma (OO) represents about 2% to 3% of all bone tumors.¹ It usually occurs in the metaphysis and diaphysis of long bones.² The spine is involved in up to 25% of OOs, particularly posterior elements of the lumbar segment.³ The clinical presentation varies depending on the location of the tumor.

We herein report the case of an OO of the lumbar spine revealed by sciatica. Given the atypical clinical presentation, the infrequency of such a location, and the imaging diagnosis difficulty, our case is worthy to report. The management of this entity was discussed based on a literature review of spinal OO revealed by radiculopathy. The search of articles was performed in Medline, Embase, Scopus, and Cochrane library databases. The following key words were used: ((“Osteoma, Osteoid”) AND (“spine” OR “radiculopathy” OR “sciatica” OR “brachial neuralgia”). Key words referred to medical subject heading (MeSH).

CASE PRESENTATION

A 25-year-old woman presented with low back pain and right L5 sciatica evolving for 6 months. She had no trauma or any relevant family or medical history. There was no history of fever or night sweats. She was experiencing morning stiffness and night pain that interfered with sleep. Pain was not relieved by paracetamol and opioids. Clinical examination revealed lumbar stiffness and no signs of neurological compromise except for the sciatica. Laboratory tests showed an erythrocyte sedimentation rate at 33 mm and C-reactive protein level at 5.3 mg/L.

All laboratory and imaging results, including plain radiography and a lumbar computed tomography (CT) scan, were initially normal.

Magnetic resonance imaging (MRI) performed 10 months after symptom onset revealed a bone marrow edema of the right L5 transverse process, centered by a linear low-intensity image on T1 and T2 weighting (Figures 1A and 1B). However, no diagnosis could be established.

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Figure 1

(A) Axial gadolinium-enhanced fat-suppressed T1-weighted magnetic resonance imaging showing the low-signal intensity lesion (white arrow), centered by a high-intensity round lesion which has strong enhancement, and edema in the surrounding bone marrow (*). (B) Axial T2-weighted magnetic resonance imaging of L5 vertebrae showing a low-signal intensity lesion of the right transverse process, with high-signal intensity peripherally (*) and heterogeneous signal intensity centrally (white arrow). (C) Computed tomography scan showing the lesion arising from right transverse process of L5 vertebrae, revealing the nidus (white arrow) surrounded by dense sclerotic bone in its periphery.

Since pain kept worsening despite analgesics, a second CT scan was performed after 12 months of symptom evolution, using thinner slices on the right transverse apophysis of L5. This CT scan showed a 4 mm cortico-subcortical osteolytic lesion, centered by a hyperdense millimetric nidus, surrounded by an area of osteosclerosis (Figure 1C). These findings led to a diagnosis of OO of the right transverse process of L5.

However, pain was only partially and temporarily relieved with aspirin. Therefore, the patient underwent an en-bloc excision with resection of the right L5 transverse process under general anesthesia. The patient was placed in the prone position on a radiolucent table. We used a posterior midline approach to expose the L5 transverse process under scopic control. An L5 transverse resection was performed with a bone surgical chisel with preservation of the articular capsule of the right L4–L5 articular mass. Histopathology of the intraoperative excised specimens (Figure 2A) confirmed the diagnosis of OO. Lumbar x rays and CT scan were performed the first postoperative day and confirmed the absence of residual nidus (Figures 2B and 2C). Immediate pain relief was reported, and sciatica disappeared within the first postoperative hours, with a persistent remission at 30 months follow up. No complication associated with surgery occurred, and no muscle weakness was observed.

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Figure 2

(A) Bone fragment of the en-bloc excision of right L5 transverse process containing the nidus surrounded by osteosclerosis. (B) Postoperative x rays and (C) CT scan images of lumbar spine showing no residual tumor.

DISCUSSION

We report the case of a 25-year-old woman with an OO located in the L5 right transverse process revealed by right L5 sciatica. Our case is particular by the atypical clinical presentation, the tumor's location in the transverse process, and the occurrence in a female patient.

In fact, OO affects mainly males with a sex ratio of 3:1.^4,5 Tumor distribution in spine regions varies among authors. For most authors, lumbar spine is the most commonly affected segment, followed by cervical and thoracic spine and sacrum.⁶ In a case series of 84 spinal OOs, posterior elements of the spine were 3 times more affected than vertebral body.⁵ Lamina and pedicles on the vertebral arch are most commonly affected, but cases involving the transverse processes have also been reported.^5,7–10

The classic presentation of OO in a spinal location is a painful scoliosis or an isolated spinal night pain alleviated with the use of aspirin or nonsteroidal anti-inflammatory drugs.⁶ Radicular pain, as in our case, appears as a rare clinical picture in spinal OO. To date, there are 19 other reported cases of spinal OO revealed by radicular pain (Table).^6,7,10–18 To our knowledge, only 2 cases of OO of the transverse process revealed by radicular pain have been reported.^10,12

Despite advances in diagnostic technology, the average duration before establishing a diagnosis is 15 to 20 months.¹² Depicting spinal OO on x rays is not an easy task, especially when x rays are performed in early stages of symptoms evolution, where radiographs are often normal.¹² In more advanced conditions, we might identify the common aspect of OO, which is an area of bone sclerosis surrounding a small radiolucent central region corresponding to the nidus.² However, in our case, radiographs were still normal after a year of disease evolution. This might be explained by the complex anatomy of the spine and the small size of the tumor, making the osteolytic lesion almost not visible on plain radiographs.¹⁹

MRI and CT are more sensitive than x rays for detecting soft tissue and bone marrow abnormalities adjacent to OO.¹⁹ However, in our case, MRI could not individualize the nidus, which was drowned in edema and osteosclerosis. Moreover, when the nidus is not identified, images of perilesional edema provided with MRI might be confused with an aggressive tumor-evoking aspect or with images of bone infection.²⁰ In such cases, CT scan might redress the diagnosis. CT scan remains the most specific diagnostic imaging modality to analyze the nidus with the varying degrees of perinidal sclerosis.^20,21

Our case emphasizes the value of CT scan in the diagnosis of OO by giving thin cross-sectional images of the suspected area. In a case reported by Ono et al²¹, CT with 1-mm slices showed the nidus with a clear, round osteolytic lesion ossification inside, leading to a diagnosis of OO, although the nidus had been overlooked in CT with 5-mm slices because of its small size, and the patient was diagnosed with lumbar spondylolysis on initial MRI and CT.

Spinal OO can be treated either with surgical intervention or minimally invasive interventions.⁵ Surgical options include intralesional curettage or marginal or en-bloc excision.^4,5 Minimally invasive interventions consist of radiofrequency thermo-ablation (RFA) or CT-guided core excision.²²

RFA has been proven to be effective and safe, with less complications and shorter hospitalization than surgical treatment.^22,23 However, RFA cannot be performed safely if there is neurological impairment, if cortical bone around CT lesions is not intact, or if the cerebrospinal fluid between the lesion and nerve root or spinal cord is not sufficient (<1 mm) on MRI. In cases like ours in which osseous tumor infiltration produces radicular nerve root irritation and radicular symptoms, wide surgical excision of the tumor and surrounding tissue is the treatment of choice.^12,22,23 Moreover, en-bloc excision is a guarantor of lower risk of recurrence than piecemeal excision, curettage, and RFA, since it leads to a complete removal of the nidus.^5,22

CONCLUSIONS

Radiculopathy is an uncommon clinical presentation in spinal OO that might be responsible for a prevalent diagnosis delay. Although not frequent, OO should be suspected in all young patients with inflammatory spinal symptoms even if x rays are normal.

Our case emphasizes the better accuracy of CT scan in detecting OO compared to MRI and x rays. In case of any doubt, it is necessary to resort to the thin section CT scan which could be guided with MRI. Treatment depends on location. Surgical removal can be performed safely in spinal OO within posterior elements. RFA can be a good alternative if there is no neurological impairment.

KEY MESSAGES

• Although radicular pain revealing spinal osteoid osteomas is clinically uncommon, the diagnosis should always be suspected and imaging findings interpreted with caution especially in young patient with inflammatory and chronic symptoms.

• Osteoid osteoma may display misleading imaging findings, and it can be difficult to differentiate osteoid osteoma from other conditions such as infection or other benign or malignant tumors.

• To make the correct diagnosis, it is necessary to identify the nidus, and it is important to be familiar with the radiologic findings of osteoid osteoma and its mimics.