Radiology

Case 35: Contributed by Dr. Bhavesh Popat

Other Cases

Case Report :

A six-year-old male child presented with a history of severe pain in the right leg around the knee joint. The pain which had been present for over eight months, had become more severe in the past two months and was worse at night. A detailed clinical examination revealed tenderness just below the knee joint. On the basis of a typical clinical history, a provisional clinical diagnosis of an osteoid osteoma was made. Plain radiographs were performed which demonstrated a fairly well-defined radiolucent area in the right tibial metaphysis surrounded by a sclerotic rim which confirmed our diagnosis of osteoid osteoma (Fig 1).

Fig 1

 

The patient was referred for radiofrequency (RF) ablation of the lesion. MRI of the right leg was done which would form the baseline for future follow up (Fig 2).

 

Fig 2

Under deep sedation, nidus localization was done using thin section (3 mm) CT and CT fluoroscopy. After discussions with the entire team, a lateral approach was thought to be the best access site to place a 13G coring bone biopsy needle (Cook) in the nidus of the lesion to avoid going through the muscular compartment as also avoid injury to neurovascular bundle (Fig 3)

Fig 3

Once we were satisfied that our biopsy needle was placed in the lesion, an 18-gauge, 10- cm-long, bipolar probe system (Pro Surge Micro, Celon) was introduced through the biopsy needle (Fig 4).

Fig 4

This bipolar RF probe had an uninsulated electrode length of 15 mm at the tip. After ascertaining that the tip had been accurately positined in the nidus of the lesion, the lesion was ablated. The total ablation time was 5 mins while we applied a mean energy of 1 Kilojoules to the lesion. Post procedural management included diclofenac suppository to alleviate pain for 1 day and oral antibiotics. Complete clinical success was achieved as patient showed complete relief of symptoms 36 hours after the procedure. Post procedure contrast MR was done after one week which showed complete lack of nidal enhancement reflecting radiological success. The patient was symptom free at two month follow up.

DISCUSSION:

Osteoid osteoma, first described in 1935, is a painful bone lesion that accounts for 10% -12% of benign bone tumors. It mainly develops in immature bone in children and young adults.

Clinically, pain is the most common presenting symptom which typically worsens at night and is often relieved by antiinflammatory agents. However, long term medical therapy may be unacceptable because of refractory pain and complications of chronic anti-inflammatory agents . In addition, osteoid osteoma may occur in articular or periarticular areas of bone. In such cases, medical therapy may be inadequate and more aggressive interventions are necessary.

The Definitive treatment of osteoid osteoma involves open surgical resection or localization of the lesion under CT guidance and removal or destruction of the tumor nidus. Standard surgical treatment in the form of en bloc resection has been considered an efficacious treatment for many years. However, open surgical resection has the disadvantages of the morbidity of a surgical procedure and the risk of fracture after the removal of the tumor nidus. Fracture is a risk because the large size of the resultant bony defect causes a large stress riser. Open surgical resection is also occasionally problematic, partly because of intra operative difficulty of lesion localization combined with the necessity to completely remove the nidus. Bone removal may be of such an extent as to warrant internal fixation or bone grafting. Because many osteoid osteomas present in long weight bearing bones, significant activity restriction may become necessary. Also, significant bone removal in the articular and epiphyseal lesions may require arthrotomy and impair growth and mobility. These issues may be particularly problematic in the younger population affected by osteoid osteoma. Also pain recurrence in patients following surgery has been reported in about 12% of cases.

Since Rosenthal first described thermal ablation of osteoid osteoma in 1992, this minimally invasive therapy has been increasing, and several studies have been reported. In the most considerable study published by Rosenthal et al: an initial clinical success rate could be achieved in 91% with the residual or recurrent pain being 9%. Three years later Rosenthal et al published another paper comparing 87 consecutive surgical resections of osteoid osteoma with 38 RF ablation procedures with as many as 2 years follow up. The authors found no difference between the groups in recurrence rate or persistent pain. Thermal ablation reduces duration of hospital stay and is more cost effective than the traditional en bloc resection.

In conclusion, percutaneous treatment of osteoid osteoma should be considered in patients who have failed medical therapy, are being considered for surgical resection, or have failed previous surgery and have recurrent symptoms.