Scoliosis secondary to spinal osteoblastoma

Clinical History

A 21-year-old man came to our outpatient clinic with progressive scoliosis and back pain that did not improve with the intake of non-steroidal anti inflammatory drugs (NSAID).

Imaging Findings

Plain film showed short thoracic dextroscoliosis with a doubtful sclerotic lesion on the left side of T6. Old films (3 years ago) showed that the scoliosis was already present without sclerosis (Fig. 1).
MRI showed an expansile bone lesion located in the lamina and left facet of T6 with a low signal intensity in T1WI and T2WI. Contrast-enhanced FS T1WI demonstrated heterogeneous enhancement of the lesion with an arterial and early dynamic enhancement type 1 curve (Fig. 2 and 3). The lesion was surrounded by marked oedema of the vertebral bodies and posterior elements of T5, T6 and T7, extending to neural foramenes, para-spinal muscles and posterior left ribs. Facing the findings, a complementary CT scan was performed confirming an expansile bone lesion with a mineralised bone matrix associated with enlargement and sclerosis of the posterior ribs, spinous process, interspinous ligament calcification and secondary dorsal kyphosis. (Fig. 4).

Discussion

Plain films are the initial method of choice for the evaluation of scoliosis. Atypical scoliosis need further imaging procedures to rule out secondary causes of scoliosis. Indications for MR imaging in a patient with scoliosis are: age <10 years, back pain, unusual curve pattern, rapid curve progression, neurological deficiency, neck stiffness and headache [1]. In our patient, MR imaging was obtained because of progressive painful scoliosis and short curve. Once the bone lesion was identified in MR imaging, a CT scan was performed to characterise the lesion, to assess the extent of osseous involvement and the degree of cancellous and cortical bone loss.
The slow evolution of the lesion, at least 3 years, with sclerosis, bone remodelling together with the absence of soft tissue mass or personal history of cancer made malignancies such as osteoblastic metastases and osteosarcoma unlikely. In the posterior spinal elements without aggressive appearance differential diagnosis should include: chondroblastoma, osteoid osteoma and osteoblastoma [2]. The lesion didn’t show chondral matrix, therefore chondroblastoma was less likely. Taking into account the clinical context, imaging characteristics and size of the lesion, the diagnosis of osteoblastoma was suggested and confirmed later by biopsy.
Osteoblastoma is a solitary, benign bone-forming tumour that occurs in the spine and long bones of young adults. Although the histological characteristics are similar to osteoma, the findings in imaging and clinical behaviour are different. Unlike osteoid osteoma, osteoblastoma is larger than 2 cm in size and patients complain of dull pain that does not worsen at night and does not improve with the intake of NSAID.
In CT spinal osteoblastoma shows an expansile lesion in posterior elements with a mineralised bone matrix and narrow transition zone. MRI features tend to be non-specific and often overestimates the lesion size due to the inflammatory response involving several adjacent bones and the surrounding soft tissues (called the "flare phenomenon”). Depending on the level of matrix mineralisation the signal intensity pattern changes, from a low to isointense signal intensity on T1Wi and from a low to high signal intensity on T2Wi. Intense contrast enhancement with gadolinium is noted given the vascular nature of the tumour. Osteoblastomas can show a type 1 curve of dynamic enhancement, manifested with an early onset of enhancement, a rapid and linear progression of signal intensity and a subsequent gadolinium washout. However, this type of curve is not specific to differentiate between benign and malignant bone tumours. Usually a biopsy is performed to confirm the diagnosis. [2, 3, 4, 5].

Differential Diagnosis List

Final Diagnosis

Spinal osteoblastoma

URL:	https://eurorad.org/case/14834
DOI:	10.1594/EURORAD/CASE.14834
ISSN:	1563-4086