An assessment of fluid-fluid levels on magnetic resonance imaging of spinal tumours.

To assess the degree of fluid-fluid levels on MRI in spinal tumours compared with final diagnosis, and the outcome of needle biopsy in such cases. Retrospective review of patients with a spinal tumour that contained fluid-fluid levels. Data collected included age, sex, spinal location, and final diagnosis. The outcome of needle biopsy was investigated. Forty-two patients were included (19 males; 24 females; mean age 27.5 years, range 5-80 years), the commonest diagnoses being aneurysmal bone cyst (n = 25; 59.5%) and metastasis (n = 5; 11.9%). All patients with a malignant diagnosis were > 50 years of age apart from 2 who had metastases from a known primary cancer, while all patients apart from 1 with aneurysmal bone cyst were < 35 years of age. Needle biopsy was undertaken in 29 cases (69%) and diagnostic in 18 (62%). Patients with FFL occupying > 2/3 of the lesion were significantly more likely to have an aneurysmal bone cyst (p = 0.008) while those with FFL occupying < 2/3 of the lesion were more likely to have a malignant tumour (p = 0.001). The sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of > 2/3 FFLs occupying the lesion were 97.1%, 75%, 94.3%, 85.7%, and 92.9% respectively for differentiating a benign from a malignant spinal tumour. Children and younger adults with spinal lesions containing > 2/3 FFLs were very unlikely to have malignancy. However, in patients > 50 years of age or those with lesions containing < 2/3 FFLs, a malignant lesion is much more likely.