The spectrum of radiating and non-radiating low back pain is a common annoying clinical problem. The majority of cases are attributed to discogenic lumbar nerve root compression, for which MRI is primarily used for evaluation [8,9,10]. It is not uncommon to encounter normal routine protocol MRI while a patient is still suffering from pain. Literature includes reports for many cases whose pain were attributed to sacro-iliac, gynecological, and other pelvic pathologies [2,3,4, 6, 11,12,13]. Others described nerve entrapment syndromes by muscles and tendons, as pyriformis syndrome [14,15,16].
In MR imaging, STIR is recognized as a beneficial sequence of high sensitivity in detection of bone as well as soft tissue pathologies through the illumination of high water content pathologies against suppressed background fat signal. It allows homogeneous fat suppression, insensitive to field heterogeneity and applicable in low as well as high magnetic strength scanners [17,18,19,20].
The MR neurography imaging of lumbosacral plexus has also utilized STIR besides T1 sequences in axial and coronal planes; and the revolutionized MR neurography techniques in the era of 3-Tesla MRI scanners introduced high-resolution images of the nerve plexus through three dimensional (3D) isotropic acquisition imaging with the advantage of maximum intensity projection (MIP) as well as curvilinear reconstructed images. High-resolution images allow detection of signal changes along the nerves and small neuromas and may help to point to sites of entrapment [21,22,23,24,25]. While MR neurography provides visual analysis of the nerves, diffusion-weighted imaging can provide further quantitative assessment through measurement of the apparent diffusion coefficient value (ADC) and fraction anisotropy (FA) of entrapped nerves and nerve roots and using ADC values for differentiating benign from malignant neurogenic tumors [26,27,28,29,30]. Diffusion tensor imaging (DTI) and tractography can also be implemented to trace the neural tracts .
However, a standard coronal STIR sequence, covering the para-spinal and pelvic region, can be looked at as a primary problem solving method through detection of gross abnormalities overlooked on routine MRI protocol in extra-spinal sciatica. It is less demanding technically and available through scanners of different magnet strength making it a simple adjustment to routine imaging protocol.
In the current study, routine MR protocol images resulted in categorization of 21% of the included patients as normal while after adding coronal STIR images, 13% were categorized as normal; a discrepancy explained by the fact that 44 patients had extra-spinal abnormalities that were overlooked using the routine MR protocol images alone while detected on the additional coronal STIR images. A wide range of extra-spinal abnormalities were detected. Gynecological abnormalities (ovarian cysts and uterine fibroids) constituted half of these patients; however, the relation to the patients’ presenting symptoms was considered equivocal. In 15 patients (6.9%), we were confident that the extra-spinal abnormalities could explain pain and influenced the treatment plan, with absent nerve root impingement on routine protocol images in 12 of them.
In a study by Gleeson and his colleagues , additional coronal STIR images altered the diagnosis in 2.4% of the studied patients; which is much less than the reported percentage in our study. This can be explained that coronal images field of view in their study was limited to the sacrum and sacroiliac joints; while in our study, the FOV was extended down to the lesser trochanters of the femora allowing the detection of abnormalities within the pelvis and hips. In other studies, reported a percentage close to that in our study, 6.8% by Gupta and his colleagues and 5.7% by Laporte and his colleagues [4, 6].
Statistical analysis in our study aimed to identify the factors to which coronal STIR sequence has additional value and relevant application. It yielded significant correlation between the presence of extra-spinal cause of sciatica and positive history of trauma and neoplasm, normal routine protocol images, and absent nerve root impingement on routine protocol images. Extra-spinal sciatica was more prevalent in the age groups ranging from 20 to 39 years, being of significance in the age group: 20–29 years. In their study, Laporte et al. reported significant association between extra-spinal cause of pain and absent disco-radicular impingement on routine images .
The main limitation of the study is that we could not follow the patients diagnosed having gynecological abnormalities to correlate the presence of such abnormalities to the patients’ pain, worth to mention that they constituted half of the detected extra-spinal abnormalities and have been reported in various case reports as unusual causes of sciatica. Yet additional coronal STIR images could detect the presence of gynecological and other pelvic abnormalities which may be referred to for consideration by the clinician in otherwise normal routine images protocol.