Simple oblique lumbar magnetic resonance image technique and its diagnostic value for extraforaminal disc herniation
Dong Hwa Heo, et. al,
Department of Neurosurgery, Chunchon Sacred Heart Hospital,
College of Medicine, Hallyn University,
Chunchon, Korea, and Department of Radiology, Wongu Christian Hospital,
Wongu College of Medicine, Wonsei University, Korea. 
Spine, vol. 34, no. 22, pp. 2419-2423.

The authors reported a prospective study evaluating oblique lumbar magnetic resonance imaging. The authors note that herniated lumbar discs are traditionally diagnosed utilizing conventional lumbar axial and sagittal MRI. However, they state that conventional lumbar MRI might not reveal nerve root compression in the extraforaminal area. Oblique lumbar MRI can provide clear visualization of the dorsal root ganglion and lumbar nerve root in the foraminal and extraforaminal areas.

They reported their results stating that oblique lumbar MRI succeeded in depicting pedicles, dorsal root ganglia, and lumbar nerve roots of the foraminal and extraforaminal areas.  They further noted that in 9 of 10 patients that they studied, nerve root compression by herniated disc in the extraforaminal area was clearly demonstrated when compared with the asymptomatic contralateral side.  They observed that in one patient with scoliosis and spinal stenosis, oblique MRI could not clearly display foraminal or extraforaminal anatomy due to spinal deformity. In light of this data, the authors suggest that oblique MRI can precisely demonstrate nerve roots in foraminal and extraforaminal areas. They describe  the technique as a simple and useful diagnostic tool for extraforaminal lumbar disc herniations.

Extraforaminal disc herniations compress the exiting nerve root rather than the descending nerve root, while centrally herniated discs compress the thecal sac and descending nerve root. Herniated lumbar disc material in the central canal and foraminal area can be easily detected by high resolution CT or conventional axial MRI.  However, they note that extraforaminal herniated discs may not be precisely demonstrated and thus overlooked on conventional axial and sagittal MRI. 

Diverse imaging techniques are employed to diagnose nerve root entrapment in the extraforaminal areas, such as myelography, radiculography, high resolution CT, discal CT, parasagittal MRI, MR neurography and 3-dimensional MR imaging. However, the authors point out that some imaging methods might not precisely demonstrate foraminal and extraforaminal anatomy, leading to difficulty in interpretation. Invasiveness is another disadvantage of certain methods.

They explain that selective lumbar radiculography is useful  for detecting lesions in the intra- and extraforaminal zones and during this procedure local anesthetic and contrast medium are injected to the nerve roots. Therefore, only diagnostic images but diagnostic pain alleviation can be evaluated.  Although this technique is a useful diagnostic tool for extraforaminal disc herniations, invasiveness is a disadvantage. 

With respect to MR neurography, this is a nerve-based fast spin echo imaging and can detect foraminal and extraforaminal nerve roots.  To obtain optimal images, MR neurography has been performed at nerve-oriented planes and for this technique to be included in routine MRI lumbar examinations, more clinical trials would be required. 

They note that parasagittal MR imaging has frequently been used to diagnose entrapment of the lumbar nerve roots and is a technique that most clinicians are familiar with.  Parasagittal images can easily be taken during conventional sagittal MRI. Narrowing or obliteration of the neural foramen is expected to result in entrapment of nerve roots. Extraforaminal disc herniation can be diagnosed by parasagittal MRI correlated with axial images. However, these images do not precisely demonstrate the foraminal or extraforaminal anatomic structures. 

They describe gadolinium enhanced fast low-angle shot 3-dimensional MRI, which can demonstrate the nerve root sleeve and nerve root ganglion.  They agree that this technique can successfully diagnose pathologic extraforaminal lesions. However, two advantages of the procedure that they describe, a turbo-spin echo oblique MRI, is that it does not require gadolinium enhancement and it is more familiar to clinicians and thus easier to interpret. 

The authors describe the anatomy, noting the lumbar spinal nerve roots pass obliquely through the intervertebral foramen in an  inferior-central direction and therefore axial, sagittal, and coronal MRI scans do not precisely demonstrate spinal nerve root in the extraforaminal area.  Oblique lumbar MRIs are taken using the anatomic features of spinal nerve roots. They suggest that oblique images can demonstrate the extraforaminal region and its exiting nerve roots more accurately than axial sagittal  coronal planes. 

Descending nerve root compression in the foraminal area is easily visible on oblique imaging. In the case of a right-sided foraminal disc herniation with upward migration at L4-5, an oblique MRI was able to demonstrate the right exiting nerve root and descending nerve root, revealing that both of these nerve roots were  affected by the herniated disc.  In a case they describe in which they found that both the L4 and L4-5 nerve roots were affected by delineated discs, utilizing this oblique technique, they performed a right-sided L4 hemilaminectomy and completely removed the disc particle that had migrated upward, decompressing both the right L4-5 and nerve roots. 

They state that they can also detect conjoint nerve roots with respect to this method. 

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Classification, Differential Diagnosis and Spectrum of Disease
Gebauer, Farjoodi et al
J Bone Joint Surg Am 2008; Suppl4:146-62

The authors note that magnetic resonance imaging is an excellent modality for imaging pathologic processes involving the spine.  It permits high resolution imaging of not only the osseous structures but also the soft tissue structures in multiple orthogonal planes through the use of varying pulse sequences that allow for characterization of the different tissues in and around the spine.  the purposes of this report were designed to describe the specialized pulse sequence and imaging techniques available for evaluation of the spine, described the defining characteristics of the three compartments into which spinal tumors could be classified to define the differential diagnosis for tumors identified in each of these three compartments, in addition to providing a base knowledge of the tumors that are commonly encountered in the spine. 

The authors proceeded to discuss the basic pulse sequences for MRI imaging of the spine.  They also describe tissue characteristics on magnetic resonance imaging. 

A discussion followed regarding differential diagnosis of spinal tumors by compartment.  They stated that in the extradural compartment, the benign tumors that one might expect to see include osteoblastoma, osteochondroma, eosinophilic granuloma, lipoma, giant cell tumor, osteoid osteoma, aneurysmal bone cyst and hemangioma. They stated that in the extradural compartment, the malignant tumors one might expect to find would include metastatic disease, myeloma, lymphoma, osteosarcoma, Ewing sarcoma, neuroectodermal tumor, chordoma and chondrosarcoma. 

They then discussed the intradural-extramedullary compartment in which one might find nerve sheath tumors such as Schwannoma or neurofibroma, meningioma, lipoma, subarachnoid seeding (metastatic disease), epidermoid lesion and dermoid.  They stated that in the intramedullary compartment one can find an apendymona, astrocytoma, hemangioblastoma, paraglioma, and metastatic disease.  The authors discussed in detail each of the types and classifications of tumors in this extremely well-written paper.  They concluded that an understanding of the MRI characteristics of spinal tumors is an essential component of the evaluation in a patient with spinal abnormalities.  Determining the compartmental location of the lesion and taking into account additional information from other imaging modalities and patient specific factors such as age and medical history, the surgeon can develop a differential diagnosis for the tumor type.  Additional evaluation of the magnetic resonance imaging characteristics including tissue composition and contrast enhancement may provide a definitive diagnosis for some tumors therefore allow for determination of patient prognosis and the need for adjuvant therapy.  They state that in addition by defining the compartment in which the tumor resides and its relation to the neighboring anatomic structures, the spine surgeon can select the appropriate operative approach for biopsy or resection or both of the tumor.  By visualizing and understanding the anatomic limits of the tumor before proceeding to the operating room, a more specific and effective operation can be planned.