Elementos de tratamiento

Degenerative Spinal Stenosis

Degenerative spinal stenosis can be central, subarticu-lar (lateral recess) in location (the space between the Symptomatic postoperative epidural hematomas are

very infrequent (occurring in less than 0.2% of surgical pa-tients) and, as with all spinal epidural hemorrhages, are likely due to disruption of the rich venous plexus within the epidural space. Clinical presentation can be within the fi rst 24 hours following surgery or with a several day delay. In young children with high-speed (motor vehicle) craniocer-vical junction injuries, retroclival epidural hematomas can occur, the majority with accompanying tectorial membrane injury. Overt disruption of the tectorial membrane (which is simply a superior extension of the posterior longitudinal ligament), or stretching and detachment can be seen.

Brachial Plexus Injury

The brachial plexus is formed from the anterior nerve roots (ventral rami) of C5–C8 and T1, and innervates the Fig. 3.64 Epidural hematoma, thoracolumbar spine. Sagittal images reveal a fl uid collection (*) anterior to the cord, causing posterior dis-placement and mild compression therein, which extends caudally to the L1–2 level. Superiorly, this extended to the C2–3 level (images not shown). The hematoma is nearly isointense with CSF on the T2-weighted scan, but well seen on the T1-T2-weighted scan due to its inter-mediate signal intensity. The gradual tapering of the fl uid collection in the lumbar region defi nes the fl uid as extradural in location. On the axial T2-weighted scan at the level of the conus, there is a suffi cient diff er-ence in signal intensity between the epidural hematoma and more pos-terior CSF to allow good delineation. There is only mild compression/

deformity of the cord at this level. This epidural hematoma was sponta-neous, with an acute clinical presentation and no known etiology.

Fig. 3.65 Epidural hematoma, cervical spine. A small epidural he-matoma (arrows) is seen both anterior and posterior to the cord, at the level of the foramen magnum, on a midline sagittal image. There is mild posterior displacement of the cord, which is compressed an-teriorly. Note also the extensive abnormal prevertebral soft tissue, representing a combination of hemorrhage and edema.

Fig. 3.66 Retroclival epidural hematoma, tec-torial membrane injury. A moderate in size epidural hematoma is seen just posterior to the clivus, with low signal intensity on T2- and intermediate signal intensity on T1-weighted images, consistent with deoxyhemoglobin (white arrows). CSF fl ow voids make recogni-tion more diffi cult on the axial T2-weighted image. The epidural hemorrhage is also well visualized on sagittal reformatted CT, with high density (black arrow). No overt tear of the tecto-rial membrane is seen. This injury occurs in the pediatric population, with high speed motor ve-hicle accidents the most common cause. In this instance, CT and MR are relatively equivalent for diagnosis of the epidural hematoma, with MR superior for detection of accompanying tecto-rial membrane injury.

Fig. 3.67 Brachial plexus injury, chronic. Sagittal and axial T2-weighted scans demonstrate focal abnormal high sig-nal intensity within the neural foramina on the left at two levels, consistent with CSF. Pseudomeningoceles occur as a result of trauma due to a tear in the meningeal sheath surrounding the nerves, with resultant CSF extravasation.

In this instance there has been bone remodeling (with en-largement of the fl uid spaces) due to the long-standing nature, with the injury having occurred at birth in this 49-year-old patient.

posterior margin of vertebral body and the anterior mar-gin of superior facet, bounded by the thecal sac medially and the pedicle laterally), or foraminal. Degenerative dis-ease anteriorly (a disk bulge with or without accompany-ing osteophyte), posteriorly due to ligamentum fl avum buckling or thickening, and posterolaterally due to facet joint hypertrophy can all contribute to spinal canal steno-sis. In the lumbar spine, it is very common to have all three elements contributing ( Fig. 3.69 ).

The ligamenta fl ava are paired, thick ligaments (pre-dominantly composed of elastic fi bers) that connect the lamina of adjacent vertebral bodies. They extend from the anteroinferior aspect of the superior lamina to the pos-terosuperior aspect of the inferior lamina. The ligamenta

fl ava increase in thickness normally from the cervical to the lumbar regions. They are situated posterolaterally in the canal, and anterolaterally are contiguous with the capsule of the facet joint. In degenerative disease, the liga-mentum fl avum becomes visibly thickened, and thus may cause narrowing of either the lateral recess or spinal canal.

In regard to facet joint hypertrophy, hypertrophy of the superior articular facet is a primary cause of lateral recess stenosis, and resulting nerve compression. Epidural lipo-matosis is simply excessive fat deposition in the epidural space. It is seen in chronic steroid use and in morbid obe-sity, and is usually thoracic and lumbar in distribution. It is reported that patients can become symptomatic, due to compression of the thecal sac.

The neural foramen is bounded by the pedicles superi-orly and inferisuperi-orly, the vertebral body and disk anterisuperi-orly, and the facets posteriorly. Nerve roots exit from the thecal sac, pass through the lateral recess, and enter the neural foramen. Degenerative disease of the disk, endplates, and facets can all contribute to neural foraminal narrowing ( Fig. 3.70 ).

Imaging of the neural foramina, specifi cally for evalu-ation of narrowing, is best performed in the sagittal plane, but more specifi cally in the true cross-section to the foramen. In the lumbar spine, direct sagittal imaging Fig. 3.68 Traumatic brachial plexus injury. This 17-year-old male adolescent presents 5 months following shoulder trauma, with mild dysfunction. A stretch injury is identifi ed on the left, involving the proximal C5 and C6 anterior rami of the brachial plexus, with promi-nence (thickening) and high signal intensity on T2-weighted images due to fl uid and edema. Thick section MIP images are presented, in both the coronal and sagittal oblique planes.

Fig. 3.69 Degenerative spinal stenosis, lumbar spine. At L2–3, the fi rst axial level illustrated, there is mild facet osteoarthritis without signifi cant spinal canal stenosis. At L3–4, the second axial level il-lustrated, there is moderate to severe spinal canal stenosis due to a combination of moderate bilateral facet osteoarthritis, ligamentum fl avum buckling/infolding, and a mild disk osteophyte complex. In regard to the latter, note the much larger diameter of the L3–4 disk as compared to L2–3.

Fig. 3.70 Degenerative neural foraminal narrowing, lumbar spine.

On sagittal imaging at L5–S1, a disk osteophyte complex extends posteriorly and obliterates the inferior portion of the neural fora-men, resulting in compression of the L5 nerve (arrow). Note the lack of normal fat (circumferential to the nerve), which is obliterated in both the anteroposterior or superoinferior dimensions. At L4–5, one level above, a similar process is seen, but less severe with only mild compromise of the neural foramen, with fat preserved both anteri-orly and inferianteri-orly to the nerve.

approximates this plane. However, in the cervical spine, acquisition (or reconstruction) of planes that are oblique in two dimensions are necessary. This is required due to the course of the neural foramina in the cervical spine, which is both anterolateral and superoinferior. Neural foraminal narrowing in the lumbar spine, as viewed on the basis of sagittal MR, is specifi cally assessed by evaluation in both the craniocaudal and AP directions for perineural fat obliteration, and (for the most severe disease) by direct nerve root compression or morphologic change. Evalua-tion of foraminal stenosis should thus include a descrip-tion of the specifi c fat planes that are obliterated, together with any changes in morphology of the nerve itself (due to compression). Although degenerative neural foraminal narrowing is commonly seen in patient exams, the corre-lation between clinical symptomatology and MR imaging appearance is generally poor.

Disk, Endplate, Foraminal, and Spinal Canal Disease

Cervical Spine

The cervical spine is most mobile at C4–5, 5–6, and 6–7, with most disk herniations occurring at these levels. The age of presentation is commonly the third to fourth de-cades. MR is the examination of choice. Thin section axial gradient echo T2-weighted scans are critical for diagno-sis, supplemented by sagittal imaging. A very thin rim of low signal intensity can often be visualized on axial T2-weighted scans along the posterior aspect of the disk (in both normal patients and in the presence of a herniation), corresponding to the dura, volume averaged together with the posterior longitudinal ligament. Thin section

post-contrast axial T1-weighted scans are usually not acquired in patients with radiculopathy; however, these do substantially improve visualization of foraminal disk herniations due to enhancement of the epidural venous plexus. In the cervical spine, the normal epidural venous plexus is prominent, and can be dilated adjacent to a disk herniation. Foraminal disk herniations in particular can be diffi cult to visualize, due to the relative isointensity of the disk to epidural venous plexus on axial gradient echo T2-weighted scans.

Symptoms from an acute cervical disk herniation can be radicular, due to a posterolateral or foraminal location ( Fig. 3.71 ), or myelopathic, with large central herniations.

On high-resolution thin section axial gradient echo T2-weighted scans, the dorsal and ventral nerve roots, as they exit from the cervical cord, can be identifi ed. Paired denticu-late ligaments can also be commonly identifi ed, interposed between the nerve roots. These consist of triangular liga-ment extensions with a broad base along the lateral margin of the cord and their apex attaching laterally to the dura.

As previously discussed, but worth repeating, there are seven cervical vertebrae and eight cervical nerves, C1–C8.

The cervical nerves exit through the foramina above the corresponding numbered vertebrae, with C8 exiting in the foramen below the C7 vertebra. Thus, a posterolateral or foraminal disk herniation at C6–7 will cause compression

of the C7 cervical nerve. Knowledge of the cervical derma-tomes is important for correlation of clinical symptoms with anatomic fi ndings, with pain diagrams distributed commonly to patients prior to the exam in many clinics.

These are also very helpful in the thoracic and lumbar spine. The anatomic distribution of C6, C7, and C8 is easy to remember, with the C7 distribution including the mid-dle fi nger, C6 including the thumb, and C8 including the fourth and fi fth fi ngers.

An acute cervical disk herniation will be visualized as an anterior (or anterolateral or foraminal) epidural soft tissue mass ( Fig. 3.72 ). Close inspection of the cervical foram-ina is mandated, since a disk herniation in this position ( Fig. 3.73 ) is often much less evident than those that are central or paracentral in location. The abnormal soft tis-sue will be contiguous with the disk space, with the only exception being that of a free disk fragment. It should be noted, however, that the majority of free disk fragments will lie immediately adjacent to, and be inseparable from, the native disk. Disk herniations have signal intensity sim-ilar to, on both T1- and T2-weighted scans, the native disk.

The focal nature of a disk herniation is used to diff erentiate this process from a disk bulge, with the latter often defi ned as a process involving 180 degrees or more of the disk cir-cumference. In older patients, and those also involved long term in activities associated with marked motion of the cervical spine, asymptomatic chronic disk herniations are commonly observed ( Fig. 3.74 ).

Although often diffi cult in an individual patient to dif-ferentiate from an acute disk herniation, the presence of associated bony spurs extending from the vertebral body endplates can be used to identify a chronic disk herniation ( Fig. 3.75 ). These bony spurs occur due to bone remodel-ing, with elevation of the periosteum by a disk herniation and subsequent bone deposition. Myelopathic symptoms are more common with chronic disk herniations, with radicular symptoms common in acute disk herniations ( Fig. 3.76 ).

Hypertrophic endplate spurs, also referred to as disk- osteophyte complexes, are commonly seen on both MR and CT, and are typically asymptomatic. Given how frequent these are—most older patients have at least mild multi-level disease—it is not surprising that these do not corre-late well with symptoms. Disk-osteophyte complexes are felt to be the end result of a disk bulge, which is defi ned as circumferential expansion of the disk, specifi cally greater than 180 degrees (and not focal, as with a chronic disk herniation). In many instances the chronic nature of this process can be identifi ed on MR, due to the presence of associated broad based osteophytes (which manifest low signal intensity on all MR sequences) ( Fig. 3.77 ).

These osteophytes are well identifi ed on CT, albeit the associated disk bulge is often poorly visualized. One spe-cial area of note in the cervical spine involves the unco-vertebral joints. These small synovial lined joints (also known as the joints of Luschka) lie between the uncinate Fig. 3.71 Foraminal disk herniation, cervical spine (sagittal plane).

Close inspection of sagittal images can substantially improve detec-tion of foraminal herniadetec-tions, which may otherwise go unrecognized.

A C6–7 disk extrusion, foraminal in location, is easily identifi ed in this patient both on T2- (arrow) and T1-weighted off -midline sag-ittal images. Oblique foraminal views off er a further improvement in depiction and detection of cervical foraminal disease, although unfortunately not performed by most sites.

Fig. 3.72 Central and paracentral disk herniations, cervical spine. Sagittal and axial images reveal presumed acute (recent) disk herniations at C3–4 and C5–6. Note the relative absence of associated osteophytes on the sagittal images. The herniation at C3–4 is central in location, that at C5–6 paracentral with some extension into the foramen on the left. Both disk herniations are likely extrusions on the basis of the sagittal images.

Fig. 3.73 Foraminal disk herniation, cervical spine (axial plane).

Foraminal disk herniations in the cervical spine may be diffi cult to detect, due to isointensity with the venous plexus within the neural foramen on gradient echo T2-weighted scans. Careful image inspec-tion, including all sequences and planes, is mandatory, together with a high sensitivity to abnormal soft tissue (disk material) within the foramen. In this instance, the disk herniation with high signal

intensity (arrow) on the gradient echo T2-weighted scan and inter-mediate signal intensity on the corresponding T1-weighted scan is relatively well visualized. Although seldom used in this application, post-contrast scans allow exquisite visualization of cervical forami-nal disk herniations, which appear as nonenhancing soft tissue easily diff erentiated from the intense enhancement of the abundant ve-nous plexus.

Fig. 3.75 Disk herniation, chronic, cervical spine. The presence of an osteophyte just superior or inferior to a disk herniation, often visual-ized best on sagittal images, implies that the herniation is chronic. On the axial gradient echo T2-weighted scan, at C5–6, a left paracentral and foraminal herniation is visualized with high signal intensity disk material surrounded by a thin low signal intensity rim. This herniation is bordered superiorly by a prominent osteophyte (small black arrow), visualized both on the sagittal FSE T2-weighted scan and—as low signal intensity (white arrow)—on the axial gradient echo T2-weighted scan, covering the high signal intensity disk material immediately below.

Fig. 3.74 Chronic central disk herniation, cervical spine. Asymptom-atic small and large chronic cervical disk herniations are a common fi nding on screening MR examinations. Illustrated is one such small central disk herniation. Without inspection of axial images above and below, or the sagittal images for accompanying osteophytes, it is not possible to confi rm such a herniation as either acute or chronic. There is mild associated cord fl attening. Note that the cen-tral “H” of gray matter is well identifi ed with higher signal intensity than more peripheral white matter on this axial gradient echo T2-weighted scan obtained at 3T.

processes of the lower cervical vertebrae posteriorly and laterally, and allow for fl exion and extension, while limit-ing lateral fl exion. Uncovertebral joints are present from C3 to C7, with encroachment upon the foramina anteri-orly due to degenerative involvement occurring from C2–3 to C6–7. Hypertrophy of the uncovertebral joint is not uncommon in older patients, often asymmetric when comparing side to side and, together with facet osteoar-thritis (posteriorly), causes foraminal narrowing in the AP

dimension ( Fig. 3.78 ). Disk space narrowing is an addi-tional cause of foraminal narrowing, decreasing the height of the neural foramen, with the end result of all these fac-tors being nerve root compression.

Degenerative foraminal narrowing is common in older patients. The bony encroachment of the foramina is well visualized on CT, with sagittal reformatted images impor-tant in this regard. On CT it is readily evident that the os-teophyte commonly extends into the mid-portion of the foramen, dividing the foramen into an upper and lower portion. Keeping this in mind, it is not surprising that, on thin section axial MR images, depiction of the foramen can be limited and misleading. With a large osteophyte lying in the mid-portion of the foramen, unless axial imaging is performed with very thin sections, partial volume imag-ing will lead to poor visualization of the encroachment.

In the cervical spine, the standard MR sequences used for evaluation of the neural foramina include thin section T2*-weighted gradient echo imaging in the axial plane ( Fig. 3.79 ) and fast spin echo T1- and T2-weighted imaging in the sagittal plane. Due to the anterolateral, and slight inferior, course of the neural foramina, oblique sagittal im-ages are, however, best for visualization of the foramina on MR, and should be routinely acquired.

Fig. 3.76 Chronic cervical disk herniation with cord compression and signal abnormality. The chronic herniation seen on FSE (upper) and gradient recalled echo (GRE) (lower) T2-weighted images se-verely narrows the neural foramen on the right. There is moderate narrowing of the foramen on the left, degenerative in nature and un-related to the disk herniation. The cord is deformed (compressed), with focal abnormal high signal intensity (small white arrows) consis-tent with gliosis seen on both scans.

Fig. 3.77 Mild cervical degenerative fi ndings. There is reversal of the normal cervical lordosis. Minimal disk osteophyte complexes are noted at C4–5, C5–6, and C6–7. There is mild to moderate fl at-tening of the cord (versus its normal elliptical appearance in cross-section), at the C4–5 level, a fi nding well seen on axial images.

Fig. 3.78 Uncovertebral hypertrophy. Degeneration of the uncover-tebral joint is common, leading to a broad osteophyte (*) in a char-acteristic position, as illustrated on axial CT. This process can lead both to foraminal narrowing and mild eff acement of the thecal sac, the latter in a paracentral location.

Ossifi cation of the posterior longitudinal ligament is an uncommon cause of acquired cervical spinal steno-sis. There is an increased incidence in Asian patients, in particular Japanese. Other, more common etiologies of cervical spinal stenosis include ligamentous infolding and facet joint hypertrophy. As with all cases of spinal stenosis, patients are at greater risk for traumatic spinal cord injury.

The posterior longitudinal ligament is prominent, with low signal intensity on both T1- and T2-weighted scans ( Fig. 3.80 ), and in some instances with intermediate signal

The posterior longitudinal ligament is prominent, with low signal intensity on both T1- and T2-weighted scans ( Fig. 3.80 ), and in some instances with intermediate signal