Lumbar disc extrusion with a wrapped disc

Findings

There is a left central disc extrusion at L5-S1 that causes mild to moderate left lateral recess narrowing and nerve root displacement without nerve root compression. At this level there is also contrast enhancement traversing the left laminectomy defect and encasing the disc extrusion, consistent with a wrapped disc. There is enhancement in the left lateral recess, suggesting post-operative fibrosis.

Differential diagnosis:
- Wrapped disc
- Peridural fibrosis
- Epidural abscess
- Epidural metastasis
- Nerve sheath tumor
- Disc pseudobulge
- Intervertebral disc protrusion
- Intervertebral disc extrusion
- Recurrent intervertebral disc herniation


Diagnosis: Lumbar disc extrusion with a wrapped disc


Key points: "Wrapped" disc


Disc herniation (protrusion, extrusion, or fragment) may be caused by trauma, repetitive or acute, and are a common source of pain and subsequent back surgery in the general population. In the acute phase, the herniated disc stimulates a fibrovascular response. A "wrapped disc" is the focal herniation (protrusion, extrusion, or fragment) that is encased in vascular scar tissue stimulated by this response and is evident by enhancement on contrast-enhanced T1-weighted images.

Asymptomatic or low back pain and/or radiculopathy are most common in the lumbar spine at L4-L5 and L5-S1. A wrapped disc is a post-surgical sequela, particularly following surgery for spinal stenosis in which the surgical procedure is more extensive, involving a laminectomy and a medial facetectomy.

Best imaging modality: MR (sequences: sagittal and axial T2WI and T1WI, as well as contrast-enhanced axial and sagittal T1WI)
Other imaging modalities: CT, myelography


Imaging findings

MR: Anterior extradural mass contiguous with the disc space extending into the spinal canal
*Contrast-enhanced T1WI: Peripheral enhancement surrounding the disc herniation or fragment with/without central canal, lateral recess, or foraminal stenosis and cord or nerve root impingement. (*most helpful MR sequence)
Non-enhanced T1WI: Isointense to parent disc
T2WI: Iso- to hyper intense to parent disc
General disc hypointensity and height loss at the level of the herniation, as well as postoperative changes (laminectomy defects, etc), degenerative facet disease, and osteophytes, are common associated findings.
CT:
Non-contrast CT: An anterior extradural soft tissue mass that may displace the nerve root / indent the thecal sac
Contrast-enhanced CT: Mild peripheral enhancement of the disc herniation/fragment
Myelography: An extradural mass that indents the thecal sac and nerve root sleeves
Imaging findings of other common differential diagnoses
Peridural fibrosis: Scar within epidural space after lumbar surgery that infiltrates epidural fat, causing homogeneous enhancement that diffusely surrounds the thecal sac and nerve root; increased in T2 signal relative to adjacent disc herniation
Epidural abscess: A distinct fluid collection in the epidural space with peripheral enhancement on post-contrast images, often associated with findings of diskitis
Epidural metastasis: Elongated (cranial-caudal orientation) enhancing mass with osseous involvement and may demonstrate paravertebral extension
Nerve sheath tumor: Avid enhancement surrounding the nerve root, some of which are in a "dumbbell" shape
Disc pseudobulge: Smooth generalized extension of the disc margin without a focal defect due to "uncovering" of disc related to spondylolisthesis
Intervertebral disc protrusion: Anterior extradural mass contiguous with disc space and triangular in shape with broader base than apex; no enhancement
Intervertebral disc extrusion: Anterior extradural mass contiguous with disc space by a "neck," in which this herniated disc material then widens in the epidural space
Recurrent intervertebral disc herniation: Extradural mass contiguous with intervertebral disc margin, demonstrating enhancement peripherally but without central enhancement
Treatment
Conservative: Anti-inflammatory and pain medications, avoid trauma
Surgical: Repeat surgery to remove herniated disc (protrusion, extrusion, fragment)

Sequestered disk

Findings

There is an non- enhancing ovoid mass slightly hyper intense to muscle on both T1 and T2 sequences, in the anterior epidural space at the L3 level, measuring approximatelyl 12 x 8 x 12 mm. This is not contiguous with any adjacent disks. No signal dropout on fat-saturated sequences. The mass causes severe stenosis of the left half of the spinal canal at the L3 level, compressing the left descending nerve roots. T1 and T2 hyper intensity at the endplates abutting L2-L3 disc space representing Modic Type II changes. There is intervertebral disk space height loss at L2-L3 with severe disk desiccation changes.


Differential diagnosis:
- Sequestered disk
- Extruded disk
- Failed back surgery
- Epidermoid
- Epidural abscess
- Epidural hematoma
- Lipoma


Diagnosis: Sequestered disk


A focal disk protrusion is an extension of intervertebral disc material (nucleus pulposus) beyond the vertebral margin (AP diameter < mediolateral diameter). An extruded disk is one in which the nucleus pulposus has herniated through a rent in the annulus fibrosis. The AP diameter > ML diameter, and the disk may migrate craniocaudally, but maintains attachment to the parent disk (frequently symptomatic).
When extruded disk material loses its attachment to the parent disk, it is referred to as a sequestered disk. Sequestered discs usually lodge in the anterior epidural space (AES), just anterior to the posterior longitudinal ligament, and migrate either cephalad or caudad (with equal frequency). Because there is a midline septum associated with the PLL in the AES, the fragment is usually just off midline (to the right or left). Rarely, the sequestered fragment may migrate beyond the PLL into the posterior epidural space, through the dural ( intrathecal location), or into the paraspinal muscles.
They usually resemble the parent disk on MR, with T1 hypo intense and T2 iso- / hypo intense. There may be surrounding T2 hyper intensity and a rim of enhancement from inflammatory changes.
This is a crucial diagnosis to make, as a sequestered disk is a contraindication to limited disk procedures (e.g. Percutaneous discectomy) and may result in failed back surgery.

Hypertrophic olivary degeneration

Findings

Figure 1 and Figure 2: Noncontrast head CT shows acute hemorrhage in the superior and middle cerebellar peduncles.
Figure 3, Figure 4, Figure 6 and Figure 7: FLAIR and T2 show chronic blood products in the superior and middle cerebellar peduncles.
Figure 5 and Figure 8: Axial FLAIR and T2 show T2 prolongation and mild enlargement
of the inferior olivary nucleus of the medulla.


Diagnosis: Hypertrophic olivary degeneration


Hypertrophic olivary degeneration is a unique type of transynaptic degeneration which results in hypertrophy rather than atrophy of the affected structure, the inferior olivary nucleus. The affected circuit involves dentrorubral-olivary connections which were described by Guillain and Mollaret in 1931 as the anatomic connections related to palatal myoclonus, and is commonly referred to as the "Guillain-Mollaret triangle."

The "triangle" consists of 3 nuclei: 1) ipsilateral inferior olivary nucleus (medulla) 2) ipsilateral red nucleus (midbrain) and 3) contralateral dentate nucleus (cerebellum). The ipsilateral red nucleus and contralateral dentate nucleus are connected by the superior cerebellar peduncle. The ipsilateral red nucleus and ipsilateral inferior olivary nucleus are connected by the central tegmental tract. There are no direct anatomic connections between the inferior olivary nucleus and the contralteral dentate nucleus.

Olivary degeneration is typically seen several months after the insult. The side of olivary degeneration depends on the location of original insult and can be predicted by familiarity with the "Guillain-Mollaret triangle." When the primary lesion is in the central tegmental tract, olivary hypertrophy is ipsilateral. When the primary lesion is in the superior cerebellar peduncle or dentate nucleus, the olivary hypertrophy is contralateral. When the primary insult involves both the central tegmental tract and superior cerebellar peduncle, the olivary hypertrophy is bilateral.

The classic clinical finding associated with hypertrophic olivary degeneration is palatal myoclonus, a cyclic jerk of the soft palate.

Creutzfeldt-Jakob Disease (CJD)

Findings

Noncontrasted head CT shows subtle basal ganglia hypo attenuation bilaterally and enlarged bilateral extra-axial fluid spaces. Contrast enhanced brain MR demonstrates increased signal on FLAIR and T2-weighted sequences with corresponding restricted diffusion bilaterally in the caudate nuclei, globi pallidi, posterior thalami, hippocampi and in the cortex of the bilateral occipital-parietal, right frontal and temporal lobes without enhancement. Brain MR 4 weeks later shows persistence of restricted diffusion in the same areas of the brain.

Differential diagnosis:
- Mitochondrial disorder like MELAS or Leigh syndrome
- Creutzfeldt-Jakob Disease
- Viral encephalitis
- Carbon monoxide poisoning


Diagnosis: Creutzfeldt-Jakob disease.


Key points

CJD is one of the neurodegenerative disorders called prion diseases (also known as spongiform encephalopathies), which are uniformly fatal.
90% of cases are sporadic; the other 10% are familial.
CJD is characterized clinically by rapid and progressive dementia, other neurologic abnormalities, and ultimately death.
There is no cure.
WHO criteria for diagnosis requires tissue for definite cases or typical clinical, lab or EEG findings for probable or possible cases; imaging findings are not included.
Typical MR findings of sporadic CJD include increased signal in grey matter on T2-weighted, FLAIR, proton density, and diffusion-weighted (DW) images.
It is more often bilateral.
The caudate nuclei and putamina are usually more affected than the thalami and cerebral cortex.
Diffusion-weighted images are the most sensitive sequence for early, typical signal changes, followed by FLAIR sequences.
Eventually, brain atrophy is a characteristic feature of CJD.
Persistent restricted diffusion, over weeks or months, in typical areas of the brain is virtually diagnostic of CJD.
Acute diffusion restriction in the basal ganglia is seen with carbon monoxide poisoning, but it does not persist and preferentially involves the globus pallidus.

Hallervorden Spatz disease

Findings

Figure 1 : Axial T2 weighted image at the level of the deep gray nuclei demonstrates the classic “eye of the tiger” sign, with T2 prolongation in the medial globi pallidi and hypointensity in the peripheral aspect of the globi pallidi.
Figure 2: Axial SPGR image at the same level demonstrates hypointensity in the globi pallidi as a result of the susceptibility effect from iron deposition.


Diagnosis: Hallervorden Spatz disease


Hallervorden Spatz disease is a rare neurodegenerative condition whose exact pathogenesis is unknown. Abnormal accumulation of iron in the brain, specifically in the globus pallidus and substantia nigra, is felt to play a predominant role in the neurodegeneration caused by the disease. A mutation in the pantothenate kinase gene leads to enzyme deficiency and subsequent accumulation of cysteine and iron chelates. The excess iron is deposited in the basal ganglia and damages neuronal structures.

Symptoms begin early in life, typically in early adolescence, and include extrapyramidal and gait abnormalities. Slow movements, rigid extremities, dystonia, tremors and speech abnormalities are typical findings. No cure exists, and therapy is aimed toward neurological symptoms. The typical clinical course is that of rapid progression, with death in early adulthood in most cases.

Imaging findings are usually classic, and typically described as the “eye-of-the-tiger sign”. This results from symmetric T2 prolongation in the globi pallidi with peripheral hypointensity and hypointensity in the substantia nigra. There is no associated enhancement of the areas of abnormal signal. The neural damage from abnormal iron accumulation results in diminished NAA on spectroscopy. The areas of iron deposition would be more conspicuous on susceptibility weighted images. In cases where the classic history and imaging findings do not lead to the diagnosis, other pathologies that preferentially involve the globi pallidi should be considered. These include metabolic derangements such as methylmalonic acidemia, Kearns-Sayre syndrome, Canavan disease and toxic and ischemic encephalopathies caused by anoxia, carbon monoxide and cyanide poisoning.

Spinal muscular atrophy type I: Werdnig-Hoffmann disease

Findings

Figure 1, Figure 2, Figure 3: There is diffuse cerebral edema with loss of grey-white interface. A "hyperdense" cerebellum and hyperdense MCA vessels are seen. These are, in fact, normal in attenuation, but appear bright when compared with the hypoattenuated adjacent edematous brain.
Figure 4, Figure 5, and Figure 6: MR images demonstrate periventricular cystic spaces and are evidence of remote ischemic changes. There is a subdural fluid collection.


Diagnosis: Spinal muscular atrophy type I: Werdnig-Hoffmann disease


Spinal muscular atrophy (SMA) collectively refers to a family of disorders characterized by progressive degeneration of motor neurons in the spinal cord and brainstem. These disorders are inherited in an autosomal recessive pattern, with deletions or mutations in the survival motor neuron (SMN) gene at the 5q11 locus. Patients present with diffuse symmetric proximal muscle weakness, which is more pronounced in the lower extremities.

In general, there are three recognized types of SMA. These three types are clinically distinguished from one another based upon the age at presentation and the severity of disability. An earlier onset of disease correlates with a worse prognosis, however prognosis is primarily attributed to the severity of muscle weakness.


SMA Type: 1 = Werdnig-Hoffmann Disease

Age at presentation: Preterm – 6 mo
Clinical presentation: Hypotonia, unable to sit without support
Prognosis: Few survive 1 year; death by age 2


SMA Type: 2 = Intermediate type

Age at presentation: 6 mo – 15 mo
Clinical presentation: Proximal weakness; able to sit; unable to stand or walk unaided
Prognosis: Death due to respiratory complications, usually > 2 yo


SMA Type: 3 = Kugelberg-Welander Disease

Age at presentation: 12 mo – adolescence
Clinical presentation: Delayed motor development; able to stand and walk
Prognosis: Death in adulthood


Werdnig-Hoffman disease is both the most severe and the most common form of SMA. Mothers may report decreased fetal movement during the last trimester of pregnancy, and neonates typically present with generalized hypotonia. Involvement of the bulbar muscles leads to difficulty feeding, aspiration, and pneumonia. Involvement of the diaphragm and intercostal muscles leads to progressive respiratory insufficiency. All of these factors result in chronic hypoxia, and eventually death.

The diagnosis of SMA in patients presenting with the appropriate clinical signs and symptoms is confirmed with electromyography, nerve conduction studies, muscle biopsy, and molecular (genetic) analysis. Treatment is primarily supportive.

Hypoxic-ischemic injury to the brain in the term infant is dependent on two factors: the length of the hypoxic episode and the degree of the hypoxia. The damage caused as a result of partial hypoxia differs from that of profound asphyxia.

Chronic respiratory insufficiency in the term neonate will cause neuronal cell death, leading to generalized cerebral cortical atrophy and edema. Central structures (basal ganglia, thalami), and posterior fossa structures, are typically spared.

Total anoxia will lead to hypoxic-ischemic encephalopathy (HIE). In this case, the regions of the brain most affected are those with the highest metabolic demand. This includes the basal ganglia, thalami, hippocampi, brainstem, corticospinal tracts, and sensorimotor cortex.

In an infant with Werdnig-Hoffmann disease, CT scan will reveal:
- Decreased brain tissue attenuation
- Prominent sulci, intrahemispheric fissure, and dilated anterior subarachnoid space

MR is the most sensitive and specific imaging modality in the identification of neonatal hypoxic-ischemic injury. T2-weighted images of the spinal cord in Werdnig-Hoffmann disease will reveal high-signal intensity lesions in the region of the anterior horn secondary to motor neuron loss and associated edema.

Amyotrophic lateral sclerosis (ALS)

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Findings

Figure 1 and Figure 2: Coronal T2-weighted images obtained at the level of the internal capsules. There is continuous linear abnormal high signal intensity within the bilateral hemispheric white matter extending through the corona radiata, posterior limbs of the internal capsules and cerebral peduncles.
Figure 3: Axial FLAIR image at the level of the cerebral hemispheric subcortical white matter. There is bilaterally symmetric high signal intensity abnormality in the white matter fibers of the centrum semiovale.
Figure 4 and Figure 5: Axial FLAIR images at the level of the posterior limbs of the internal capsules. There are bilaterally symmetric, well-circumscribed areas of high signal intensity involving the corticospinal tracts which, at this level, are located in the posterior aspect of the posterior limbs of the internal capsules.
Figure 6: Axial FLAIR image the level of the anterior commisure. Bilateral, well-circumscribed areas of FLAIR high signal intensity localize to the corticospinal tracts are demonstrated.
Figure 7: Axial proton density weighted image at the level of the posterior limbs of the internal capsules. Bilateral, well-circumscribed areas of PD high signal intensity localized to the corticospinal tracts are demonstrated.
Figure 8: Axial proton density weighted image at the level of the cerebral peduncles. There is extension of high signal intensity into the cerebral peduncles along the corticospinal tracts.

The corresponding T1-weighted images demonstrated normal findings. The MRI images of the cervical spine demonstrated normal findings.


Diagnosis: Amyotrophic Lateral Sclerosis (ALS), also known as Lou Gehrig's disease


Amyotrophic lateral sclerosis is a devastating, progressive neurodegenerative disorder that demonstrates both upper and lower motor neuron symptoms. The pathological hallmark of ALS is the degeneration of neurons in the motor cortex and loss of anterior horn cells in the spinal cord with astrocytic gliosis. The surviving motor neurons are shrunken.

Clinically, the symptoms are primarily those of weakness, which may start in the hands or legs or the disease can be manifested by slurred speech and dysphagia. There should be no autonomic, sensory or cognitive involvement.

The exact cause of the disease is not well known. Onset is in the middle and late adult years. About 5-10% of cases are familial. The rest are sporadic. Amyotrophic lateral sclerosis demonstrates a male predilection with a male:female ratio of 1.5:1 5.

Typical MR imaging findings include high signal intensity involving the corticospinal tracts on T2, FLAIR and proton density weighted imaging. This abnormal signal intensity may be seen extending from the hemispheric white matter, through the corona radiata, through the caudal aspect of the posterior limbs of the internal capsules, and finally into the ventral aspect of the brain stem. The signal abnormality appears symmetric and well circumscribed. Occasionally signal abnormality is seen extending into the anterolateral column of the spinal cord. Involvement of the corpus callosum has also been reported.

Care should be taken when evaluating the corticospinal tracts on T2-weighted images because about 50% of normal patients display symmetric foci of high signal intensity that are isointense to gray matter on T2-weighted images within the caudal one-third of the posterior limbs of the internal capsules. However, in normal patients, the signal should never extend above the internal capsule to the corona radiata. Proton density imaging is more specific in evaluating for abnormal signal since in normal patients, the corticospinal tracts are isointense to the remainder of the internal capsule and therefore any abnormal signal on PD should be considered pathological.

The disease is progressive; the mean duration of survival is three to five years.

Positive MR findings correlate with average or rapid progression of the disease, while negative MR findings appear to correlate with slower disease progression.

Olivopontocerebellar degeneration

Findings

Figure 1, Figure 2 and Figure 3: Axial T2 images exhibit reduced brainstem and cerebellar volume, and enlargement of the 4th ventricle and perimesencephalic cistern. Note the normal appearance of the supratentorial brain (Figure 3).
Figure 4 and Figure 5: Sagittal T1 images demonstrate reduced brainstem and cerebellar volume, flattening of the pons, a narrow middle cerebellar peduncle, and enlargement of the 4th ventricle.


Diagnosis: Olivopontocerebellar degeneration


Olivopontocerebellar degeneration (OPCD), once known as Dejerine-Thomas syndrome, is a neurodegenerative disorder caused by progressive infratentorial neuronal loss. The clinical presentation is variable; however, certain features predominate: parkinsonism, pyramidal dysfunction, autonomic dysfunction, and cerebellar ataxia. There is significant overlap with other neurodegenerative disorders including Shy-Drager syndrome, progressive supranuclear palsy, and striatonigral degeneration. These disorders sometimes being referred to as the “Parkinson Plus” syndromes.

Differentiation from Parkinson disease can be extremely difficult with clinical findings alone. It is also important to exclude other causes of progressive neurological decline, such as malignancy, multiple sclerosis, or cerebrovascular disease. Accurate diagnosis is crucial for purposes of patient management, prognosis, and genetic counseling.

The imaging findings of OPCD include pronounced degenerative changes throughout the brainstem and cerebellum as evidenced by flattening of the pons, reduced volume of the medullary olives and middle cerebellar peduncle, and enlargement of CSF spaces including the fourth ventricle and perimesencephalic cistern. This atrophy should be disproportionate to that found throughout the remainder of the brain. Occasionally, demyelination of the transverse pontine fibers may result in a cruciform shaped region of hyperintensity on T2WI, irreverently termed the “Hot Cross Bun” sign.

Evaluation of the middle cerebellar peduncle width is helpful in confirming the diagnosis of OPCD. A measurement of less than 8mm in the sagittal plane has been shown to be both highly sensitive and specific for the disease. Not necessary for diagnosis, but of potential academic interest- these patients will generally demonstrate reduced FDG metabolism on PET and depressed NAA/Cr ratios on MR spectroscopy in the affected areas.

Creutzfeldt-Jakob Disease - Sporadic form

Findings

Figure 1, Figure 2, and Figure 3: T2, DWI, and ADC map show increased signal and restricted diffusion in the basal ganglia. More specifically there is symmetrically increased signal in the caudate and putamen with sparing of the globus pallidus. Additional areas of increased signal are seen in the right and left parietal cortex (Figure 4). No contrast enhancement was seen.


Diagnosis: Creutzfeldt-Jakob Disease - Sporadic form


CJD is a progressive fatal neurodegenerative disorder caused by prion proteins accumulating within the neurons.

There are three forms of CJD. A familial form, a sporadic form, and a variant or iatrogenic. form. The sporadic form (sCJD) is identified in 85% of cases. No genetic or infectious cause can be identified in these patients.

The familial or genetic form (fCJD) is seen in 15% of cases. These cases are identified by DNA analysis of the PRPC gene mutations.

Though it receives the most media attention, the infectious variant or iatrogenic form (vCJD) is the rarest, accounting for 1% of cases.

Diagnosis is based on clinical presentation, EEG findings, and a positive CSF analysis showing 14-3-3 proteins. MRI is reported to have high sensitivity and specificity for the disease with characteristic symmetric signal abnormalities in the basal ganglia and cortical abnormalities. The caudate and putamen are the most frequently involved nuclei. Thalamic involvement is only seen in 14% of patients with the sporadic form. However, thalamic involvement is seen in 78-100% of the variant/iatrogenic forms of CJD. The globus pallidus is usually spared. Diffusion weighted sequences are the most sensitive. Abnormalities are also well seen on T2 and FLAIR weighted sequences. The basal ganglia and cortical lesions show increased signal on T2 and FLAIR with persistent restricted diffusion. The cause of the restricted diffusion is not completely understood.

No treatment is available for the disorder at this time. The clinical course is usually progressive and rapid with most patients expiring within six months to one year from the time of diagnosis.