Non-Tumoural Spinal Cord Lesions

Multiple Sclerosis

Multiple sclerosis (MS) is a progressive neurodegenerative disorder characterised by multiple inflammatory demyelinating foci called ‘plaques’. The spinal cord is commonly involved with changes on autopsy in up to 98% of the cases. One-third of MS patients will have isolated spinal cord involvement. Spinal cord abnormalities in MS include focal lesions, diffuse involvement, axonal loss and spinal cord atrophy. Focal MS lesions appear as oval- or wedge-shaped T ₂ -hyperintensities located preferentially in the lateral and posterior parts of the spinal cord, which may or may not be swollen. Lesion enhancement is seen less frequently than in the brain, and is commonly subtle. Ring-like or intense nodular enhancement may also occur ( Fig. 50.1 ).

Diffuse signal intensity abnormalities extending over multiple vertebral segments resembling transverse myelitis (TM) are seen in primary and secondary progressive MS. Spinal cord atrophy is associated with clinical disability, and is more common in the upper part of the spinal cord.

Tumefactive MS lesions can sometimes present a diagnostic challenge, with a clinical presentation and imaging features mimicking tumours. Magnetic resonance imaging (MRI) appearances are classically of large (>2  cm) circumscribed lesions with little mass effect or oedema. They are typically found in the supratentorial white matter (WM) but can also involve grey matter and the spinal cord ( Fig. 50.2 ). Approximately half of tumefactive lesions enhance with a typical open-ring pattern, with the incomplete portion of the ring on the grey matter side of the lesion. Corticosteroid therapy leads to a dramatic reduction in the size of the lesions.

Acute Disseminated Encephalomyelitis

Acute disseminated encephalomyelitis (ADEM) is an inflammatory demyelinating central nervous system (CNS) disease of the brain and spinal cord, with a distinct tendency to a perivenous localisation of pathological changes. ADEM develops mostly 1 or 2 weeks following a viral disease or prior vaccinations. Cerebrospinal fluid (CSF) analysis shows a high protein level. A high serum titre of immunoglobulin G (IgG) specific for myelin oligodendrocyte glycoprotein (MOG) has been described in almost one-half of the studied cases of ADEM.

The spinal cord is involved in 30%–40% of the cases. On MRI, non-enhancing or minimally enhancing hyperintense lesions are seen in the spinal cord on long repetition time (TR) sequences. Skip lesions, as well as long segment hyperintensity, may be detected ( Fig. 50.3 ). Complete resolution of abnormalities will usually be seen on follow-up images.

Acute Transverse Myelitis

Acute transverse myelitis (ATM) is a heterogeneous syndrome with acute or subacute onset, manifesting as weakness, sensory loss and autonomic dysfunction. It is associated with infectious or systemic autoimmune diseases, but in most cases the aetiology remains unknown (idiopathic).

The outcome of ATM ranges from full recovery to complete inability to walk or even death from respiratory failure. On MRI, usually long intramedullary T ₂ high signal intensity with cord swelling will be seen. Enhancement may be present. In comparison with spinal cord involvement in MS where focal lesions do not take more than half of the cross-sectional area of the cord, lesions in TM tend to involve more than two-thirds of the cross-sectional area of the cord ( Fig. 50.4 ).

Depending on the length of the signal abnormality, TM can be divided into longitudinally extensive TM (LETM), when signal abnormalities extend more than two segments, and acute partial TM (APTM), when signal abnormalities extend less than two vertebral segments.

Neuromyelitis Optica

Neuromyelitis optica (NMO) is considered to be an autoimmune antibody-mediated disease, induced by a specific serum autoantibody, the NMO-IgG, directed against aquaporin-4. Antibodies to aquaporin-4 (AQP4-Ab or NMO-IgG) are sensitive and highly specific serum markers of NMO. NMO affects all ages, including children and the elderly. It has a relapsing course in 80% of the cases and women are more commonly affected. The disease was initially considered a disorder affecting predominantly spinal cord and optic nerves; however, brain is also commonly involved.

In acute optic neuritis, MRI shows a non-specific optic nerve sheath thickening, T ₂ -hyperintensity of the optic nerves with swelling and enhancement. On follow-up images optic nerve atrophy and residual hyperintensity may be seen ( Fig. 50.5 ).

Spinal cord involvement manifests itself as LETM with intramedullary T ₂ high signal extending more than three vertebral segments. In up to 90% enhancement will be present. In the cervical spinal cord, an irregular ring-like enhancement pattern has been described (‘shaggy ring enhancement’) and will be present in 30% of patients (see Fig. 50.5 ). On axial T ₂ weighted MRI NMO lesion demonstrate high signal named ‘bright spotty lesions’, which is considered a valuable discriminating factor between NMO and MS. On follow-up magnetic resonance (MR) defects, atrophy and central cavities, have been described.

Brain abnormalities have been described in up to 40%–60% of NMO patients and they include: non-specific supratentorial WM lesions, diencephalic lesions surrounding third ventricles and cerebral aqueduct, dorsal brainstem lesions adjacent to the fourth ventricle (area postrema), unilateral or bilateral corticospinal tract lesions, hemispheric WM lesions and lesions surrounding lateral ventricles.

Periventricular signal intensity abnormalities (around the third and fourth ventricle, and in the periaqueductal region) can be detected on MRI, corresponding to brain areas with the highest aquaporin concentrations (see Fig. 50.5 ). Enhancement on brain MRI is not common (13%–36%), with ‘cloud-like enhancement’, which appears as multiple patches of enhancing lesions, being the most common type.

NMO has been associated with other autoimmune diseases, including hypothyroidism, Sjögren syndrome (SS), systemic lupus erythematosus (SLE), pernicious anaemia, ulcerative colitis, primary sclerosing cholangitis, rheumatoid arthritis, mixed connective tissue disorders and idiopathic thrombocytopenic purpura.

Systemic Lupus Erythematosus

SLE is a relapsing and remitting, chronic, multisystem autoimmune disease. Although the frequency of neuropsychiatric lupus has been reported as high as 95%, SLE-related myelopathy is rare, with prevalence varying between 1% and 2%. It is, however, often associated with high morbidity and mortality and is frequently recurrent. Because of this importance, SLE myelopathy has been included in the new classification criteria for SLE. Involvement of the spinal cord in SLE usually occurs during a time of acute exacerbation and is occasionally the first manifestation of SLE in an undiagnosed patient.

SLE myelopathy manifests mostly as an LETM. The pathophysiological mechanism of TM in SLE is uncertain, although vasculitis and arterial thrombosis resulting in ischaemic cord necrosis, have been suggested. Studies have suggested a higher incidence of antiphospholipid and NMO IgG antibodies in those with SLE myelopathy than in the general SLE population and this has contributed to our understanding of the disease process.

The high to mid-thoracic cord is most commonly affected, resulting in a sensory level and frequently in paraplegia, which may be complete. Cervical myelopathy and cauda equina involvement, on the other hand, often cause only partial motor and sensory loss. MRI demonstrates T ₂ hyperintensity and oedema, frequently with spinal cord expansion. Lesions may demonstrate patchy enhancement during the acute phase ( Fig. 50.6 ). MRI may be normal in the early stages, in which case a contrast-enhanced MRI should be repeated 2 to 7 days after the initial manifestation. Improvement or resolution of findings correlates with clinical improvement. Indeed, some patients may have a normal MRI if they have already received treatment.

Sarcoidosis

Sarcoidosis is a systemic condition of unknown aetiology characterised histologically by non-caseating granulomatosis. Although CNS sarcoidosis is found in approximately 25% of cases on post-mortem examination, symptomatic involvement in life is uncommon. Isolated neurosarcoidosis of the spinal cord is extremely rare. Clinical presentation depends on the site of involvement and is often non-specific. Neurosarcoidosis of the spinal cord presents either as focal lesions or as long T ₂ hyperintensity with fusiform cord enlargement ( Fig. 50.7 ).

Focal enhancing lesions are associated with recent neurological impairment and usually respond to corticosteroid treatment. Non-enhancing lesions resembling those seen in MS are irreversible, associated with chronic neurological impairment, and likely correspond to sequelae of previous inflammatory lesion.

The enhancement characteristics can be helpful, especially in differentiating it from other causes of TM such as NMO. The enhancement pattern in spinal cord sarcoidosis is more likely to be linear and subpial rather than the patchy incomplete ring of enhancement associated with NMO (see Fig. 50.7 ). Typically, dorsal subpial linear enhancement will be detected on sagittal post-contrast images. On axial post-contrast images a ‘trident pattern’ due to the enhancement of the central canal has been described. A ventral subpial enhancement (a ‘braid-like sign’) has also been reported.

Furthermore, persistent contrast enhancement for 3 months following steroid treatment is more likely seen in sarcoidosis than in other causes of TM. The diagnosis of CNS sarcoidosis can represent a challenge on spinal cord imaging alone and is supported by the presence of typical appearances of brain sarcoidosis, such as involvement of the hypothalamic–pituitary axis, leptomeningeal enhancement or dural masses, as well as other diagnostic tests, such as elevated serum angiotensin-converting enzyme (ACE) levels, positive Kviem test and typical computed tomography (CT) chest or positron emission tomography (PET)/CT findings.

Guillain–Barré Syndrome

Guillain–Barré syndrome is an acute immune-mediated polyneuropathy. Affected individuals have a typical areflexia and ascending paralysis type of symmetrical weakness, with or without sensory loss, which starts in the feet and hands and progressively moves up the limbs to the trunk over a few days. The trigger is frequently a viral illness with the production of antibodies that cross-react with myelin in the peripheral nervous system. Approximately 80% make complete or near-complete recovery over a few weeks from onset, with approximately 10% developing persistent symptoms that may have a relapsing and remitting course. In approximately 10% of cases, it can be life threatening if the respiratory muscles are affected.

Diagnosis is usually clinical and supplemented by nerve conduction studies and CSF examination. MRI demonstrates nerve thickening and enhancement, which is non-specific and is seen in other inflammatory disorders but is a useful diagnostic adjunct.

Chronic Inflammatory Demyelinating Polyneuropathy

Chronic inflammatory demyelinating polyneuropathy (CIDP) is an immune-mediated chronically progressive or relapsing symmetric sensorimotor disorder. It can be considered the chronic equivalent of acute inflammatory demyelinating polyneuropathy, the most common form of Guillain–Barré syndrome. Contrary to Guillain–Barré syndrome, CIDP has an insidious onset and evolves in either a slowly progressive or a relapsing manner. Preceding infection is infrequent. As with Guillain–Barré syndrome, the mainstay of treatment is immunosuppressive or immunomodulatory intervention. MRI findings are similar, with enhancing thickened nerve roots. Acute and subacute muscle denervation is demonstrated by hyperintensity within the affected muscle on fluid-sensitive sequences, such as T ₂ weighted or short tau inversion recovery (STIR) images. In chronic denervation, muscle atrophy and fatty infiltration demonstrate high signal changes on T ₁ weighted sequences in association with volume loss. CIDP may therefore show both these changes, depending on the stage of imaging ( Fig. 50.8 ).

Spinal Dural Arteriovenous Fistula

Over 80% of spinal arteriovenous malformations (SAVMs) represent spinal dural arteriovenous fistulas (SDAVFs) located in the spinal dural mater, usually close to a root sleeve. Such fistulas are most commonly located in the thoracolumbar region. They can, however, occur at any level, though in the cervical spine only around the foramen magnum, except in extremely rare cases. The fistula is usually supplied by one or two branches of a nearby radiculomeningeal artery and shunts often via a single vein into intradural radicular veins. The increase in spinal venous pressure results in slow venous drainage and stagnation, because radicular veins and intramedullary veins share a common venous outflow, leading to chronic venous congestion, cord oedema and eventual ischaemia. This results in the clinical findings of progressive myelopathy. SDAVFs are more common in middle-aged to elderly men and the typical presentation is of a slowly progressive gait disturbance, difficulty climbing stairs and paraesthesia. Bowel and bladder incontinence, erectile dysfunction and urinary retention are often seen late in the course of the disease but may be the presenting feature. The condition is often misdiagnosed clinically as the non-specific and insidious presentation mimics other more prevalent conditions such as spinal stenosis, tumours and myelopathy.

On MRI an ill-defined central intramedullary hyperintensity extending over multiple levels with associated cord expansion will be recognised. Engorged perimedullary veins can be seen as flow voids, which are more pronounced on the dorsal surface compared with the ventral surface. Although these are readily depicted on standard T ₂ sequences, they become much more conspicuous on heavily T ₂ weighted sequences (constructive interference in steady state (CISS), fast imaging employing steady-state acquisition (FIESTA) or 3D turbo spin-echo (3D TSE)) ( Fig. 50.9 ). A hypointense rim may also be seen, most likely because of deoxygenated blood within dilated capillary vessels surrounding the congested oedema. On post-contrast images in up to 80% of cases diffuse enhancement of the cord with non-enhancing parts (‘missing-piecesign’) will be observed.

The coiled perimedullary veins are easily depicted following contrast enhancement. It should be noted that normal pial veins can be prominent at the level of the lumbar enlargement of the spinal cord and that the distribution of abnormally enlarged veins, or the level of the enhancement when present, are poor guides to the location of a dural fistula. The site of the fistula can sometimes be shown by dynamic contrast-enhanced magnetic resonance angiography (MRA). Multiplanar reformats of 4D dynamic MRA sequences, such as time-resolved angiography with interleaved stochastic trajectories (TWIST), can show non-invasively the site of the SDAVF in cases where the diagnosis is uncertain and can guide digital subtraction angiography (DSA), helping to avoid unnecessary superselective injections of all possible arterial feeders, reducing the radiation dose and contrast administered during DSA (see Fig. 50.9 ).

DSA is indicated to confirm the diagnosis. When searching for a dural fistula, imaging rate should be slow, say one frame every 2 seconds, because of delayed venous return. A large number of arteries may have to be injected before the lesion is found. The study should not be regarded as negative unless (A) all the spinal arteries from the foramen magnum to the coccyx have been opacified adequately or (B) the veins thought to be abnormal have been opacified and shown to drain normally. If a lesion is found, adjacent levels should also be injected and the major radiculomedullary arteries supplying the region must be identified.

Treatment aims to stop disease progression, with prognosis dependent on the symptoms and stage of disease pre-treatment. Embolisation of arteries supplying a dural fistula may be feasible, provided the vessel to be embolised can also be shown not to supply the spinal cord. The aim of treatment is to exclude the shunting zone (i.e. the most distal part of the artery together with the most proximal part of the draining vein). In cases of incomplete occlusion, a transient improvement of symptoms will occur, with high rate of recurrence. Early surgical intervention should be considered for incomplete embolisation, as delay of secondary intervention is associated with a poor outcome. Following successful treatment, resolution of MR abnormalities will follow; however, abnormalities can persist for up to 1 year.