MRI Semeiotics of CIDP
The radiological presentation of chronic inflammatory demyelinating polyneuropathy has distinct patterns. Tomograms clearly visualize significantly thickened nerves. On fat-suppressed (FS) T2-weighted images, the affected nerve fibers appear hyperintense.
Contrast administration demonstrates its diffuse enhancement. This process is well tracked on post-contrast fat-suppressed T1-weighted images. It is important to note that active enhancement involves both intradural and extradural portions of the nerves.
The pathological process also affects the muscular system. Concomitant muscle changes are typical of acute denervation. Marked muscle asymmetry and atrophy are observed. Hyperintense T2 signals and contrast enhancement are recorded in the psoas muscles (psoas) as well as the pelvic musculature.
Differential Diagnosis: Spinal Dural Arteriovenous Fistulas (SDAVFs)
As part of the diagnostic imaging of spinal cord and root lesions, inflammatory changes must be differentiated from vascular pathologies. In dural arteriovenous fistulas, tortuous perimedullary veins are easily visualized after contrast administration. However, normal pial veins may also be dilated in the region of the lumbar enlargement. It is important to remember the strict rule: the distribution of pathologically dilated veins or the level of contrast enhancement are poor landmarks for determining the exact localization of the fistula.
4D dynamic MR angiography is used for the non-invasive search for the shunt. The use of TWIST-type sequences (time-resolved angiography with interleaved stochastic trajectories) helps avoid unnecessary superselective injections during conventional angiography, thereby reducing radiation dose and contrast volume.
Digital subtraction angiography (DSA) remains the gold standard for confirming the diagnosis. Due to delayed venous return, the frame rate should be low (e.g., 1 frame every 2 seconds). The examination is considered negative only if one of the following conditions is met:
- Absolutely all spinal arteries from the foramen magnum to the coccyx are adequately contrasted.
- Veins that appeared pathological on MRI are contrasted and demonstrate normal drainage.
If a fistula is detected, adjacent levels must be contrasted to identify the main radiculomedullary arteries supplying the region.
Treatment Tactics and MRI Follow-up in SDAVFs
The main goal of dural fistula therapy is to halt the progression of the disease. The prognosis depends directly on the severity of symptoms and the stage before treatment initiation.
- Embolization: Possible if it is proven that the target vessel does not supply the spinal cord. The goal of the procedure is complete occlusion of the shunting zone (the most distal part of the artery together with the most proximal part of the draining vein). Incomplete occlusion results in only temporary improvement with a very high recurrence rate.
- Surgical treatment: Early intervention is indicated for incomplete embolization. Any delay in secondary surgery is associated with a poor clinical outcome.
Following successful treatment, abnormalities resolve on MRI, although residual changes may persist for up to 1 year.
Spinal Arteriovenous Malformations (SAVMs)
Unlike SDAVFs, spinal AVMs are supplied directly by spinal arteries (radiculomedullary and/or radiculopial) and are located intramedullary or perimedullary. Drainage occurs through spinal cord veins or perimedullary veins.
Two main subtypes are distinguished:
- Glomerular AVMs (glomerular AVMs / plexiform or nidus type). The most frequent type. This is a tangle of pathological vessels (nidus) located between the feeding artery and the draining vein.
- Fistulous AVMs (fistulous AVMs / intradural AV fistula). Direct arteriovenous shunts, usually located superficially on the spinal cord.
Clinically and radiologically, spinal AVMs have a higher propensity for hemorrhage, which serves as a crucial differential sign on MRI. Symptoms depend on the localization. Like fistulas, they can cause symptoms via venous congestion, while large malformations additionally provoke compressive myelopathy.
Briefly: answers to topical questions
Which nerves and plexuses are most frequently targeted by MRI examination in suspected CIDP?
In suspected CIDP, the targets for MRI examination are most commonly the brachial and lumbosacral plexuses, as well as the spinal nerves and their roots. Tomograms are used to specifically evaluate the following structures:
- Plexus trunks — signal hyperintensity on T2-STIR and DTI sequences, as well as hypertrophy, is revealed.
- Spinal nerves — thickening of the trunks is characteristic.
- Nerve roots — an increase in diameter (greater than 5 mm near the ganglion) and signal hyperintensity on T2-weighted images are noted.
What spinal cord parenchymal changes (aside from vessels) are detected on MRI in spinal dural arteriovenous fistulas?
In spinal dural arteriovenous fistulas, edema may be detected in the spinal cord parenchyma due to increased spinal venous pressure, slowed venous outflow, and venous stasis.
What electroneuromyographic (ENMG) criteria are used to confirm the diagnosis of CIDP?
To confirm the diagnosis of CIDP, ENMG criteria indicating a primarily demyelinating type of peripheral nerve lesion are used. The main electroneuromyographic signs include:
- Decreased conduction velocity — a significant reduction in motor nerve conduction velocity.
- Increased latency — an increase in distal motor latencies and minimum F-wave latencies.
- Conduction blocks — a reduction in the amplitude of the proximal M-response relative to the distal one by 30% or more.
- Temporal dispersion — polyphasia and an increase in the duration of the proximal motor response by 30% or more relative to the distal one.
The "2-second and 1-year" rule for vascular fistulas: during angiography (DSA), the frame rate is slowed down to 1 frame per 2 seconds, and MRI changes after successful treatment can persist for up to 1 year.
Class and exam questions
Can the level of dilated veins on MRI determine the localization of a dural fistula?
No. The distribution of pathologically dilated veins and the level of contrast enhancement are poor landmarks. Additionally, normal pial veins may also be dilated at the level of the lumbar enlargement.
In what case is digital subtraction angiography (DSA) considered completely negative when searching for a fistula?
Only if all spinal arteries from the foramen magnum to the coccyx are adequately contrasted, or if veins suspected on MRI are contrasted and show normal physiological drainage.
How do spinal AVMs fundamentally differ from dural fistulas on MRI?
Spinal AVMs are significantly more prone to hemorrhage, which is a key distinguishing feature. Furthermore, they receive blood supply directly from the spinal arteries and can cause compressive myelopathy.
What else to study on this topic
- Anatomy of intradural and extradural portions of peripheral nerves.
- MRI signs and pathophysiology of acute pelvic muscle denervation.
- Technique of 4D dynamic MR angiography (TWIST) in spinal pathology.
- Superselective injection technique in digital subtraction angiography.
- Mechanisms of compressive myelopathy development in vascular malformations.
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