Cuases of MRI negative myelopathies

MRI-negative myelopathies refer to spinal cord dysfunctions where the cause cannot be identified through magnetic resonance imaging (MRI). While MRI is a powerful diagnostic tool, it may not detect certain conditions that can cause myelopathy. Some potential causes of MRI-negative myelopathies include:

1. Vascular disorders: Spinal cord ischemia, arteriovenous malformations, or dural arteriovenous fistulas may not be easily visible on a standard MRI.
2. Inflammatory or autoimmune conditions: Conditions such as neurosarcoidosis, neuromyelitis optica spectrum disorders, or multiple sclerosis might not always show typical lesions on an MRI.
3. Infectious causes: Spinal cord infections, such as viral myelitis, bacterial or fungal infections, may not be easily detected on MRI.
4. Metabolic or nutritional disorders: Vitamin B12 deficiency or copper deficiency can lead to myelopathy, but these may not be visible on MRI.
5. Genetic or hereditary conditions: Conditions like adrenomyeloneuropathy, hereditary spastic paraplegia, or spinocerebellar ataxias may not always be detected through imaging.
6. Functional neurological disorders: These disorders involve abnormal nervous system functioning without visible structural damage, and they can mimic myelopathy.
7. Paraneoplastic syndromes: These rare neurological syndromes can occur as a result of an immune response to cancer and might cause myelopathy without MRI-visible lesions.
8. Transverse myelitis: In the early stages of this inflammatory spinal cord disorder, MRI findings might be inconclusive or negative.
9. Traumatic or mechanical causes: Subtle spinal cord trauma or mechanical compression may not be evident on MRI, particularly if the images are not taken in specific positions.

It is important to note that a negative MRI does not rule out the presence of a myelopathy. If a patient presents with clinical symptoms of myelopathy but has a negative MRI, further investigations and diagnostic tests may be required to identify the underlying cause.

Formation and parts of spinal nerve

The Spinal cord receives information from trunk and limbs and controls the movement of the trunk and limbs. 

It has 31 paired Spinal nerves.

Formation of the spinal nerve 

Two linear series (6 - 8) of nerve fascicles are attached to the dorsolateral and ventrolateral aspects of the cord.The fascicles coalesce to form dorsal and ventral nerve roots.

The roots pass to their corresponding intervertebral foramina, near which they join to form the spinal nerve proper.

Dorsal root

Carry primary afferent neurons from the peripheral sensory receptors to the spinal cord and brain stem. 

Their cell bodies are in the dorsal root ganglia.

Ventral root

Carry : 

1.Efferent neurons (Lower motor neurons), their cell bodies are located in the spinal gray matter. 

2.Preganglionic autonomic neurons

Rami

Spinal Nerves are mixed.They contain both afferent and efferent fibers.

Each spinal nerve is divided into dorsal and ventral rami.

Dorsal ramus: It is thin. supplies muscles and skin of the back.

Ventral ramus:Is larger, supplies muscles and skin of the front of the body and limbs.Connected to the sympathetic chain by the white and grey rami.

Spinal segment and spine of vertebrae

The spinal cord is segmented. 

In the living, the approximate level of the segments is identified by the posterior spinous process of the vertebrae.

Cervical segments : One spine higher than their corresponding vertebrae. C7 segment is adjacent to C6 vertebra.

Thoracic segments : Two spines higher.

Lumbar segments : Three- four spines higher.

Exit of spinal nerves

1-7 spinal nerves : Exit above the upper seven cervical vertebrae.

C8 : Below 7th cervical vertebra.

T1 and the rest of the nerves: Below their corresponding vertebrae.

The Lumbar and Sacral nerves take an oblique course to reach the intervertebral foramina.

The resulting leash of nerve roots forms the Cauda Equina

Anatomy of Spinal cord

Beginning of spinal cord: 

Spinal cord begins at the foramen magnum as a continuation of the medulla Oblongata of the brain.

Shape of spinal cord: It is Cylindrical.

Length of spinal cord: Is about (45) cm.

It occupies upper 2/3 of the vertebral (spinal) canal of the vertebral column.

Levels of termination in different age groups

(1) Up till the 3rd month of fetal life: The spinal cord occupies the entire length of the vertebral canal.

(2) At birth : It terminates at the level of L3.

(3) Children : It ends at the Upper Border of the 3rd Lumbar vertebra.

(4) Adults : It terminates at the intervertebral disc (1st-2nd ) lumbar vertebrae.

Enlargement of spinal cord

Cervical : (C3- T1) Segments for the Brachial Plexus.

Lumbar : (L1- S3) Segments, for the Lumbar and Sacral Plexuses.

Mode of termination of spinal cord

Conus Medullaris : A conical termination caudal to the lumbar enlargement.

Filum terminale : A filament of connective tissue  arises from the tip of the conus. It is attached to the 1st Coccygeal vertebra.