Difference between hydromyelia and syrindomyelia with mri images

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hydromyelia vs syringomyelia MRI differences imaging

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hydromyelia MRI central canal dilatation vs syringomyelia parenchymal cavity axial image

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Hydromyelia vs. Syringomyelia

Definitions and Core Distinction

Both conditions involve fluid-filled cavities within the spinal cord, but they differ fundamentally in their anatomical location and lining:

Feature	Hydromyelia	Syringomyelia
Definition	Dilatation of the central canal of the spinal cord	Cystic cavity within the cord parenchyma itself
Cavity lining	Lined by ependymal cells (ependyma-lined)	NOT lined by ependyma; surrounded by glial tissue
Location	Strictly within the central canal	Adjacent to/outside the central canal, in white/grey matter
Communication	Communicates with ventricular system/4th ventricle	May or may not communicate with central canal
Fluid content	CSF identical to ventricular CSF	CSF-like fluid; may differ slightly
Cause	Obstruction/increased CSF pressure, often hydrocephalus	Chiari I malformation, trauma, tumors, arachnoiditis
Progression	Often non-progressive ("slit-like," incidental)	Tends to expand and propagate via hydrodynamic forces
Clinical significance	Often benign, may be asymptomatic	Progressive neurological deficits

Pathology

From Robbins & Cotran:

"These disorders are characterized by expansion of the ependymal-lined central canal of the cord (hydromyelia) or by the formation of a fluid-filled cleft-like cavity in the inner portion of the cord (syringomyelia, syrinx) that may extend into the brainstem (syringobulbia)."

From Adams & Victor's Neurology (12th ed.):

Pure hydromyelia = Type IV in classification: developmental dilatation of the central canal, with or without hydrocephalus - non-progressive
Syringomyelia = cavitation of central cord, usually cervical, characterized by dissociated sensory loss (loss of pain/temperature with preserved light touch/vibration/position sense) due to disruption of crossing anterior commissural fibers

When both processes coexist (which is common), the combined term syringohydromyelia or hydrosyringomyelia is used. As the syringomyelic cavity expands, it can compress and obliterate the hydromyelic component, and the connection between the two can be lost.

Classification of Syringomyelia (Adams & Victor)

Type I - With obstruction at foramen magnum + central canal dilatation (developmental): associated with Chiari I malformation or bony foramen magnum anomalies
Type II - Without foramen magnum obstruction (idiopathic developmental)
Type III - With other spinal cord diseases (acquired): spinal tumors, traumatic myelopathy, arachnoiditis, cord compression
Type IV - Pure hydromyelia (developmental), with or without hydrocephalus

MRI Features

Signal Characteristics (both conditions)

T1-weighted: hypointense (dark) - matches CSF signal
T2-weighted: hyperintense (bright) - matches CSF signal
No enhancement on gadolinium contrast (distinguishes from tumor cysts, which may enhance peripherally)
Flow voids may be seen in ~40% of syringes on T2 (pulsatile CSF movement) - associated especially with Chiari malformations

From Grainger & Allison's Diagnostic Radiology:

"Syringomyelia and its cause are well demonstrated by MRI, which shows a well-circumscribed cavity of a similar signal to CSF on T1 and T2 weighted sequences. Pulsatile cysts may show flow-related signal changes."

Distinguishing on MRI - The Core Problem

The honest answer: hydromyelia and syringomyelia cannot be reliably distinguished on MRI in most cases. The Radiopaedia syrinx article states clearly:

"It is very difficult to distinguish the two on imaging. Hence, the collective terms hydrosyringomyelia or syringohydromyelia can also be used."

However, certain imaging features suggest one over the other:

MRI Feature	Hydromyelia	Syringomyelia
Axial location	Central, round/oval, small - in exact midline (central canal position)	Eccentric, larger, may be off-center or multilocular
Size	Small, slit-like or narrow tubular	Often larger, may occupy most of cord diameter
Cord enlargement	Cord usually normal size	Cord enlarged in ~80% of cases
Margins	Smooth, well-defined	Well-defined but may be irregular
Flow voids on T2	Rare	More common (40%), especially with Chiari
Associated findings	Hydrocephalus, myelomeningocele	Chiari malformation, tumor at poles, arachnoiditis
Extent	Usually shorter, may be limited	Often long-segment, multi-level

MRI Images

Figure 1 - Syringomyelia with Chiari malformation (sagittal and brainstem extension)

Syringomyelia MRI - sagittal view showing cord cavity with small size (A) and extension to brainstem (B)

Fig. A (top-left): Sagittal T2 MRI - small syrinx cavity (arrows) in the cervical cord. Fig. B (top-right): Close-up of central cord cavity. Bottom row: Extension into pontomedullary junction (syringobulbia).

Figure 2 - Syringomyelia with Chiari I malformation: cervical to thoracic extent

MRI T2 sagittal and axial views showing large syrinx in Chiari I malformation with cord enlargement

A: Sagittal T2 - large hyperintense fluid cavity (syrinx) running cervicothoracic cord with Chiari I (cerebellar tonsil herniation). B: Axial T2 - round central hyperintense cavity at cervical level. C: Axial T2 at lower level - smaller residual cavity.

Figure 3 - Comparison of different syrinx types (from JCM 2023)

Sagittal T2 MRI comparison: syrinx types A, B, C showing different extents and associations including Chiari and post-traumatic

A: Cervical syrinx with Chiari I (upper arrow = tonsillar herniation, lower arrow = syrinx). B: Long-segment thoracic post-traumatic syrinx (multiple arrows). C: Isolated cervical syrinx with Chiari (arrow at foramen magnum).

Clinical Presentation

Both can present with:

Dissociated sensory loss (cape-like distribution: loss of pain & temperature in upper limbs, preserved vibration/position) - classic for syrinx disrupting anterior commissure
Painless muscle wasting/weakness in the hands and arms (brachial amyotrophy)
Horner syndrome (involvement of sympathetic fibers)
Progressive scoliosis
Spastic paraparesis (if large)
Syringobulbia signs: nystagmus, dysarthria, dysphagia (extension to medulla)

Hydromyelia specifically: often asymptomatic; when an isolated dilated central canal is found incidentally on MRI with no associated Chiari, tethering, or tumor, it is frequently a benign, non-progressive finding.

Key Take-Home Points

Hydromyelia = dilated central canal, ependyma-lined, usually benign
Syringomyelia = parenchymal cavity NOT lined by ependyma, tends to expand, progressive symptoms
They commonly coexist and the combined term syringohydromyelia is used clinically
On MRI both appear CSF-isointense (T1 dark, T2 bright) and cannot be reliably differentiated
MRI focus should be on identifying the underlying cause (Chiari, tumor, arachnoiditis, trauma) rather than trying to distinguish hydro- from syringomyelia
Treatment targets the underlying etiology (foramen magnum decompression for Chiari, tumor removal, shunting)

Sources: - Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 1152 | Adams & Victor's Principles of Neurology, 12th Ed. | Grainger & Allison's Diagnostic Radiology | Radiopaedia - Syrinx | Medscape Imaging Overview

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