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Myelography

Myelography is a diagnostic imaging procedure that involves the injection of a contrast agent into the subarachnoid space surrounding the spinal cord, followed by the use of fluoroscopy or computed tomography (CT) to produce detailed images of the spinal cord, nerve roots, and meninges.^[1] This technique allows for the evaluation of abnormalities such as herniated discs, spinal stenosis, tumors, infections, and nerve compressions that may not be fully assessed by standard X-rays or when magnetic resonance imaging (MRI) is contraindicated or inconclusive.^[1] The concept of myelography was first proposed in 1919 by neurosurgeon Walter Dandy using air as a contrast medium,^[2] though Jean-Athanase Sicard and Jacques Forestier described the modern oil-based method in 1921.^[3] Originally a primary spinal diagnostic tool, myelography has declined with the rise of MRI in the mid-1980s but remains relevant for specific cases like CSF leak detection, brachial plexus avulsions, and postoperative evaluations where MRI is limited (e.g., by artifacts or contraindications).^[3] Recent advancements, such as dynamic CT myelography as of 2025, have improved its precision for CSF leak localization.^[4] It offers benefits including high accuracy for nerve root issues—CT myelography shows up to 100% sensitivity for root avulsions in recent studies, often superior to MRI in challenging cases—and utility in patients with pacemakers or claustrophobia.^[3]^[5] However, risks include common post-procedure headaches from CSF leakage (up to one-third of cases),^[6] rare allergic reactions to contrast (less than 1%), infection, bleeding, or nerve injury.^[1]^[7] Overall, it serves as a safe, targeted tool in multimodal imaging approaches.^[1]

Overview

Definition and Purpose

Myelography is a diagnostic imaging procedure that involves the intrathecal injection of a contrast medium into the subarachnoid space, followed by radiographic imaging using X-rays, fluoroscopy, or computed tomography (CT) to visualize the spinal cord, nerve roots, and surrounding structures.^[8] This technique provides detailed images of the spinal canal by outlining the flow of cerebrospinal fluid (CSF) and highlighting any disruptions or abnormalities within the thecal sac.^[1] The procedure targets key anatomical components, including the spinal cord, cauda equina, exiting nerve roots, and the subarachnoid space, enabling precise evaluation of their integrity and relationships to adjacent tissues.^[9] The primary purpose of myelography is to identify and characterize spinal pathologies that may not be fully discernible with non-invasive imaging modalities like MRI, particularly in cases involving hardware artifacts or contraindications to magnetic fields.^[1] It is employed to detect conditions such as spinal cord compression, nerve root impingement, tumors, herniated discs, infections, trauma-related injuries, arachnoiditis, and CSF leaks, aiding in treatment planning and surgical decision-making.^[8] For instance, it excels in delineating the extent of disc herniations or stenotic changes that compress neural elements, providing critical information for interventions like decompression surgery.^[9] Originating in the early 20th century, myelography has evolved from rudimentary contrast techniques to a sophisticated adjunctive tool integrated with modern CT and fluoroscopic systems, enhancing its diagnostic accuracy while minimizing risks associated with earlier agents.^[3] Today, it remains valuable for complex cases where high-resolution visualization of dynamic CSF flow and neural anatomy is essential.^[10]

Historical Development

The concept of myelography was first proposed in 1919 by American neurosurgeon Walter Dandy, who suggested intrathecal injection of an opaque substance to visualize the spinal subarachnoid space, initially using air as a contrast agent in a technique akin to pneumoencephalography.^[11] However, air myelography proved risky due to complications like severe headaches and meningeal irritation from gas introduction.^[12] In 1921, French physicians Jean-Athanase Sicard and Jacques Forestier introduced the first practical myelographic method by injecting Lipiodol, an iodized poppy seed oil, into the subarachnoid space, enabling radiographic visualization of spinal cord abnormalities such as tumors.^[3] During the 1920s and 1930s, Lipiodol gained widespread use but was criticized for its viscosity, which hindered complete removal and led to chronic irritation.^[13] By the 1940s, a shift occurred from air and early oil-based agents to improved oil contrasts; Pantopaque (iofendylate), introduced in 1944, offered better tolerability and easier aspiration but still posed risks of arachnoiditis, a fibrotic inflammation of the spinal meninges, in some patients.^[14] The 1960s marked the advent of water-soluble ionic contrast agents, such as diatrizoate and iothalamate, which absorbed more readily and reduced the need for oil removal, though they caused osmotic disturbances and neurotoxicity.^[15] A major breakthrough came in 1972 with metrizamide, the first non-ionic water-soluble agent, which minimized irritation and allowed safer lumbar and cervical injections.^[16] In 1976, CT myelography was pioneered, combining intrathecal contrast with computed tomography for enhanced multiplanar imaging of spinal lesions.^[17] From the 1980s, the introduction of MRI drastically reduced myelography's routine use, as non-invasive imaging provided superior soft-tissue contrast without radiation or puncture risks.^[18] Modern non-ionic agents like iohexol, developed in the early 1980s, further improved safety by exhibiting low neurotoxicity and rapid clearance.^[16] Despite this decline, myelography's historical role was pivotal, enabling precise preoperative localization of spinal cord tumors and herniations in the pre-MRI era and advancing neurosurgical techniques through detailed anatomical insights.^[11]

Clinical Considerations

Indications

Myelography is primarily indicated for evaluating suspected spinal stenosis, where it helps delineate the degree of canal narrowing and nerve root compression that may not be fully assessed by non-invasive imaging. It is also recommended for diagnosing intervertebral disc herniation, particularly when there is clinical suspicion of nerve root impingement causing radiculopathy. Additionally, myelography aids in the detection of spinal tumors, such as meningiomas or metastatic lesions, by outlining mass effects on the thecal sac and spinal cord. Myelography is also indicated for detecting cerebrospinal fluid (CSF) leaks, such as in spontaneous intracranial hypotension, and evaluating nerve root avulsions in brachial plexus injuries. It aids in radiation therapy planning for spinal tumors.^[1]^[19]^[20]^[10] Inflammatory and infectious conditions represent key indications, including arachnoiditis, which presents with clumping of nerve roots, and spinal infections such as epidural abscesses, where myelography can confirm the extent of thecal sac involvement. Post-traumatic evaluations, such as assessing spinal cord contusions or dural tears following injury, benefit from myelography's ability to visualize subtle disruptions in CSF flow. For cerebrospinal fluid (CSF) dynamics issues, it is used to identify leaks or abnormal circulation, as in cases of spontaneous intracranial hypotension or post-surgical fistulas.^[1]^[21]^[20] Situational applications include pre-operative planning for spinal surgery, where detailed visualization of nerve root anatomy informs surgical approaches, and further evaluation of radiculopathy or myelopathy when MRI findings are inconclusive. Myelography is preferred over alternatives in scenarios requiring dynamic assessment of nerve root movement during positional changes or when MRI is contraindicated, such as in patients with non-MRI-compatible implants like pacemakers. These indications are supported by the American College of Radiology (ACR) Appropriateness Criteria, which rate CT myelography as "May Be Appropriate" for multilevel degenerative disease and suspected epidural abscess (as of the most recent available variants, referencing data up to 2019).^[10]^[21]^[22]

Contraindications

Myelography, an invasive procedure involving lumbar puncture and intrathecal contrast administration, carries specific contraindications to minimize risks such as infection, hemorrhage, and neurological complications. Absolute contraindications include active central nervous system (CNS) infection, such as meningitis, which poses a high risk of introducing pathogens into the subarachnoid space during puncture.^[10] Uncontrolled seizures represent another absolute contraindication due to the potential for exacerbation by contrast media or procedural stress.^[10] A recent lumbar puncture or prior myelogram within 1 week is a relative contraindication to avoid cumulative risks of cerebrospinal fluid (CSF) leak or hematoma formation.^[23] Severe bleeding diathesis, exemplified by thrombocytopenia with platelet count below 50,000/μL, constitutes an absolute contraindication owing to the elevated hemorrhage risk associated with needle insertion.^[10] Relative contraindications encompass conditions where the procedure may proceed if benefits outweigh risks, following careful evaluation. These include pregnancy, primarily due to fetal radiation exposure from fluoroscopy, though shielding and minimization techniques can mitigate this.^[10] An uncooperative or agitated patient increases procedural difficulty and complication likelihood, serving as a relative contraindication.^[10] Connective tissue disorders, such as Ehlers-Danlos syndrome, heighten the risk of dural tear and CSF leakage, warranting caution.^[10] Additionally, generalized septicemia or localized infection at the puncture site represents a relative contraindication to prevent systemic spread.^[10] Patient-specific risks further inform contraindication assessment. Allergies to iodinated contrast media are a significant relative contraindication, potentially leading to severe anaphylactic reactions, though premedication may allow proceeding in select cases.^[10] In patients with multiple sclerosis, myelography carries an elevated risk of symptom exacerbation or adverse neurological events from contrast interaction with demyelinated tissue.^[24] Historical or laboratory evidence of coagulopathy, such as elevated INR or recent antiplatelet therapy, also qualifies as relative, requiring correction where feasible.^[10] According to the American Society of Neuroradiology (ASNR) practice parameter (2016), preprocedural evaluation must include assessment of coagulation status via recent platelet count, prothrombin time (PT), partial thromboplastin time (PTT), and international normalized ratio (INR), alongside informed consent that explicitly outlines these contraindications and associated risks.^[10]

Types

Conventional Fluoroscopic Myelography

Conventional fluoroscopic myelography is a radiographic technique that involves the intrathecal injection of iodinated contrast medium into the subarachnoid space, followed by real-time imaging under fluoroscopic guidance to visualize the spinal cord, nerve roots, and subarachnoid spaces. The procedure utilizes a tilting fluoroscopy table to manipulate the patient's position, allowing gravity to distribute the contrast dynamically through the spinal canal for optimal opacification of targeted regions. This method provides direct assessment of contrast flow and filling defects in real time, enabling evaluation of spinal pathology such as cord compression, arachnoiditis, or nerve root abnormalities.^[10] The imaging process begins immediately after contrast administration, with the radiologist using continuous fluoroscopy to monitor the contrast column as it moves cephalad or caudad via table tilting and patient rotation. Multiple projections, including anteroposterior, lateral, and oblique views, are acquired at various spinal levels to assess the thecal sac and root sleeves comprehensively; spot films or digital images are captured for documentation. The entire imaging sequence typically lasts 30 to 60 minutes, depending on the spinal region examined and the extent of pathology. This dynamic approach allows for functional evaluation, such as observing contrast leakage or positional changes in spinal structures.^[19]^[3] Historically, conventional fluoroscopic myelography emerged as the primary diagnostic tool for spinal disorders following its introduction in 1921 by Jean-Athanase Sicard and Jacques Forestier, who first demonstrated the use of lipiodol contrast; it dominated spinal imaging until the 1970s when computed tomography began to supplant it. Despite the advent of MRI, it remains relevant today for intraoperative guidance, cases where MRI is contraindicated, or basic evaluations in resource-limited settings.^[3] Key advantages include its ability to provide real-time dynamic visualization of contrast flow, which is particularly useful for detecting filling defects in nerve root sleeves and assessing mobility of spinal elements—features less effectively captured by static imaging modalities. It is also more cost-effective than CT-based alternatives, requiring only fluoroscopic equipment without advanced scanners. However, limitations encompass a higher radiation dose compared to MRI (typically 3-7 mSv effective dose, varying by protocol),^[25] inferior depiction of bony anatomy due to overlapping structures, and image quality that is highly operator-dependent, influenced by patient cooperation and contrast distribution.^[3]^[10]

CT Myelography

CT myelography is a diagnostic imaging technique that combines the intrathecal injection of iodinated contrast material into the cerebrospinal fluid (CSF) space with subsequent computed tomography (CT) scanning to produce detailed cross-sectional images of the spinal canal, cord, and nerve roots.^[26] The procedure typically begins with a lumbar puncture to introduce the contrast, allowing it to distribute within the subarachnoid space, followed by CT acquisition that enables multiplanar reconstructions in axial, sagittal, and coronal views for comprehensive visualization of spinal anatomy.^[26] This method enhances the detection of abnormalities by outlining the thecal sac and adjacent structures with high contrast resolution.^[17] First performed in 1976 by Giovanni Di Chiro and David Schellinger, CT myelography demonstrated its utility in evaluating spinal dysraphism through computer-assisted imaging after metrizamide injection, marking a significant advancement over earlier radiographic techniques.^[27] It rapidly became the gold standard for spinal imaging until the widespread adoption of magnetic resonance imaging (MRI) in the 1980s, though it remains relevant in specific clinical scenarios.^[28] The imaging process generally involves CT scanning 1-2 hours post-injection to capture optimal contrast opacification, facilitating the assessment of subtle pathologies such as CSF leaks, small intradural tumors, or postoperative spinal changes that may be obscured in other modalities.^[26] Compared to conventional fluoroscopic myelography, CT myelography offers superior depiction of soft tissue interfaces and bony structures due to its inherent high-resolution capabilities, while certain protocols may reduce overall radiation exposure through targeted scanning.^[29] It also supports 3D modeling and rotational reconstructions, aiding in precise anatomical localization and surgical planning.^[30] Currently, it is preferred for evaluating spinal dysraphism, particularly when MRI is contraindicated or insufficient, as well as for confirming dynamic CSF dynamics or residual lesions in postoperative patients.^[27]^[31]

Regional Approaches

Myelography techniques are adapted based on the targeted spinal region to optimize contrast distribution and minimize risks, with the choice of puncture site influencing procedural safety and efficacy. The cervical approach typically involves a lateral C1-C2 or C1-C3 puncture to access the upper spinal canal directly, particularly when lumbar access is contraindicated or a complete subarachnoid block is suspected. This method requires precise needle placement in the dorsal subarachnoid space, often using a 22- or 25-gauge Quincke-type needle with the bevel oriented dorsally to reduce cerebrospinal fluid (CSF) leakage. A higher volume of nonionic contrast agent, ranging from 7 to 12.5 mL (depending on concentration, such as iohexol 180-300 mg I/mL), is injected to ensure adequate opacification of the cervical region. Risks include rare but serious complications like vertebral artery injury, with an incidence below 0.05%, potentially leading to bleeding or, in isolated cases, fatal outcomes from anomalous vascular anatomy.^[32]^[33] The lumbar approach remains the most common method, utilized in the majority of myelography procedures due to its relative accessibility and lower technical demands. It is performed at the L3-L4 or L4-L5 interspace, ideally below the conus medullaris (typically L2-L3 to L3-L4 for optimal CSF dynamics), via an interlaminar or paramedian route in the lateral decubitus or prone position. A standard contrast bolus of approximately 10 mL is administered following a test injection of 0.5 mL to confirm intrathecal placement, allowing visualization of the cauda equina and lower spinal structures. This approach is particularly suitable for beginners, as it benefits from fluoroscopic guidance and carries a lower risk profile compared to higher punctures, though postdural puncture headache (PDPH) remains a concern, mitigated by using smaller-gauge or atraumatic needles.^[10]^[33]^[34] Thoracic myelography is infrequently performed as a direct puncture due to anatomical challenges and is usually achieved indirectly through a lumbar injection combined with table tilting to direct contrast flow. In this rare approach, the patient is positioned prone or in decubitus Trendelenburg (head-down tilt of 10-15 degrees) to facilitate cranial migration of the 10 mL contrast bolus, enabling imaging of mid-spinal lesions such as tumors or CSF-venous fistulas. Fluoroscopic monitoring ensures controlled spread, avoiding excessive pressure on thoracic structures.^[3]^[33] Injection site selection depends on the spinal level of interest: lumbar punctures are preferred for lower thoracic and lumbosacral assessments, while cervical punctures target upper regions, though crossover imaging is feasible by manipulating patient positioning and table tilt to redistribute contrast without additional injections. Outcomes vary by approach; direct cervical punctures exhibit a lower PDPH incidence (milder and shorter duration, under 5% nausea rate) compared to lumbar injections for cervical run-up, which can reach 38-52% headache rates due to greater CSF disturbance. Lumbar approaches are safer for novice practitioners, with overall complication rates below 0.05% for major events when properly executed.^[32]^[35]^[36]

Special Populations

In pediatric patients, myelography requires tailored modifications to account for smaller body size and developmental considerations. Contrast agent doses are reduced and calculated based on body weight, typically ranging from 0.5 to 3 mL/kg for iohexol (Omnipaque 300 mgI/mL), with the usual dose being 1 to 1.5 mL/kg to minimize risks associated with limited cerebrospinal fluid (CSF) volume. Procedures often necessitate conscious sedation or general anesthesia to ensure patient cooperation and safety, particularly in younger children who may not tolerate the positioning or needle insertion. ^[37] Common indications include evaluation of congenital spinal anomalies, such as tethered cord syndrome or spinal dysraphism, where myelography can delineate neural elements when MRI is inconclusive. Due to the invasive nature and smaller CSF compartment, pediatric patients face an elevated risk of post-procedural infection, including meningitis, compared to adults. ^[38] For elderly patients, myelography adaptations address age-related physiological changes and comorbidities. Dosing of contrast agents is generally lowered to reduce the likelihood of adverse effects like hypotension or CSF leakage, which can be exacerbated by reduced cardiovascular reserve and spinal degenerative changes such as osteoporosis. ^[39] The procedure is frequently indicated for assessing spinal stenosis or multilevel degenerative disease, where it provides detailed visualization of neural compression in patients unable to undergo MRI due to claustrophobia or implanted devices. ^[39] Careful monitoring for postural hypotension is essential post-procedure, as older adults are more susceptible to orthostatic symptoms from CSF dynamics alterations. ^[40] In other special populations, procedural challenges and risks are amplified. Obese patients present difficulties with fluoroscopic guidance and needle placement due to increased soft tissue depth, often requiring longer needles or alternative imaging approaches to achieve accurate subarachnoid access. ^[41] Myelography is generally avoided in pregnant individuals unless absolutely necessary for maternal health, owing to fetal radiation exposure risks; if performed, abdominal shielding is mandatory to mitigate ionizing radiation. ^[42] Immunocompromised patients, such as those with HIV/AIDS, experience heightened contraindications, particularly infection risks, necessitating stringent sterile techniques and prophylactic antibiotics, though the procedure may still be warranted for excluding spinal cord compression. ^[43] Guidelines emphasize body weight-based dosing and procedural safeguards across these groups. The European Society of Paediatric Radiology (ESPR), in collaboration with the European Society of Neuroradiology (ESNR), recommends ultrasound guidance for lumbar punctures in children under 12 months to optimize needle trajectory and reduce complications during myelography initiation. ^[44] Overall, pediatric patients may experience a different profile of complications compared to adults, with higher rates of nausea and fever but potentially lower incidence of headaches, though these may be more severe. ^[38]

Procedure

Patient Preparation

Patient preparation for myelography involves several steps to minimize risks such as bleeding, allergic reactions, nephrotoxicity, and procedural discomfort while ensuring optimal imaging quality. These measures include dietary restrictions, medication adjustments, laboratory assessments, allergy screening, informed consent, logistical arrangements, and hydration protocols.^[37]^[1] Patients are typically instructed to remain nil per os (NPO) for solids for 2 to 4 hours prior to the procedure to reduce the risk of aspiration, particularly if sedation is anticipated, though clear liquids may be permitted up to 2 hours before.^[19]^[9] Anticoagulant medications must be held in advance to prevent spinal hematoma; for example, warfarin is discontinued 4 to 5 days prior with confirmation of a normal international normalized ratio (INR), while resumption occurs post-procedure under physician guidance. Anti-seizure medications are continued as prescribed to maintain therapeutic levels and reduce seizure risk associated with contrast agents.^[37] Pre-procedure laboratory screening includes a coagulation panel (prothrombin time [PT], INR, partial thromboplastin time [PTT], and platelet count) within one week for patients with hematologic disorders, serum creatinine to assess renal function, and a detailed history of iodine allergies.^[37]^[9] These tests help identify contraindications such as coagulopathy or impaired kidney function, which could increase bleeding or contrast-related nephrotoxicity risks.^[37] Informed consent is obtained after discussing the procedure's risks (e.g., headache, infection), benefits, and alternatives such as magnetic resonance imaging (MRI).^[37]^[1] Patients are encouraged to hydrate with 1 to 2 liters of clear fluids the day before to promote renal clearance of contrast and reduce nephrotoxicity, especially in those with risk factors like chronic kidney disease.^[19] Logistical preparation includes establishing intravenous access for potential medications or hydration, preparing monitoring equipment for vital signs, and offering mild sedation for anxious patients per ACR–SIR guidelines.^[37]^[1] Arrangements for post-procedure transportation are essential, as patients may experience temporary neurological effects and should not drive for 24 hours.^[9] The American College of Radiology (ACR) emphasizes pre-hydration strategies, such as intravenous isotonic saline at 1 to 1.5 mL/kg/hour starting 3 to 12 hours prior in high-risk patients, to mitigate contrast-induced acute kidney injury.

Injection and Imaging Techniques

The myelography procedure commences with sterile access to the subarachnoid space via lumbar puncture, typically performed at the L3-L4 interspace using a 22- to 25-gauge styletted spinal needle under fluoroscopic guidance to ensure precise placement.^[37] Local anesthesia is administered prior to needle insertion, and upon traversing the dura, the stylet is removed to measure cerebrospinal fluid (CSF) pressure, which helps assess for any underlying intracranial hypertension or other abnormalities.^[37] A small test injection of 0.2 to 0.5 mL of contrast material is then administered to confirm intrathecal positioning and rule out inadvertent epidural or subdural placement.^[33] Following confirmation, nonionic iodinated contrast is injected slowly under continuous or intermittent fluoroscopic monitoring to prevent discomfort, turbulence, or extravasation, with rates generally on the order of 0.1 to 1 mL per second depending on the specific technique and patient tolerance.^[10] Total volumes range from 10 to 17 mL for lumbar approaches targeting the thecal sac, with reduced amounts (e.g., 7 to 12 mL) for cervical or thoracic studies to limit the iodine dose to a maximum of 3.0 g.^[10] To achieve optimal contrast distribution, the fluoroscopy table is tilted—often into the Trendelenburg position (head-down 15 to 30 degrees)—allowing gravity-assisted antegrade flow from the lumbar site upward to the desired spinal levels, or reverse tilting for retrograde flow in cervical injections.^[37] Patient positioning, such as prone or lateral decubitus, may be adjusted to enhance layering or target specific regions. Imaging acquisition occurs in real-time during injection via fluoroscopy to visualize contrast dynamics, followed by multiplanar spot films in anteroposterior, lateral, and oblique projections to document nerve root and thecal sac filling.^[10] For CT myelography, immediate post-injection scanning uses multidetector CT with thin collimation (0.6 to 1.0 mm slices), low pitch (0.8), and multiplanar reconstructions to provide high-resolution detail of spinal anatomy.^[33] Throughout, vital signs are continuously monitored, and neurologic checks for sensation, motor function, and reflexes are performed at regular intervals to detect any immediate adverse effects.^[9] Procedural variations include antegrade flow for most lumbar-initiated studies or retrograde approaches via C1-C2 puncture when lumbar access is contraindicated, with the entire process typically lasting 45 to 90 minutes depending on the extent of imaging and contrast maneuvers.^[37] Quality control emphasizes prevention of extravasation through vigilant fluoroscopic oversight and test injections, with hybrid fluoroscopy-CT integration employed if initial views are suboptimal; historically, oil-based contrasts required aspiration of excess material post-imaging, but modern water-soluble agents are naturally resorbed.^[33]

Post-Procedure Management

Following myelography, patients receive immediate post-procedure care to minimize risks such as post-dural puncture headache and cerebrospinal fluid leakage. This typically includes flat bed rest with the head in a neutral position for 1 to 4 hours to promote CSF resorption and reduce intracranial pressure changes.^[1] Oral hydration is encouraged, with patients advised to consume 2 to 3 liters of fluids, preferably caffeinated beverages, to replenish CSF volume and prevent headaches.^[19]^[45] In the recovery area, patients are monitored for 2 to 6 hours, during which vital signs, neurological status, and any signs of complications like headache or nausea are assessed regularly.^[1]^[46] Discharge criteria generally include absence of severe headache, stable vital signs, and ability to ambulate without significant distress, allowing most low-risk patients to go home the same day.^[19]^[9] For follow-up, pain management focuses on acetaminophen for mild discomfort, while patients are instructed to report symptoms such as fever, persistent headache, leg weakness, or changes in bowel/bladder function promptly.^[46] Imaging results are typically reviewed with the referring physician within 24 hours to discuss findings and next steps.^[37] Special instructions emphasize avoiding strenuous activity for 24 hours, refraining from driving if sedation was used, and repeating laboratory tests if iodinated contrast was administered to monitor renal function.^[47]^[46] According to the ACR-ASNR-SPR Practice Parameter for the Performance of Myelography and Cisternography (revised 2013, with ongoing relevance in current practice), outpatient procedures are feasible for low-risk patients, with same-day discharge supported when appropriate monitoring and instructions are provided.^[37]

Contrast Agents

Types and Properties

Contrast agents used in myelography have evolved significantly to minimize neurotoxicity while maintaining diagnostic efficacy. Early agents included oil-based iodinated compounds such as iofendylate (Pantopaque), introduced in the 1940s, which provided persistent radiopacity but were adhesive and difficult to remove completely from the subarachnoid space, leading to a risk of chronic adhesive arachnoiditis through mechanical irritation and inflammation of the arachnoid membrane.^[48]^[49] In the 1960s, ionic water-soluble agents like meglumine iothalamate emerged, offering better CSF miscibility than oils but exhibiting high osmolality (over 1500 mOsm/kg) and significant neurotoxicity, including seizures and encephalopathy due to their hypertonicity disrupting neuronal membranes.^[50] A pivotal advancement occurred in 1972 with metrizamide, the first non-ionic water-soluble agent, which reduced osmolality to around 300-500 mOsm/kg and lowered seizure risk compared to ionic predecessors, though it still carried some neurotoxic potential, particularly in patients with seizure histories.^[16]^[51] Contemporary myelography relies on second-generation non-ionic water-soluble contrast media, such as iohexol (Omnipaque) and iopamidol (Isovue), which are the preferred agents for intrathecal administration due to their low osmolality (500-850 mOsm/kg water) and minimal neurotoxicity.^[52]^[53] These agents provide excellent radiographic opacification with iodine concentrations typically ranging from 180 to 240 mg/mL for myelographic use, allowing clear visualization of spinal structures while exhibiting low viscosity (e.g., 1.5-5 cP at 37°C depending on concentration) that facilitates smooth injection and even distribution within the cerebrospinal fluid (CSF).^[54]^[55] Their chemical stability in CSF ensures prolonged radiopacity without precipitation or degradation, and they are primarily excreted unchanged via glomerular filtration in the kidneys, with over 90% elimination within 24 hours.^[56]^[52] Selection of contrast agents for myelography is guided by safety profiles, with the U.S. Food and Drug Administration (FDA) mandating non-ionic agents for all intrathecal applications since their approval in 1985, due to the encephalopathy and seizure risks associated with high-osmolar ionic media.^[57]^[58] High-osmolar agents are contraindicated intrathecally because their osmotic effects can cause cerebral dehydration, blood-brain barrier disruption, and severe neurological complications.^[50] Iohexol and iopamidol exemplify ideal properties: non-ionic structure minimizes chemotoxicity, low osmolality approximates plasma (285 mOsm/kg), and hydrophilicity reduces protein binding and neuronal irritation.^[59]^[60] The transition from ionic agents in the 1960s to non-ionic media in the 1970s and 1980s markedly improved safety, with studies reporting a reduction in adverse reaction rates from approximately 12-15% with ionic agents to 3% or less with non-ionic ones, including a substantial decrease in severe neurotoxic events like seizures and encephalopathy.^[61]^[62] This evolution, driven by pharmaceutical advancements, has made myelography safer for routine clinical use, though complete removal of residual contrast remains unnecessary due to rapid CSF clearance.

Administration Guidelines

The administration of contrast agents in myelography requires precise dosing tailored to the injection site, patient age, and procedure type to ensure diagnostic efficacy while minimizing risks. For adult lumbar myelography, typical volumes range from 10 to 17 mL of iohexol at 180 mg iodine/mL or 7 to 12.5 mL at 240 mg iodine/mL, delivering 1.8 to 3.06 g of iodine. Cervical myelography generally uses 6 to 12.5 mL of 240 mg iodine/mL or 4 to 10 mL of 300 mg iodine/mL, corresponding to 1.2 to 3.0 g of iodine. Thoracic and total columnar approaches follow similar ranges, with 6 to 12.5 mL of 240 mg iodine/mL or 6 to 10 mL of 300 mg iodine/mL, up to 3.0 g of iodine. The maximum total iodine dose should not exceed 3.06 g across all adult procedures, as recommended by manufacturer guidelines and FDA approvals to prevent neurotoxicity.^[24]^[37] Pediatric dosing is prorated based on body weight and age to account for smaller CSF volumes, with total iodine limited to 0.36 to 2.7 g. For example, children under 3 months receive 2 to 4 mL of 180 mg iodine/mL (0.36 to 0.72 g iodine), while those aged 7 to 13 years may receive 5 to 12 mL (0.9 to 2.16 g iodine), approximating 1 mL per 5 kg of body weight adjusted for the specific concentration. Higher iodine concentrations, such as 300 mg iodine/mL, are suitable for CT myelography to enhance opacification, but volumes must remain within these limits.^[24]^[64] Injection techniques emphasize safety and controlled delivery. Contrast must be administered slowly over 1 to 2 minutes under fluoroscopic guidance following confirmation of cerebrospinal fluid (CSF) aspiration to verify needle placement in the subarachnoid space. Only non-ionic, low-osmolality agents approved by the FDA for intrathecal use, such as iohexol (Omnipaque) or iopamidol (Isovue-M), are permitted, as ionic agents carry high risks of severe adverse effects when injected intrathecally. Post-injection, the needle is removed, and the site is monitored; a saline flush may be used to clear residual contrast from the needle tract if needed.^[24]^[37]^[65] During administration, continuous monitoring for signs of patient distress is essential. The procedure should be paused immediately if severe pain, neurological changes, or seizure-like activity occurs, allowing for assessment and potential intervention. Patients with a history of mild allergic reactions to iodinated contrast may receive premedication, such as oral prednisone (50 mg at 13, 7, and 1 hours prior) and diphenhydramine (50 mg 1 hour prior), to mitigate risks, though evidence for efficacy in intrathecal use remains limited compared to intravenous applications. Regulatory standards mandate storage of these agents at room temperature (15-30°C or 20-25°C, protected from light), with a typical shelf life of 3 to 5 years from manufacture, ensuring stability for clinical use.^[24]^[66] Recent updates in professional guidelines reinforce conservative dosing to enhance safety. FDA and manufacturer guidelines limit total intrathecal iodine to 3.06 g to reduce toxicity risks, aligning with maxima in package inserts and reflecting evidence from clinical studies on neurotoxic thresholds. These protocols apply across conventional fluoroscopic and CT myelography, with brief consideration for regional approaches such as cervical injection sites where volumes are further reduced.^[66]^[37]^[67]

Risks and Complications

Common Adverse Effects

The most common adverse effect following myelography is post-dural puncture headache (PDPH), with an incidence ranging from 30% to 50% of patients. This positional headache, characterized by worsening upon upright posture and relief when supine, typically onset within 12 to 24 hours after the procedure and lasts 1 to 7 days. It results from cerebrospinal fluid leakage through the dural puncture site, leading to intracranial hypotension. Initial management involves conservative measures such as bed rest and hydration, with epidural blood patch considered for severe or persistent cases; detailed strategies are outlined in post-procedure management protocols.^[68]^[69] Nausea and vomiting occur in approximately 10% to 20% of cases, primarily due to meningeal irritation from the injected contrast agent. These symptoms are usually mild and self-limiting, resolving within 24 hours without specific intervention. Back or neck pain is reported in 20% to 30% of patients, often attributable to the needle insertion or contrast distribution along the spinal canal, and is typically managed with nonsteroidal anti-inflammatory drugs (NSAIDs).^[70]^[71] Other mild effects include low-grade fever and rigors, which may arise from transient inflammatory responses to the contrast or procedural trauma. According to studies, PDPH incidence is highest with the lumbar approach, reaching up to 40%. These common effects are generally benign and do not require escalation beyond routine monitoring, distinguishing them from rarer severe complications.^[72]^[73]^[74]

Rare and Serious Risks

Seizures represent a rare but serious complication of myelography, occurring in 0.093%–0.847% of cases when using modern nonionic contrast agents. Historically, the incidence was higher, reaching up to 5% with ionic contrast media, though such agents are no longer in use. Risk factors include patient dehydration, high contrast doses, history of epilepsy, and inadvertent intracranial contrast migration.^[53] Infectious complications, particularly bacterial meningitis, arise from breaches in sterile technique during the procedure, with an estimated incidence of 0.01%–0.1%. These infections typically involve streptococcal species from oral or respiratory flora introduced via healthcare personnel, as evidenced by outbreaks linked to absent facemask use. Prophylaxis emphasizes strict asepsis, including surgical masks for providers; antibiotics may be indicated in high-risk scenarios such as immunocompromise.^[75]^[76] Neurological sequelae are infrequent but can be severe. Arachnoiditis, characterized by inflammation and adhesions in the subarachnoid space, occurs in less than 0.1% of cases after the 1980s shift to water-soluble nonionic agents, largely a legacy of earlier oil-based contrasts like iophendylate.^[77] Epidural hematoma, potentially leading to cord compression, is extremely rare, primarily reported in case studies, and strongly associated with underlying coagulopathy. Paraplegia has been documented in isolated case reports, particularly in patients with preexisting spinal stenosis, where contrast injection exacerbates cord ischemia or compression.^[78] Other grave risks include anaphylactic reactions to the contrast agent, with severe cases like anaphylaxis occurring in fewer than 0.01% of procedures. Renal failure may ensue in patients with preexisting kidney impairment due to the iodinated contrast load, though this is mitigated by hydration protocols. Death is exceedingly rare, with rates below 0.001%, typically tied to unmanaged anaphylaxis or profound neurological events.^[79]^[80] Overall, major complications from myelography are infrequent (less than 1% based on practitioner surveys), underscoring the procedure's relative safety when performed by experienced practitioners.^[81] Informed consent is mandatory, with patients counseled on these low-probability, high-impact risks to ensure shared decision-making.

Current Role and Alternatives

Decline Due to MRI

The introduction of magnetic resonance imaging (MRI) in the mid-1980s marked a pivotal shift in spinal imaging, significantly diminishing the role of myelography due to MRI's non-invasive nature, absence of ionizing radiation and intrathecal contrast requirements, and superior soft tissue contrast for visualizing the spinal cord and nerve roots.^[3] Prior to this, myelography had been the primary modality for evaluating spinal canal pathologies since the early 20th century, but MRI's ability to provide multiplanar images without patient repositioning rapidly established it as the preferred first-line technique. MRI offers several key advantages over myelography, including the elimination of intrathecal injection risks such as cerebrospinal fluid leakage and chemical irritation, as well as enhanced detection of subtle abnormalities like cord edema and inflammation through its high-resolution depiction of soft tissues.^[3] Unlike myelography, which relies on fluoroscopy or computed tomography (CT) for imaging and exposes patients to radiation doses typically ranging from 3-4 mSv for lumbar procedures, MRI avoids such exposure entirely.^[25] Additionally, MRI's non-invasive approach reduces procedural complexity and improves patient comfort, with no need for specialized contrast administration or strict positioning during acquisition. In contrast, myelography's invasive procedure—involving lumbar puncture—carries a notable risk of post-dural puncture headache from CSF leakage, occurring in up to 30% of cases.^[1] Its limited availability stems from the need for fluoroscopic suites and trained personnel, further contributing to its decline as MRI scanners became more widespread. The American College of Radiology (ACR) Appropriateness Criteria reinforce MRI as usually appropriate for initial evaluation of conditions like myelopathy and low back pain, positioning myelography as a secondary option only in select scenarios.^[22] Usage of myelography has plummeted since the 1980s; for instance, PubMed citations related to the procedure decreased from 3,226 in the 1980-1989 decade to 987 in 2000-2009, reflecting broader clinical shifts.^[3] At one major institution, annual myelography volumes fell from 400 in 1999 to 171 in 2009, a decline exceeding 55%, underscoring MRI's dominance in routine spinal diagnostics.^[3] While myelography retains utility in cases of MRI failure, such as severe motion artifacts, its overall prevalence has contracted to a niche role in modern neuroradiology.

Remaining Indications

Myelography remains a valuable diagnostic tool in cases where magnetic resonance imaging (MRI) is contraindicated, such as in patients with non-MRI-conditional pacemakers, cochlear implants, or severe claustrophobia.^[3]^[82] The increasing availability of MR-conditional implants has reduced the number of absolute contraindications since the 2010s.^[83] In these scenarios, computed tomography (CT) myelography provides detailed visualization of the spinal canal, nerve roots, and thecal sac without the risks associated with magnetic fields or confined spaces.^[26] Beyond contraindications, myelography offers enhanced detail in specific conditions requiring dynamic assessment or where MRI is limited, such as cerebrospinal fluid (CSF) leaks, where dynamic CT myelography captures real-time contrast flow to localize high-flow leaks or ventral dural tears that static imaging may miss.^[84] It is also preferred for postoperative evaluation of spinal hardware, as metallic implants cause significant MRI artifacts that obscure neural structures, whereas CT myelography delineates hardware position, fusion integrity, and adjacent soft tissues effectively.^[3] Additionally, in traumatic brachial plexus injuries, CT myelography excels at detecting subtle nerve root avulsions, including pseudomeningoceles and intradural defects, with high sensitivity for preoperative planning.^[26] In surgical planning, myelography supports procedures like scoliosis correction by highlighting foraminal and lateral recess stenosis in degenerative cases, aiding in precise osteotomy and instrumentation decisions.^[74] For tumor resection, particularly in metastatic epidural spinal cord compression, CT myelography assists in delineating thecal sac involvement when MRI is inconclusive, facilitating separation surgery techniques.^[85] Intraoperative or preoperative CT myelography with 3D reconstruction further enhances fusion accuracy in complex deformities by providing myelographic detail integrated with bony anatomy.^[86] Emerging applications include digital subtraction myelography combined with CT for identifying CSF-venous fistulas, a type of vascular anomaly causing spontaneous intracranial hypotension, where real-time subtraction isolates subtle contrast extravasation into epidural veins.^[87] Recent outpatient protocols for dynamic CT myelography have demonstrated high procedural success, with studies reporting effective leak localization in over 90% of cases while minimizing radiation and enabling same-day discharge.^[88] Looking ahead, myelography may see revival through AI-enhanced imaging, such as patch-based machine learning models that generate virtual CT myelograms from dual-energy scans to improve CSF delineation and reduce contrast needs in complex cases.^[89] It serves as an adjunct in intricate spinal evaluations, particularly for failed fusions or multilevel pathologies where MRI falls short.^[90]

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