Fluoroscopy Lumbar Puncture Assessment, Protocols, and Interpretation

Anatomy and Physiology

While performing an LP, the needle has to pass through the skin, subcutaneous fat, paraspinal fascia, muscles and then epidural fat, and the dura.[5] The thecal sac is an extension of the subarachnoid space of the brain. In the spinal canal, the thecal sac is formed by the outer dura and inner arachnoid mater. The thecal sac contains cerebrospinal fluid (CSF), the spinal cord with pia mater, and nerves. Varying amounts of epidural fat covers the thecal sac. The lumbar vertebra encloses the spinal cord, nerve roots, thecal sac, and epidural fat. The periosteum covers the vertebra and then paraspinal muscles with their fascia. The subcutaneous fat and skin are present most superficially.

Indications

Indications for Lumbar Puncture

1. A sampling of the CSF for laboratory analysis to detect infection, malignancy, inflammatory/demyelinating disorders.
2. To determine the CSF pressure in suspected cases of increased intracranial pressure (infection, malignancy, or idiopathic intracranial hypertension).
3. Chemotherapy drug administration into the thecal sac
4. Myelography and cisternography.
5. Blood patch for CSF leak
6. Baclofen administration as a pump trial.
7. Lumbar shunt placement procedure.

Indications for Fluoroscopy-guided Lumbar Puncture 

1. Failed bedside attempt (most common indication).
2. Obesity
3. Prior lumbar spine surgery/hardware
4. Severe degenerative spinal disease and scoliosis.
5. Lack of training to do the procedure.
6. Patients request to avoid failed attempts, particularly after the first failed attempt.

Contraindications

1. Coagulopathy and anticoagulants: Guidelines are available to follow during day-to-day practice.[6][7] For general-purpose discussion, any uncorrected coagulopathy can cause a spinal hematoma resulting in the spinal cord or nerve compression, which may require emergent surgery for decompression. Patients must have the INR corrected to <1.5 and have the platelet count > 50000. The aPTT in patients receiving unfractionated heparin should be more than 1.5 x normal.

Warfarin

• Warfarin to be held for 5 days, and INR is confirmed at 1.5 or less.
• Warfarin resumed within 12-24 hr after the procedure.

Heparin

• Unfractionated subcutaneous or IV heparin - wait for at least 4 hr after the previous dose and check aPtt, resume 1 hr after the procedure.

Lovenox

• Withhold the last dose or wait for 24 hr after the previous dose. Resume 6 hrs after the procedure.

Fondaparinux

• Withhold 48 hrs before the procedure. Resume therapy after 6 hrs.

Rivaroxaban

• Withhold 48hrs before the procedure. Resume therapy after 48h.

Argatroban and Desirudin

• Wait for 4 hrs after the last dose to do the procedure. Resume therapy after 1 hr.

Aspirin

• 81 mg "baby" aspirin daily, no contraindication. 325 mg/day, withhold for 5 days.

Clopidogrel

• Withhold 5 days. Resume immediately.

Ticlopidine

• Withhold 5 days.

Abciximab

• Withhold 5 days.

2. Increased intracranial pressure due to CSF obstruction: If prior imaging is not available, obtain MRI or head CT.[8]

Relative Contraindications

• Weight limit: Newer fluoroscopy tables have a weight limit of 400 pounds. Excess weight can potentially damage the fluoroscopy table hydraulic mechanism.
• Infection: A superficial infection of the lumbar region's skin is a relative contraindication because of the risk of meningitis.[9]
• Unstable and uncooperative patient: Appropriate sedation may help patients not move during the procedure. However, sedation can reduce the ability of the patient to respond if there is an injury to the nerve or spinal cord.
• Pregnancy is also a relative contraindication, given the risk of radiation to the developing embryo.

Equipment

In addition to the fluoroscopy instrument, preferably with a biplane camera or a C-arm, a standardized LP kit is required. It contains a 22 or 25 gauge spinal needle, 10 ml of Lidocaine 1%, gauze pieces, paper drapes, skin disinfectant material, and a short 25 gauge needle for the lidocaine subcutaneous administration. The regular spinal (Quincke) needle is a traumatic needle with a cutting bevel. The Sprotte or Whitacre needles are non-traumatic needles. The choice of the needle depends on the physician's preference and training. Both types of needles have pros and cons. Although the non-traumatic needles have fewer chances of post lumbar puncture headache, they are difficult to maneuver and assess the depth. Therefore, the 22 or 25 gauge size needles are commonly used. Typically a 3.5 inches needle is sufficient, but a long needle with a length of 5.5 inches should be available if required.

Personnel

A physician, physician assistant, fluoroscopy technician, and nurse are usually involved. The nurse can monitor blood pressure, respiration, secure an IV line, and, if required, administer sedation and other medications.

Preparation

Consent: LP requires written and informed consent. Health care proxy can provide consent if the patient is not able to give the consent. In emergency settings, the referring physician deems it a medical necessity and includes it in the charts. Pre-procedure patient assessment: The physician should make a checklist containing indications, contraindications, and patient's medical and mental status, appropriate written and informed consent by the patient or health care proxy. The checklist should also include the patient's weight, positioning, prior attempts, pregnancy, allergies, medications, hardware in the lumbar spine or previous surgery, infection in the back. It is vital to ensure the need for sedation, availability of a fluoroscopy table and procedure room, amount of CSF removed. Prior confirmation of privileges and authorization with the referring provider for the admission requirement in the hospital or emergency settings to treat any potential complications.

The procedure requires a high-quality fluoroscopic imaging facility. It should consist of a tilt table with a suitable support device and a capacity of 30 degrees of angulation in the downward head direction if a myelogram is also part of the procedure. It is crucial to ensure if the patient can fit on the fluoroscopy table before scheduling. If the patient's weight exceeds the capacity of the table, the table may not tilt or move, leading to the failure of the hydraulics mechanism. It is vital to ascertain the availability of necessary materials and personnel to treat adverse reactions and complications.

A brain MRI or CT head imaging within the last 30 days usually excludes a mass, mass effect, or hydrocephalus. If prior imaging is not available, obtain a brain MRI or head CT. LP can potentially cause cerebral herniation by lowering the intracranial pressure. A physician or physician assistant should perform a physical examination. Any prior imaging of the lumbar spine, such as CT, MRI, or radiographs, is also essential to review.

Assessment from the previous spine imaging helps decide the optimum puncture level of the procedure. Recent surgical scar or nearby infection precludes LP at that site. Prior spine imaging avoids spinal stenosis levels, which can cause more pain. Prior lumbar spine imaging helps estimate the skin to thecal sac distance, though generally decreases cranially. If lumbar processes are not palpable, then the regular 3.5-inch needle may not be sufficient. To estimate the appropriate needle length approximately predicts the skin-canal disease (inches) = 0.077 x BMI + 0.88.[10] It is often helpful if another person can gently compress the soft tissues on the back to reduce the skin-thecal sac distance.

Technique or Treatment

Adequate positioning of the patient is essential to make the patient comfortable and for the interventionist to perform the procedure safely. Many patients referred for the FGLP are generally hospitalized and have several comorbidities, and it is difficult for them to maintain still for a longer duration. In addition, many of them can have difficulty breathing or arm pain in certain positions.

Prone Approach: The patient should lie prone on the fluoroscopy table. Pillows straighten the lumbar lordosis when placed below the stomach. It also increases the interspinous distance, often narrowed due to degeneration. Secondly, it flattens the extra adipose tissue over the back and allows a shorter needle in most patients. A regular AP radiograph of the lumbar spine obtained before the procedure provides details of degenerative disease. Additionally, it is helpful to tilt the tube cranially by 10-15 degrees to align with the spinous process, mainly in older patients who have a reduced inter-spinous distance by degenerative disease. The prone position allows keeping the needle hub directly over the needle tip. It removes the parallax. A cross-table lateral view can confirm the depth and trajectory of the needle if a biplane camera is not available.

Prone Oblique Approach: The patient in the oblique lateral position and the spinous processes are not midline. The inter-laminar and inter-spinous spaces appear wider than in the prone approach. Many radiologists favor this approach as patients with comorbidities better tolerate this position; however, the trajectory of the needle is difficult to assess on the lateral view.

Lateral Approach:  A lateral decubitus position is a preferred position if the patient can't lie on their stomach because of obesity, backache, respiratory discomfort, shoulder pain, or medical conditions such as high blood pressure. The disadvantage is that this requires a newer biplane camera unit that is not universally available. Mobile single plane C-arm serves the same purpose, instead of newer biplane machines.[8][11]

It is vital to make the wheal right at the site of entry. For example, a small metallic object or the tip of a needle marks the entry site with the help of fluoroscopy. Lidocaine HCL, 1% concentration, is injected using a 25 gauge needle for several millimeters into the subcutaneous tissue to create a wheal. After numbing the skin, local lidocaine via a 3.5 inch 25 gauge spinal needle is injected to gradually numb the deep fascia, muscles, and ligaments, periosteum under fluoroscopic guidance after confirming that the needle is not within the dura. Combining 1 ml of bicarbonate with 4-5 ml of lidocaine reduces the initial stinging of lidocaine. The LP needle should not be used to administer the lidocaine to avoid accidental injury to the spinal cord and nerves. Most physicians prefer 20 and 22 gauge needles with a length of 3.5 inches (8.8 cm). However, in some situations, such as individuals with obesity,  longer needles with a length of 14 cm (5.5 inches) are required. Longer needles are also difficult to steer. The larger gauge spinal needles, more than 22 gauge, are challenging to navigate. Only the introducer of the coaxial system with a smaller gauge such as 18 gauge is helpful to reach the thecal sac without penetrating. Then the 22 or 25 gauge needle is entered into the thecal sac via the introducer.The needle has a hub and beveled tip. The hub has a notch on the same side of the bevel. The notch of the needle acts as a marker and corresponds to the direction of the bevel. The sharp tip steers the needle. Hence, to direct the needle in the desired direction notch should be on the opposite side.

We insert the needle in the inter-laminar space, an oval area of radiolucency on either side of the spinous process. The entry site should be directly above the inter-laminar area and marked with a narrow tip surgical pen; if performed accurately, correct marking of the entry site dramatically reduces the procedure time and patient discomfort. We insert the needle with the notch on the opposite to the physician's side.Bracing hands against the patients' back during the needle advancement is essential to avoid patient movement and sudden jerks. We initially advance the needle every 1 cm before checking for the needle tip and the hub position on fluoroscopy and avoiding parallax as much as possible. Then we rotate the needle by 1/4th circle to ensure that the needle traverses in a straight line. The prone approach visualizes the entire length of the needle trajectory on the cross-table lateral view. So we do not hesitate to obtain a lateral radiograph whenever a biplane camera is not available. The deviation of the needle path from the desired course can result in repeat attempts and delays and patient discomfort.

Once the needle crosses the paraspinal muscles, we check the needle positioning every mm while the needle is advancing through ligamentum flavum. We frequently check for the CSF flow by removing the stylet. We recommend keeping the bevel parallel to the long axis of the nerves while penetrating the dura. After the dural puncture, you get the sensation of giving off. Then rotating the needle perpendicular to the nerves eases the CSF flow. It is important to remember that the stylet should be within the needle every time before advancing or rotating. Immediately deep into the ligamentum flavum, there is the thecal sac with variable amounts of epidural fat; hence the needle can quickly enter the thecal sac and impress the nerve, causing shooting pain in the extremity. We ask patients to speak up if they feel radiating focal sharp pain shooting down the extremity when the needle touches the nerve root. The pain should stop immediately after withdrawing the needle by 1 mm, and CSF should flow. If the pain does not subside even after removing for a few minutes, we recommend using a different approach.

The CSF pressure measured in a lateral decubitus position ranges between 6-20 cm of H20 in adults and greater in patients with obesity up to 25 cm H2O. If the patient is not in the lateral place, adding the length of the needle to the pressure is needed. The opening pressure of > 25 is diagnostic of idiopathic intracranial hypertension in an appropriate clinical scenario.[12] For the standard diagnostic LP, 8 to 15 ml of CSF in 4 transparent tubes is sufficient, and CSF in the last tube is ideal for the cytological examination [8]. By removing 15-20 ml CSF, patients with idiopathic intracranial hypertension report immediate symptom improvement and is a safe and diagnostic approach. A dry tap is when the needle is within the spinal canal, but CSF does not flow. It occurs commonly with hospitalized old-age patients. It happens with epidural lipomatosis, arachnoiditis, and prior surgery, or severe spinal canal narrowing. Sometimes the CSF is too thick for the needle due to cells such as in infection or malignancy. The CSF is rechecked after asking patients to cough or performing Valsalva maneuvers. Tilting down the foot end of the table by 45 degrees after securing the patient can also be performed. A mild, short-duration suction with a 10 ml syringe may help obtain the CSF. If all attempts failed, CT-guided LP or cervical puncture could be performed.[11]

Complications

Vasovagal syncope: Patients can experience a hot feeling, the feeling of throwing up during the procedure, which is generally reversible after taking a short break.

Herniation: Although it is highly uncommon to occur, post puncture uncal herniation is an essential and dangerous complication. CT or MRI of the head is recommended before lumbar puncture to rule out obstructive hydrocephalus.

Nerve injury: LP can cause direct harm to the roots of the cauda equina.

Spinal cord injury: LP needles can damage the conus, especially in low-lying conus or achondroplasia. It is best to consult neurology, neurosurgery in these patients.

Meningitis: Proper techniques of disinfection avoid infection.

Headache: Typically, 20 or 22G needles have a reported incidence of 2.2% for FGLP while varies between 20.5 to 26.4% under blind technique.[13] The headache takes one day to appear, peaks after an additional day, and takes one day to disappear. Post lumbar puncture headache increases with lower gauge needles. Unlike cutting Quincke needles (regular spinal needles), non-cutting Sprotte or Whitacre needles cause fewer headaches. Single dural puncture and replacing the stylus before withdrawing the needle decreases the probability of post-spinal headache. The bevel position perpendicular to the long axis of the nerves while entering the dura also reduced the risk of headache.[14][15] 

Many patients improve without any treatment.[16] Although advised and practiced universally, the strict bed rest after the LP has no demonstrable bearing on the headache; however, patients generally are recommended to take 2-hour bed rest.[17] Caffeine may help reduce the headache.[18] In refractory cases, a fluoroscopy-guided epidural blood patch is an effective treatment.[19]

Vascular injury: A long needle can injure the posterior wall of the aorta by passing through the intervertebral disc, causing hematoma and pseudo-aneurysm. When the needle penetrates the aortic wall, fresh arterial blood spurts through the needle, the needle also pulsates along with the aortic pulsations. A lateral radiograph can confirm the retroperitoneal extent of the needle. When the arterial injury is suspected, we recommend consulting a vascular surgeon. It is essential to closely monitor the patient for hemodynamic stability. The reduction of the aortic pressure also helps to stabilize the hematoma. CT angiogram can be performed to look for active extravasation and stability of the hematoma. If the hematoma is felt to be stable, consider slowly removing the needle and then placing the patient supine for the tamponade effect on the aorta to stabilize the hematoma.[20]

Radiation: The average procedure time for the FGLP ranges between 12 min (range 12-30 min, SD 6) and the average radiation dose area product DAP of 10 Gy×cm(2) (range 0.1-70, SD 11) and average effective dose estimate of 2.9 mSv (range 0.9-9.4, SD 1.9).[21]

Clinical Significance

LP is one of the most common bedside procedures performed in the office, emergency department, or inpatient location. LP is required to diagnose infection, demyelinating process, malignancy, and also for myelography and cisternography. Additionally, LP is performed for therapeutic purposes to reduce intracranial pressure in patients with idiopathic intracranial hypertension.

There is an increase in the need for FGLP due to the increasing number of patients having spine surgery, high BMIs, or due to multiple failed blind attempts, or fear of failed attempts. FGLP is associated with a reduced rate of failure of LP in patients who have high BMI, prior surgery, or significant degenerative disease.[10] FGLP has advantages of image guidance that can track the needle trajectory, reduce the number of attempts, reduce the chance of blood tap, and reduce the time required for the procedure.[4]

Enhancing Healthcare Team Outcomes

FGLP is a significantly superior procedure to blind LP. It is associated with reduced postlumbar puncture headache (Level 1).[13] FGLP is a moderately skilled procedure and might injure patients significantly due to spinal cord injury if not performed correctly. Hence, it is essential to master the technique of the FGLP to obtain desired results safely. It is important to note that sedation doesn't always benefit the patient, as patients can not tell if they had root pain while steering the needle within the spinal canal.

FGLP is a commonly performed procedure in radiology departments either for diagnostic or therapeutic purposes. We generally recommend that the clinical team try at least one attempt using the nonimage-guided bedside LP; however, this will negatively impact the radiology department.[2] [Level 3]

The interprofessional clinical team requesting FGLP should understand this implication and comprehend that the clinicians might lose the skill of blind LP in the future. Clinicians should be aware of the contraindications and complications of the FGLP. It is important to note that FGLP is not immune to the complications of blind LP; however, they occur less frequently. Experienced nursing staff can assist the clinicians during the procedure and perform patient monitoring. Interprofessional coordination and communication will yield the best results from these diagnostic tests. [Level 5]