Transforaminal lumbar puncture for intrathecal access: Case series with literature review and comparison to other techniques

Highlights

• Review imaging to identify ideal needle trajectory, spinal level & neural foramen.

• Place scoliotic patients in lateral decubitus position with the apex of the spinal curvature up.

• Shortest needle path to neural foramen is typically at or near the apex of scoliosis.

• A smaller bore needle (ideally 22 gauge) decreases risk of CSF leak and nerve root injury.

• Direct needle into posterior and caudal aspect of foramen to avoid neurovascular structures.

Abstract

Fluoroscopic-guided lumbar puncture (LP) is a procedure commonly performed by radiologists, which in some circumstances may be difficult or impossible using a traditional posterior interspinous or interlaminar approach. Alternatives to LP include cervical and cisternal punctures, placement of an Ommaya reservoir, and lumbar laminectomy. More recently, however, there has been a move toward access of the thecal sac through a transforaminal approach in patients with challenging anatomy. This report outlines our approach and experience using transforaminal LP (TFLP) in patients with spinal muscular atrophy (SMA) with a 100% success rate. We discuss its utility in other patients with difficult access and compare TFLP with other techniques to access the intrathecal space.

Introduction

Fluoroscopic-guided LP is widely performed by radiologists using interlaminar and interspinous approaches for a variety of indications, including collecting CSF for laboratory analysis, obtaining opening CSF pressure and administration of intrathecal medications and contrast for myelography [1]. Some patients may not be viable candidates for interlaminar or interspinous LP for a variety of reasons, including scoliosis, bony fusion, hardware and overlying soft tissue infection [2], [3].

SMA constitutes a subset of patients with considerable spinal deformity and extensive posterior spinal fusion that may preclude successful intrathecal access using a traditional posterior approach LP. A rare autosomal recessive neuromuscular disorder, SMA has an estimated incidence of 1 in 10,000 live births and is reported to be the most common genetic cause of death in infancy [4]. It results from a defect in the Survival of Motor Neuron 1 (SMN1) gene that encodes the SMN protein essential for the survival of alpha-motor neurons in the spinal cord and brainstem. Survival in SMA patients is directly linked to the closely related SMN2 gene that normally produces the SMN protein in very low levels; a greater number of copies of the SMN2 gene results in less severe clinical SMA phenotype. SMA manifests with a wide spectrum of disease severity and is grouped into clinical subtypes (SMA types 0–4) based on age of onset and disease course, though all patients have progressive muscular wasting and loss of function [5].

Nusinersen is a relatively new medication used to treat SMA by targeting and potentiating the production of the SMN protein by theSMN2 gene. Approved by the United States Food and Drug Administration (FDA) for use in all types of SMA in December 2016, Nusinersenwas the first effective treatment for SMA [6], but can only be administered intrathecally. Nusinersen is administered initially as three loading doses two weeks apart, (days 0, 14 and 28), an additional loading dose at 8 weeks (day 56), and every four months thereafter. In May 2019, the FDA approved an additional single dose intravenous gene therapy for SMA, Onasemnogene, with an estimated therapeutic cost in excess of $2 million, but for use only in patients less than 2 years of age [7].

Virtually all non-ambulatory SMA patients develop rotoscoliosis in childhood, eventually requiring extensive spinal fusion (Fig. 1) [2]. This becomes a significant obstacle in obtaining intrathecal access for Nusinersen dosing, as the presence of hardware and subsequent fusion of the posterior elements can make it impossible to obtain access to the thecal sac posteriorly, despite image guidance. Alternative routes of access include an Ommaya reservoir, C1-C2 cervical puncture, cisternal puncture, and a direct window via lumbar laminectomy; however, these procedures are not without risks. Recently, a few case series have been published describing initial experiences with transforaminal lumbar puncture (TFLP) [3], [8], [9], [10], [11], [12], [13]. Experienced pediatric interventional radiologists at large academic centers may rely primarily on fluoroscopy guidance for transforaminal intrathecal nurisensen injections in complex spines [12]. However, it is currently unclear if similar rates of success are achievable with fluoroscopy guidance at smaller hospitals with lower case volumes and unavailability of CT-guidance in interventional suites for cases where fluoroscopic guidance is unsuccessful. This report describes our institutional technique and experience with the transforaminal approach in patients with SMA and its potential as a safe alternative to traditional LP in other patients.