Twinned nerve roots and their vulnerability to lateral recess stenosis: a case report

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J Korean Soc Geriatr Neurosurg. 2025;.jksgn.2024.00108

Publication date (electronic) : 2025 March 4

doi : https://doi.org/10.51638/jksgn.2024.00108

Jun-Yong Cha, Sang-Soo Choi, Sung-Bum Kim, Seong-Su Ban, Jun-Hyoung Lee, Il-Tae Jang

Department of Neurosurgery, Gangnam Nanoori Hospital, Seoul, South Korea

Corresponding Author: Jun-yong Cha, MD Department of Neurosurgery, Gangnam Nanoori Hospital, 731 Eonju-ro, Gangnam-gu, Seoul 06048, Korea Tel: +82-2-1688-9797; Fax: +82-2-3448-0213; E-mail: timjunyongcha@gmail.com

Received 2024 October 28; Revised 2024 November 9; Accepted 2024 December 11.

Abstract

Introduction

Lateral recess stenosis (LRS) refers to a narrowing of the spinal canal at the point where nerve roots exit the vertebral column, typically caused by degenerative changes. When twinned nerve roots, a rare congenital anomaly, co-occur with LRS, patients may experience more severe symptoms. The coexistence of these two conditions can complicate the diagnostic process and pose unique challenges for management. This case report presents a rare case of symptomatic LRS coexisting with twinned S1 nerve roots in 67-year-old patient, managed through surgical intervention with excellent postoperative results. This case report aims to increase awareness of this rare but clinically significant condition and offer insights into its management.

Case Report

A 67-year-old female presented to the outpatient clinic with a chief complaints of severe low back pain, radiating to her left lower limb, persisting for 3 months. These symptoms were not relieved by the medication, physiotherapy, rest or epidural steroid injection. She experienced significant difficulty walking and moving.

On the examination, no visible deformity or tenderness over the spine was noted. Her back pain scored 6/10 on the numerical rating scale (NRS), with radiating pain to the left leg scoring 8/10 on NRS. The patient showed diminished reflexes and paresthesia along the left S1 dermatome. Magnetic resonance imaging (MRI) of the lumbosacral spine revealed mild LRS compressing left S1 nerve root (Fig. 1).

Fig. 1.

T1-weighted (A, C) and T2-weighted (B, D) images reveal left-sided lateral recess stenosis at the L5/S1 level (black arrows).

She was consented and scheduled for left L5/S1hemilaminectomy under general anesthesia. Intraoperative findings included a hypertrophic ligamentum flavum crowding a lateral recess and duplicated L5 nerve roots passing through the same intervertebral foramen (Fig. 2). Postoperatively, the patient reported complete pain relief, regained mobility, and was discharged on the fourth postoperative day.

Fig. 2.

Intraoperative image shows twinned S1 nerve roots (black arrows) exiting from the left S1 intervertebral foramen. The white arrow indicates the thecal sac. Written informed consent was obtained for publication of this case report and accompanying images.

Discussion

Lumbosacral nerve root anomalies (LSNRA) are rare congenital variations that affect the path or morphology of nerve roots. These anomalies are classified into four types based on their anatomical courses (Fig. 3) [1,2]. Type 1 anomalies, the most common, involve conjoined roots, with type 1A characterized by roots sharing a common dural sheath, while in type 1B, the roots have close origins but separate sheaths. Type 2 anomalies involve redundant roots, where two roots exit through one intervertebral foramen. If only one foramen is occupied (type 2A), another remains empty, but if an extra root is present (type 2B), all foramina are filled. Type 3 anomalies feature normal roots connected by an anastomotic communication between adjacent roots. In type 4 anomalies, 2 adjacent roots merge after exiting the thecal sac, forming a single nerve root that passes through the neural foramen. Recognizing these variations is essential for diagnosing and managing conditions like radiculopathy or nerve compression and for planning spinal surgeries.

Fig. 3.

Schematic representation showing lumbosacral nerve root anomalies classified by Neidre and Macnab (type 1,2 and 3) and Burke et al. (type 4). Type 1 anomalies, the most common, involve conjoined nerve roots. In Type 1A, the roots share a common dural sheath, while in type 1B, they originate closely but have separate sheaths. Type 2 anomalies involve redundant roots, where 2 roots exit through a single intervertebral foramen. In type 2A, one foramen is occupied while the other remains empty, whereas in Type 2B, the presence of an extra root ensures that all foramina are filled. Type 3 anomalies feature normal roots connected by an anastomotic communication between adjacent roots. In type 4 anomalies, 2 adjacent roots merge after exiting the thecal sac, forming a single nerve root that passes through the neural foramen.

LRS refers to the narrowing of the lateral portion of the lumbar spinal canal, which is bordered laterally by the pedicle, posteriorly by the superior articular facet, and anteriorly by the vertebral body, endplate margin, and disc margin [3]. The most common causes of LRS are degenerative spinal changes, including facet joint osteoarthritis, hypertrophy of the ligamentum flavum, intervertebral disc degeneration, and the development of endplate spurs [4]. LRS severity is typically graded using Bartynski’s classification (Fig. 4) [5]. Grade 0 indicates a normal lateral recess, where the nerve root is surrounded by cerebrospinal fluid with no contact with surrounding structures. Grade 1 shows narrowing of the lateral recess without any deviation of the nerve root. Grade 2 features narrowing with root deviation, while grade 3 indicates nerve root compression.

Fig. 4.

Schematic representation showing Bartynski’s classification of left-sided lateral recess stenosis. Grade 0 represents a normal lateral recess, with the nerve root fully surrounded by cerebrospinal fluid and no contact with surrounding structures. Grade 1 shows lateral recess narrowing without displacement of the nerve root. Grade 2 involves narrowing accompanied by root displacement, and grade 3 indicates nerve root compression.

In this case, the MRI revealed grade 1 LRS and the intraoperative finding showed twinned S1 nerve roots. Grade 1 LRS would typically not cause symptoms; however, the presence of twinned S1 nerve roots within the lateral recess increased the neural tissue volume, making the roots more susceptible to compression from even mild degenerative changes and leading to more severe symptoms than in patients with typical anatomy. This highlights the importance of integrating clinical, radiologic and surgical evaluations, as imaging alone may not reliably confirm the diagnosis [4]. MRI remains the gold standard for identifying LSNRA, as it provides detailed images of nerve root morphology, the spinal canal, and surrounding structures. Specific MRI features such as the sagittal shoulder sign, fat crescent sign, corner sign, and parallel sign may aid in identification of LSNRA [6,7], although its diagnostic sensitivity is debated [8]. Another valuable imaging modality is MR neurography, which follows the nerve roots along their longitudinal axis [9], offers detailed visualization of these variations.

The decision-making process for the operative management of LSR and LSNRA largely depends on the neurological condition of the patient. Asymptomatic and incidentally diagnosed cases typically do not require surgical intervention. However, symptomatic cases necessitate surgical treatment to alleviate neurological symptoms. When conservative treatments fail to provide relief, surgical excision becomes the preferred option. The main objective of surgery is spinal decompression, achieved by carefully exposing, visualizing, and mobilizing the affected nerve roots. In addition, adequate exposure is essential to avoid excessive traction on the nerve root and thecal sac, ensuring a safe and effective outcome [8,10].

Conclusion

Twinned nerve roots represent a rare congenital anomaly that may predispose individuals to symptomatic LRS. This condition illustrates the importance of recognizing anatomical variations in the lumbosacral spine, as they can complicate the clinical presentation and affect treatment outcomes. Thorough clinical and radiologic evaluation with understanding of spinal anatomy are crucial, especially in cases involving anatomical variations, to ensure accurate diagnosis and optimal treatment outcomes. When conservative measures fail, surgery tailored to the patient’s unique anatomy can provide relief and restore function.

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