Prolapsed Lumbar Nucleus Pulposus Case File

Prolapsed Lumbar Nucleus Pulposus Case File

Eugene C. Toy, MD, Lawrence M. Ross, MD, PhD, Han Zhang, MD, Cristo Papasakelariou, MD, FACOG

CASE 33

A 54-year-old man complains of lower back pain that radiates down the back of his right leg. He states that the pain increases when he coughs or lifts objects but decreases when he lies down. He denies having experienced trauma to his back. On examination, the strength and sensation of his lower extremities are normal. During the examination, while the patient is lying on his back (supine), he complains of severe pain when his right leg is raised by the clinician.

⯈ What is the most likely diagnosis?

⯈ What is the anatomical mechanism for this condition?

ANSWER TO CASE 33:

Prolapsed Lumbar Nucleus Pulposus

Summary: A 54-year-old man has lower back pain that radiates down the back of his right leg, is exacerbated by intraabdominal pressure (Valsalva maneuver), and is relieved by rest. He denies trauma. The neurological evaluation is normal, but his pain is elicited by raising a straightened right leg.

• Most likely diagnosis: Herniated lumbar disk (prolapsed lumbar nucleus pulposus)

• Anatomical mechanism for this condition: Ruptured intervertebral disk impinging on the nerve root as it exits from the vertebral canal

CLINICAL CORRELATION

This patient experiences pain radiating down the back of his leg in the distribution served by the sciatic nerve. Hence, the syndrome is referred to as sciatica. The pain is caused by impingement of the nerve roots contributing to the sciatic nerve (L4−S3). He has no history of trauma, and we do not have details of his occupation. Heavy lifting is often an associated factor. The pain is worsened by increased intraabdominal pressure (Valsalva maneuver); thus, coughing and straining often exacerbate the symptoms. The straight leg raising maneuver elicits pain. Because this patient does not have neurological deficits, conservative therapy would include rest, physical therapy, and nonsteroidal anti-inflammatory agents. Most patients improve with this treatment. Lack of improvement, neurological deficits, or history of trauma or malignancy usually necessitates imaging of the spine. MRI is considered to be the most accurate means of examining this region.

APPROACH TO:

The Spine

OBJECTIVES

1. Be able to identify the features of a typical vertebra and the intervertebral joints

2. Be able to label the components of the spinal nerve from spinal roots to primary rami

3. Be able to locate sites where components of the spinal nerve can be compressed

4. Be familiar with the dermatomes and the landmarks of the lower extremity

DEFINITIONS

SUPINE VERSUS PRONE: Supine is the position of lying on one’s back, whereas prone is lying on one’s stomach.

HERNIATE: To push through a containing membrane or tissue.

SCIATICA: Syndrome caused by irritation to the roots (radiculopathy) of the sciatic nerve.

SYMPHYSIS: A secondary cartilaginous joint, in which two cartilaginous surfaces are held in place by a fibrous connective tissue, such as the intervertebral disk.

DISCUSSION

The vertebral column is a series of individual bones that are stacked vertically and held together by ligaments and muscles. There are 32 to 34 vertebrae (7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 3 to 5 coccygeal). The joints between each vertebra provide flexibility, but the vertebrae are held tightly in place by numerous supporting ligaments that provide strength and stability (Figure 33-1).

The main features of a typical vertebra are the tubular body and the posterior arch that surrounds and protects the spinal cord. The arch is composed of pedicles that arise from the vertebral body and lamina that join at the midline. Each vertebra has seven processes: three serve as attachment sites for muscles, and four serve as articular surfaces for adjacent vertebrae. The two transverse processes arise from the arch, where the pedicles and laminae meet. One spinous process emerges from the middle of the posterior arch.

Two types of joints support the articulation of adjacent vertebrae. The flat surfaces of the vertebral bodies join through a secondary cartilaginous joint, or symphysis. The bones themselves are separated by the intervertebral disc, which has an outer fibrous layer, the anulus fibrosus, that surrounds a soft inner layer, the nucleus pulposus. The disc provides support for the joint but also provides flexibility and a cushion against the weight of the upper body. Secondary support is provided by the four articular processes. These processes also emerge from the posterior arch. Two are

Figure 33-1. Major vertebral ligaments.

directed superiorly and two inferiorly. The superior and inferior processes of adjacent vertebrae join to form a zygapophyseal joint. This synovial joint provides strength with a limited amount of flexibility.

The pedicle and superior articular process together form a notch that is complemented by a second notch formed by the pedicle and inferior process. When two vertebrae are in apposition, the superior and inferior notches form the intervertebral foramen. This space is where spinal nerves emerge from the spinal cord to supply peripheral structures.

Peripheral nerve fibers arising from the spinal cord as anterior (ventral) roots are primarily motor, whereas the posterior (dorsal) roots are primarily sensory. These roots join to form the spinal nerve. In the cervical spine, the roots travel laterally to leave the vertebral column. The spinal nerve splits to form two mixedfunction branches, a small posterior primary ramus and a larger anterior primary ramus. Nerves emerging from lower levels of the spinal cord course inferiorly before they exit. This is because the cord itself stops at about vertebral level L1. Therefore, the roots must travel nearly straight inferiorly before forming the spinal nerves of the lower lumbar, sacral, and coccygeal regions. As these numerous roots stream inferiorly, they form the cauda equina.

The symphysis between vertebral bodies is normally very strong because the intervertebral disk is reinforced by anterior and posterior longitudinal ligaments. However, in some people, these ligaments weaken, and the intervertebral disk pushes through. If so, the roots may be compressed by the nucleus pulposus through the weakened anulus. The most common result is stimulation of pain fibers in posterior roots. More serious cases may result in paresthesia (area of localized numbness), but rarely is motor function disrupted.

Although the actual site of injury is proximal, the brain perceives the information as coming from the region of the body innervated by the compressed root. Thus, with lumbar herniations, the distribution of this type of pain (radicular pain) tends to follow the dermatomes of the lower extremity. These areas progress on the anterior surface from L1 in the inguinal region to L4 at the knee and medial leg and to L5 along the lateral leg. On the posterior surface, S1 is lateral on the thigh and leg, and S2 is medial. S3 through S5 are perianal. Sensory fibers from a given spinal level spread into adjacent dermatomes. Therefore, in order to achieve complete numbness of a single dermatome, three adjacent spinal nerves must be anesthetized.

In this case, the patient experienced pain when, in the supine position, his straightened leg was raised. This sign indicates that slight mechanical stretching of the sciatic nerve is sufficient to enhance the effect of the herniated disk. Dorsiflexion of the foot exacerbates the pain. In some patients, straightening the contralateral leg may also cause pain in the affected leg, thus confirming radiculopathy.

Radiographic imaging can be used to confirm the herniation. Currently, the best modality is magnetic resonance imaging (MRI) because the herniation can be observed directly and MRI is a noninvasive procedure. With the widespread use of MRI, it has become clear that many herniated disks are asymptomatic. An older technique, myelography, is also used on occasion. This technique takes advantage of the fact that the dura mater covers the spinal roots and proximal spinal nerve. Injection of contrast medium into the cerebrospinal fluid (CSF) will infiltrate to the spinal nerves. Therefore, compressed nerve sheaths will not be filled by the dye, and the herniated disc can be observed indirectly.

COMPREHENSION QUESTIONS

33.1 A 34-year-old woman is undergoing cystoscopic examination under spinal anesthesia. As the anesthesiologist places the needle into the subarachnoid space to inject the anesthetic agent, the needle traverses various layers. Which of the following describes the accurate sequence of layers from skin to subarachnoid space?

A. Skin, supraspinous ligament, interspinous ligament, posterior longitudinal ligament, dura mater, subarachnoid space

B. Skin, supraspinous ligament, interspinous ligament, dura mater, subarachnoid space

C. Skin, supraspinous ligament, intertransverse ligament, arachnoid space, subarachnoid space

D. Skin, interspinous ligament, anterior longitudinal ligament, dura mater, subarachnoid space

33.2 A 45-year-old man complains of shooting pain down his right leg that worsens with sitting and coughing. He also has some numbness in the area. The physician tests sensation on the lateral thigh region. Which of the following nerve roots is being tested?

A. L1 and L2

B. L2 and L3

C. L4 and L5

D. S1 and S2

E. S3 and S4

33.3 A 50-year-old diabetic man is having difficulty voiding urine. On examination, he has decreased sensation of the perineal region. Which of the following reflexes is the most likely to be affected?

A. Patellar tendon

B. Achilles tendon

C. Cremaster

D. Anal wink

ANSWERS

33.1 B. The sequence of structures is skin, supraspinous ligament, interspinous ligament, dura mater, and subarachnoid space.

33.2 C. The lateral thigh is innervated by nerve root L5.

33.3 D. The sensory fibers affected are S2 through S4, which innervate the perineal region and supply the afferent limb of the anal wink reflex.

ANATOMY PEARL

⯈ The vertebral column consists of 34 vertebrae: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 3 to 5 coccygeal.

⯈ Peripheral nerve fibers emerging from the spinal cord as anterior (ventral) roots are primarily motor, whereas the posterior (dorsal) roots are primarily sensory.

⯈ The dermatomes of the lower extremities are L1 in the inguinal region and L4 at the knee and medial leg and L5 along the lateral leg. On the posterior surface, S1 is lateral on the thigh and leg, and S2 is medial. S3 through S5 are perianal.

References

Gilroy AM, MacPherson BR. Atlas of Anatomy, 2nd ed. New York, NY: Thieme Medical Publishers; 2012:14−15. 

Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy, 7th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:464−465, 474−476. 

Netter FH. Atlas of Human Anatomy, 6th ed. Philadelphia, PA: Saunders; 2014: plates 155−159.

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