Lumbosacral Plexopathy Diagnosis and Management

Causes

• Entrapment neuropathies are common causes of lumbosacral plexopathy resulting from spinal or extraspinal compression 1
• Piriformis syndrome is a frequently described cause of extraspinal nerve entrapment, where the sciatic nerve is compressed by the piriformis muscle due to anatomic variation or an associated fibrous band 1, 2
• Primary tumors of the lumbosacral plexus are most commonly benign peripheral nerve sheath tumors (schwannomas and neurofibromas) 2, 3
• Malignant peripheral nerve sheath tumors are rare and occur more frequently in patients with neurofibromatosis 2
• Non-neoplastic masses that can involve the plexus include hematoma, abscess, aneurysm, amyloidosis, and endometriosis 3, 4
• Acute inflammatory demyelinating polyneuropathy (Guillain-Barré syndrome) can present with lumbosacral plexopathy 3
• Chronic inflammatory demyelinating polyneuropathy (CIDP) may affect the lumbosacral plexus 3, 5
• Ischemic nerve injury can lead to lumbosacral plexopathy 3
• Hereditary neuropathies (e.g., Charcot-Marie-Tooth disease) may present with plexopathy 3
• Sarcoidosis can involve the lumbosacral plexus 3
• Infectious causes (e.g., zoster-associated limb paresis) can affect the plexus 3

Clinical Features

• Pain distribution crosses multiple dermatomes, distinguishing it from radiculopathy 6
• Weakness occurs in regions innervated by multiple nerves from the affected plexus 6
• Sensory loss occurs across multiple nerve distributions 7

Diagnostic Approach

• The clinical and electrodiagnostic features of lumbosacral plexopathy and radiculopathy often overlap 1
• CT with IV contrast can be useful when MRI is contraindicated, offering the next highest level of anatomic visualization 5
• Electrodiagnostic examination helps confirm abnormalities in multiple nerve distributions 6

Common Pitfalls in Diagnosis

• Failure to distinguish between plexopathies and radiculopathies, which typically follow a single dermatome distribution 6
• Not recognizing that lateral disc herniations may cause plexopathy that is not detected on standard lumbar spine MRI 2

Management of Lumbosacral Plexopathy

Diagnostic Approach

• The American College of Radiology recommends MRI of the lumbosacral plexus as the primary diagnostic tool due to its superior soft-tissue contrast and ability to visualize intraneural anatomy in cases of nontraumatic lumbosacral plexopathy 8, 9
• MRI with and without IV contrast is recommended as it can detect and characterize various etiologies of lumbosacral plexopathy 9
• Imaging should be delayed approximately 1 month following trauma to allow for resolution of blood and soft-tissue edema 10
• Standard MRI of the pelvis without dedicated plexus imaging is not supported by evidence for evaluating lumbosacral plexopathy 9
• There is a significant correlation between nerve signal abnormality on MRI and findings of active radiculopathy on electromyography 9

Treatment Based on Etiology

• Penetrating and open injuries to the plexus often require early surgical exploration 10
• Blunt and closed injuries may be managed nonoperatively or surgically depending on the location and severity 10
• It is crucial to determine if a nerve is completely ruptured (requiring early operative management) or stretched but intact 10

Clinical Monitoring and Prognosis

• Approximately 71% of patients with lumbosacral plexopathy have a change in management resulting from MRI findings, highlighting the importance of accurate diagnosis 9

Common Pitfalls to Avoid

• Delaying appropriate imaging in traumatic cases; imaging should be performed approximately 1 month after injury 10

Management of Entrapment Neuropathy Causing Lumbosacral Plexopathy

Diagnostic Approach

• MRI of the lumbosacral plexus should include orthogonal views through the oblique planes of the plexus, with T1-weighted, T2-weighted, fat-saturated T2-weighted, or short tau inversion recovery sequences, and may include fat-saturated T1-weighted postcontrast sequences, as recommended by the American College of Radiology 11

Treatment Based on Etiology

Interventional Approaches

• Image-guided injections, such as botulinum toxin injections for piriformis syndrome when the sciatic nerve is compressed by the piriformis muscle, can be used as part of the treatment approach, according to the American College of Radiology 12

Surgical Management

• Surgical decompression is indicated when there is evidence of a structural lesion causing compression, such as a mass or fibrous band, and imaging shows this compression, as stated by the American College of Radiology 12

Common Pitfalls to Avoid

• Not recognizing that lateral disc herniations may cause plexopathy that is not detected on standard lumbar spine MRI, which is a common pitfall to avoid, as noted by the American College of Radiology 12

Extrinsic Tumor Compression of Peripheral Nerve Plexus

Neoplastic Causes

• Extrinsic tumors—such as lymphoma, sarcoma, and fibromatosis—can compress or infiltrate peripheral nerve plexuses, producing plexopathy, according to the American College of Radiology 13.

MR Neurography and Diagnostic Strategies for Pudendal Neuropathy

Imaging Protocol

• 3 Tesla MRI provides superior signal‑to‑noise ratio and spatial resolution compared with 1.5 Tesla for peripheral nerve imaging, improving visualization of the pudendal nerve. 14 – American College of Radiology
• A dedicated lumbosacral plexus MR neurography protocol (including diffusion‑weighted imaging) is required for accurate pudendal‑nerve assessment; standard pelvic MRI lacks the necessary sequences and coverage. 15 – American College of Radiology

Clinical Diagnosis

• Patients who report perineal sensory changes, sexual dysfunction that worsens with sitting, and a normal routine sensory exam fit the classic clinical pattern of pudendal neuropathy, which may be missed on routine examination. 16

Critical Pitfalls

• Do not order a standard “MRI pelvis” for suspected pudendal neuropathy because it lacks dedicated nerve‑imaging sequences and an optimized field‑of‑view. 15 – American College of Radiology
• Do not rely on a standard lumbar‑spine MRI to visualize the pudendal nerve; the nerve courses below the lumbosacral plexus within the pelvis and is not depicted on routine lumbar imaging. 15 – American College of Radiology

Complementary Diagnostic Studies

• Electrophysiological testing (pudendal‑nerve motor latency, evoked potentials, EMG of perineal muscles) can provide confirmatory evidence of peripheral neuropathy and demonstrate prolonged sacral latencies in diabetic or radiation‑induced pudendal neuropathy. 16