The cervical plexus is formed by the ventral rami of the first four spinal nerves (C1–C4), in a series of irregular loops. The plexus is situated close to the upper four vertebrae, between the deep anterior and lateral muscles of the neck, anterior to the middle scalene and deep to the sternocleidomastoid. Braches form cutaneous, muscular, and communicating nerves. The cutaneous branches (lesser occipital, great auricular, supraclavicular, and transverse cutaneous nerves of the neck) contain sensory information from the skin and soft tissues of the scalp and neck. The cervical plexus also provides motor innervation to several muscles including the diaphragm (via the phrenic nerve), sternocleidomastoid and trapezius (via the accessory nerve) and other deep cervical and hyoid muscles [9, 10]. There are also communicating branches to the accessory, hypoglossal, vagus, and sympathetic nerves [11].

Metastatic spread to cervical plexus typically occurs from neighboring tissue. Cancer may invade the plexus directly or indirectly via regional lymph nodes or bone (clavicle, first rib, or cervical vertebral bodies). Squamous cell carcinoma of the head and neck, lymphoma and adenocarcinoma of the lung and breast are the most commonly associated tumors [9].

Patients who develop metastatic disease in this area most commonly describe pain and stiffness in the neck, shoulder or throat. The pain is typically unrelenting and may worsen with coughing, swallowing and neck movement. General examination may be surprisingly normal or may demonstrate tender neck musculature unilaterally, palpable tumors or firm anterior or posterior cervical or supraclavicular lymph nodes. Patients often describe vague numbness, paresthesias, pressure, or burning; however, objective sensory loss may be difficult to identify. Additionally prior surgery in the area which can produce numbness in the skin of the anterior neck and submandibular area may complicate assessment of new sensory deficits. Clarifying the temporal relationship of symptom onset and surgery can help distinguish between these two etiologies [9].

Additional clinical manifestations depend on the area of the cervical plexus involved. Abnormality of the spinal accessory nerve or C3/4 roots may produce weakness of the trapezius. This typically manifests as shoulder weakness and scapular depression and winging, most notable with shoulder abduction. Phrenic involvement can present with an elevated and/or paralyzed hemi-diaphragm. Patients describe dyspnea, which is worse when supine. Unilateral weakness of the sternocleidomastoid, deep cervical, and hyoid muscles is typically asymptomatic. A history or exam suggestive of myelopathy raises the suspicion for epidural spread. Given the close proximity, manifestations of skull base, or brachial plexus involvement may also be present [9, 12].

EMG (Electromyography ) and NCS (nerve conduction studies ) are more limited in the assessment of involvement of the cervical plexus than the brachial or lumbosacral plexus but can add important information. In phrenic neuropathy, the phrenic CMAP (compound muscle action potential) may be abnormal and neurogenic changes may be seen on needle EMG of the diaphragm. In spinal accessory neuropathy, the CMAP of the spinal accessory nerve may be abnormal when recording from the trapezius and needle EMG of the trapezius and/or sternocleidomastoid may reveal neurogenic changes. These abnormalities in the phrenic nerve/diaphragm and spinal accessory nerve/trapezius can also be seen in a radiculopathy or segmental myelopathy affecting the C3/4/5 and C3/4 myotomes, respectively. Needle EMG of the upper and mid-cervical paraspinals can also reveal abnormal spontaneous activity suggestive of neurogenic abnormality. If metastatic disease is confined to the cervical plexus, routine median, ulnar and radial sensory, and motor responses should be normal [11].

The brachial plexus supplies the motor and sensory innervation of most of the upper limb. It is an arrangement of nerve fibers that runs from the spine (C5-T1 roots) through the neck, axilla, and into the arm. As the nerve fibers run proximally to distally, they are arranged into trunks, divisions, cords and individual nerve branches. The phrenic, dorsal scapular, and long thoracic nerve exit proximal to the plexus, off the nerve roots themselves and innervate the diaphragm, rhomboids and serratus anterior respectively. The ventral rami of the C5-T1 nerve roots then form three trunks: upper (C5/6), middle (C7) and lower (C8/T1). They are named with respect to their orientation to one another. They occupy a superficial position as they traverse the posterior cervical triangle. The lower trunk is adjacent to the lung apex and near the subclavian artery. Each trunk then divides into two divisions, anterior, and posterior. These divisions are retroclavicular and run between the middle third of the clavicle and the first rib. The three posterior divisions then form the posterior cord. The anterior divisions of the upper and middle trunk form the lateral cord and the anterior division of the lower trunk continues as the medial cord. The cords are named for their orientation to the axillary artery and are situated proximally in the axilla, next to the axillary lymph node chain. The posterior cord gives rise to the thoracodorsal nerve (latissimus dorsi), subscapular nerve (subscapularis), axillary nerve (deltoid), and radial nerve (triceps, brachioradialis, wrist, and finger extensors) and provides sensory supply to the posterior arm and forearm. The lateral cord divides into two branches: the musculocutaneous nerve and a branch, which joins a portion of the medial cord to form the median nerve. The rest of the medial cord forms the median and ulnar nerves and gives off the medial brachial cutaneous nerves of the arm and forearm, which supply sensation to the medial portion of the arm and forearm. The five terminal nerves of the upper extremity (musculocutaneous, axillary, median, ulnar, and radial) are distally situated in the axilla [11, 13].

Approximately 70% of tumors involving the brachial plexus come from either lung or breast. The remaining 30% percent arise from a combination of lymphoma, sarcoma, or others [8]. Most metastases to the brachial plexus involve the lower trunk or medial cord. Rarely, primary head or neck neoplasms grow inferiorly and invade the upper portions of the plexus. Sometimes plexus involvement is patchy. Neoplastic invasion of the plexus is rarely the earliest manifestation of cancer, except in Pancoast syndrome, which is typically caused by carcinoma at the apex of the lung invading the lower trunk/medical cord of the brachial plexus [11].

Pain is the most common presenting symptom of neoplastic brachial plexopathy. Typically, the pain originates in the shoulder or axilla and radiates along the medial arm and forearm and into the fourth and fifth digits and can be severe. In a large series, pain upon initial presentation was present in 75% of cases [8]. Sensory loss can follow the same distribution. Motor deficits most commonly (75%) affect the lower plexus. As such, patients will typically have weakness in intrinsic hand muscles, finger and wrist flexion and extension. Approximately one in five patients have an associated Horner’s syndrome due to involvement of the sympathetic trunk or ganglia near the first thoracic vertebrae. Given the proximity of this lesion to the spinal cord, a Horner’s syndrome should prompt a thorough evaluation for intraspinal disease [8].

Differential diagnosis of neoplastic brachial plexopathy depends on whether the patient has received radiation therapy (RT) . In patients who have received RT, the principal alternate diagnosis is radiation-induced brachial plexopathy. In patients who have received prior radiation and have a delayed brachial plexopathy, a radiation-induced nerve sheath tumor of the brachial plexus is also a consideration. This is much less common than radiation-induced brachial plexopathy and may develop 4–40 years after RT. Often presenting as a painful enlarging mass, these tumors are usually malignant. Radiation-induced arteritis may also be seen in patients with radiation-induced plexopathies. Chronic ischemic symptoms and signs can present in the arm and hand or they may have episodic discoloration in the fingers from emboli. This may appear similar to atherosclerotic disease on arteriography. In a patient with known malignancy who has not undergone radiation to the upper chest, the main alternate diagnoses are perioperative brachial plexus trauma or an unrelated episode of acute brachial plexus neuropathy. Primary tumors of the brachial plexus are rare. Most are benign peripheral nerve sheath tumors, including neurofibromas and benign schwannomas [11].

The lumbosacral plexus is derived from the ventral rami of the L1-S4 nerve roots and is made up of two sections. The upper portion is the lumbar plexus, which arises from the L1–L4 nerves roots with variable contribution from T12. The lower portion is the lumbosacral plexus, which arises from the L4-S4 nerve roots. The lumbosacral plexus lies within the psoas major muscle and exits from the lateral edge of the muscle. In general, the lumbosacral plexus supplies motor and sensory functions to the ipsilateral leg and pelvic girdle. The upper portion of the plexus gives rise to several major nerves: the iliohypogastric nerve (T12-L1), the ilioinguinal nerve (L1), the genitofemoral nerve (L1–2), the lateral femoral cutaneous nerve (L2–4), and the obturator nerve (L2–4). Major motor functions include hip flexion and adduction, and knee extension. The upper plexus supplies sensation to the groin, thigh (anterior, lateral, medial), and the medial portion of the leg. The lower portion of the plexus also gives rise to several major nerves: superior gluteal nerve (L4-S1), the inferior gluteal nerve (L5-S2), the sciatic nerve (L4-S3, consisting of the tibial and peroneal components), the posterior femoral cutaneous nerve (S1–S3), and the pudendal nerve. Major motor functions include hip abduction, hip extension, knee flexion, ankle movements, and control of the urinary and anal sphincters. It provides sensory function from the lower extremity distal to the knee (except the medial lower leg), posterior thigh, buttocks, and perineal region [14].

Metastatic lumbosacral plexopathy occurs most commonly from direct extension of abdominal and pelvic tumors. Occasionally, however, the plexus is affected by growth from metastases to regional lymph nodes or bony structures. Colorectal cancer is the most common primary tumor. Colorectal cancer along with retroperitoneal sarcoma and breast cancer account for almost half the cases. Lymphoma, cervical cancer, and other malignancies account for the remaining cases. In approximately 15% of patients, plexopathy is part of the initial presentation of cancer. Tumor can either directly invade the plexus or can track along connective tissue or epineurium. When tumor cells track, the presence of cancer can be difficult to demonstrate on imaging. Metastatic plexopathy is typically unilateral, but is bilateral in 25% of patients [9].

Metastatic lumbosacral plexopathy begins with leg pain in nearly all patients, which is followed by numbness and weakness. In a series of 85 patients, pain was so common during the course (98%) and at presentation (91%), that the authors indicated its absence should prompt consideration of alternate diagnoses [7]. Like with brachial plexopathy, the pain is typically constant, dull and aching. Sharp, radicular pain often coexists. Valsalva may exacerbate pain. Patients describe difficulty finding a comfortable position but lying supine may be particularly uncomfortable. Lying with hips flexed can relieve the pain if there is involvement of the iliopsoas [7].

Weakness and sensory disturbance develops in the majority of patients. Leg weakness (86%), sensory loss (73%), reflex loss (64%), and leg edema (47%) are the most common presenting features. A rectal mass may also be present. The distribution of numbness or weakness depends on which part of the plexus is affected. In this same series of 85 patients, the upper plexus (L1–4) was involved in 31% of patients, and the lower plexus (L5-S3) in 51%, while 18% had a pan-plexopathy [7]. In colorectal neoplasms and cervical carcinoma, the sacral plexus is most commonly involved. Accordingly, these patients typically have pain in the posterior thigh, leg or calf and weakness of ankle plantar flexion and knee flexion. Sensory disturbance may involve the posterior leg and sole of the foot [7]. Approximately 20–30% of patients describe a unilateral “hot dry foot.” The foot is objectively warm and has hypohydrosis. This is a manifestation of interruption of sympathetic ganglia or postganglionic fibers along the lumbosacral plexus or the peripheral nerves below the L3 segment. This can be an important localizing feature. Autonomic disturbances are not present with lesions of the nerve roots or cauda equina. These autonomic symptoms may precede the onset of weakness or numbness by several months or occur simultaneously [15]. When the upper plexus is involved, patients typically experience pain and sensory changes in the anterior thigh, groin and into the dorsum of the foot. Sarcoma is the most common neoplasm to present in this fashion. Loss of strength affects thigh muscles producing difficulty arising from a low-seated position or walking down stairs. Involvement of the lumbosacral trunk can produce foot drop, which is distinguished from a peroneal neuropathy by weakness of ankle inversion. Incontinence and impotence may be present, typically with bilateral plexus involvement. Pan-plexopathies, most commonly caused by genitourinary malignancies, can cause a combination of these findings [7, 9].