Clinical Imaging Of The Bp


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Clinical Imaging Of The Bp

  1. 1. CLINICAL IMAGING OF THE BRACHIAL PLEXUS:Himadri S. Das, N. Medhi, P. K. Sharma, P. Goswami, P. Hazarika, B. J. SharmaPrimus Imaging, GuwahatiThe Brachial Plexus (BP) is comprised of the roots, trunks, divisions, cords, and branches.ANATOMYThe brachial plexus originates from the anterior divisions of the spinal nerve roots of C5-T1.Variations in innervation are occasionally present. A “pre-fixed” BP occurs when C4 replacesT1 as a dominant contributor. A “post-fixed plexus is present when BP receives contributionsfrom C6 – T2. These variations appear to have little clinical significance.The BP is formed in the majority by the anterior divisions of the spinal nerves of C5 – T1 thatforms its roots. The roots of the BP then combine to form the 3 trunks (upper, middle, lower).The roots of C5 and C6 combine to form the upper trunk, while the roots of C8 / T1 combine toform the lower trunk. The C7 root is the sole contributor of the middle trunk.The trunks of the BP then split into anterior and posterior divisions. These divisions combine toform the cords of the BP. The cords of the BP are named (posterior, lateral, medial) accordingto their relationship with the adjacent subclavian artery. The posterior divisions of the upper,middle and lower trunk combine to form the posterior cord. The anterior divisions of the upperand middle trunks combine to form the lateral cord, and the anterior division of the lower trunkcontinues to form the medial cord.The BP terminates in various branches, which supply motor sensory innervation to the upperextremity. The suprascapular nerve is the only terminal branch that originates from a trunk ofthe BP. FIG1: ANATOMY OF THE BP
  2. 2. PERIPHERAL NERVES THAT ORIGINATE FROM CORDS OF THE BRACHIAL PLEXUSBranches from the lateral cord Lateral pectoral nerve Musculocutaneous never Lateral head of the median nerveBranches from the median cord Medial pectoral nerve Medial cutaneous nerve of the upper arm Medial cutaneous nerve of the forearm Medial root of the median nerveBranches from the posterior cord Upper subscapular nerve Thoracodorsal nerve Lower subscapular nerve Axillary nerve Radial nerve SURGICAL ANATOMYThe surgical classification is based on the relationship of the BP to the clavicle and divides itinto supraclavicular, retroclavicular, and infraclavicular segments. The supraclavicular BPcontains the roots and trunks and is situated in the posterior triangle between the anterior andmiddle scalene muscles.The retroclavicular plexus contains the divisions and is located posterior to the clavicleadjacent to the subclavian artery. The infraclavicular plexus also courses adjacent to thesubclavian artery and contains the cords and portions of the distal branches of the BP.RADIOGRAPHIC ANATOMYThe radiologist can identify specific portions of the BP based on certain anatomic structures,which are easily seen on imaging studies. The fascial plane between the anterior and middlescalene muscles contains the roots and cords of the BP. The divisions and cords courseadjacent to the subclavian artery. Thus, any mass that is adjacent to the subclavian artery is inclose proximity to the divisions and cords of the BP. The branches of the BP are difficult toidentify individually on imaging studies. However, it may be safely assumed that a mass in theaxillary region is likely to involve the terminal branches of the cords. FIG 2(a): CORONAL T1 WEIGHTED MR SEQUENCE
  3. 3. FIG 2(b): AXIAL T1 WEIGHTED MR SEQUENCEAbbreviations: Clavicles (C), subclavius muscles (SUB), external jugular vein (XJ), internaljugular vein (J), subclavian veins (SV), axillosubclavian veins (AXV), coracoid processes (CP),brachiocephalic artery (BR), first ribs (FR), trachea (T), right lung (RL), and left lung (LL) arelabelled for reference. The aorta (A) and pulmonary artery (P) are labeled to identify the heart.CLINICAL SCENARIO:Clinical features of a brachial plexopathies are often vague and non-specific. Symptomsinclude motor, sensory and sometimes, autonomic disturbances of the supraclavicular region,shoulder, and upper extremity. Motor weakness is primarily seen in those patients withobstetric-related palsies and avulsions of anterior roots. Sensory deficits are more often relatedto those patients with neoplastic and/or radiation induced plexopathies. Neoplasticplexopathies tend to be more painful and progress more rapidly than radiation-induced ones.Long-term complications resulting from brachial plexopathies include muscle wasting, upperextremity edema, osteoporosis, joint contractures, complex regional pain syndromes and/orsympathetically mediated pain, and joint degeneration.There are certain clinical findings that help to localize the inciting lesion and thus permitradiologists to focus their diagnostic evaluation. The phrenic nerve receives contributions fromC3 – C5. Because of this overlap in innervation with the upper roots of the BP, a plexopathyassociated with a paralyzed diaphragm indicates involvement of the upper plexus. Therhomboid and serratus anterior muscles are innervated by proximal branches of the BP (C5 –C7). Thus, rhomboid muscle paralysis or winging of the scapula is indicative of a proximalinjury.The Erb-Duchene palsy is most often a consequence of birth injury which results from shoulderdystocia during a vertex vaginal delivery. Obstetrical palsies tend to occur more often in largerbabies, breech or forceps deliveries, and after prolonged labors. The right shoulder is morecommonly affected because the head is usually in a left occiput anterior position. Excessivetraction on the head and neck results in an injury limited to the C5 and C6 nerve roots. Patientswith an Erb’s palsy have characteristic physical findings which consist of adduction and internalrotation of the arm with pronation of the forearm.Several associated clinical findings implicate a lower BP lesion. The stellate ganglion receivescontributions from C8-T1. Thus, a brachial plexopathy associated with an ipsilateral Horner’ssyndrome is indicative of a lesion involving the lower BP. The classic Dejerine-Klumpke palsyis due to a failure to deliver the upper extremities before the head during a breech vaginaldelivery. Forcible abduction of the arms causes excessive stretching and results in an injury tothe nerve roots of C7-T1. This injury involves the lower intrinsic hand muscles, and the radial
  4. 4. innervated extensors. Such an injury characteristically results in a paralysed (“claw”) hand.Because of the overlap in innervation with the stellate ganglion, Klumpke’s palsy may also beassociated with ipsilateral Horner’s syndrome.Several findings may be indicative of a more severe injury to the BP. A plexopathy associatedfindings similar to a Brown-Sequard syndrome may suggest a proximal nerve root avulsion andspinal cord injury. A nail limb with complete absence of deep tendon reflexes is indicative of acomplete disruption of the BP.INDICATIONS OF MR IMAGING: 1. Are symptoms unilateral or bilateral? The presence of bilateral brachial plexopathies is usually associated with a lesion in the epidural space or neural foramina, and these patients should be evaluated initially with a dedicated imaging study of the cervical spine. 2. Is there a history of trauma? These patients often require dedicated sectional imaging studies of the cervical spine to supplement the evaluation of the peripheral components of the plexus. 3. Is there an associated mass in the neck, supraclavicular fossa or axilla? Characterization of a palpable mass may require the use of double-echo-T2-weighted rather than SE-T2 weighted sequence and the administration of intravenous contrast. 4. Are the symptoms produced by a particular arm position? Hand pain with arm elevation of a common finding with thoracic outlet syndrome secondary to a cervical rib, and identification of a cervical rib on a frontal radiograph should prompt further evaluation of the subclavian and axillary arteries rather than the soft-tissue components of the brachial plexus. 5. Does the patient have a prior history of carcinoma? Studies of patients with a history of malignancy require a careful search for abnormal signal within the trabecular bone of the cervical spine, clavicle, scapula, and shoulder as well as the soft tissues adjacent to the nerves. This is especially important if pain is the only presenting symptom. 6. Is there a history os surgery or radiation therapy to the affected axilla, neck or supraclavicular fossa? Images of the affected side in these patient are often confusing and oblique coronal and sagittal imaging of the opposite brachial plexus is often useful for comparison and identification of subtle changes.IMAGING IN VARIOUS PATHOLOGIES OF THE BRACHIAL PLEXUS:TRAUMAThe initial imaging evaluation in patients with a post-traumatic brachial plexopathy shouldconsist of plain films of the cervical spine, shoulder, clavicle and chest. These plain filmsshould be assesses for fractures of subluxations which could account for the acuteneurological deficit.Posttraumatic nerve root avulsion of the BP results from forcible trauma which separates thearm from the shoulder. This may result in stretching and tearing of fibrous attachments whichextends from the nerves to their respective transverse processes. Pseudomeningoceles arisefrom tears of the dura and arachnoid membranes caused by the root sleeves being pulled outinto the intervertebral foramen. Nerve root avulsion results if the traction force exceeds theelastic tolerance of the root. Spinal cord injury may occur from direct contusion or by avulsionof the nerve root. Thus, it is possible to have post-traumatic Pseudomeningoceles without acoexistent nerve root avulsion. Conversely, approximately 20% of clinical nerve root avulsionsare not associated with a pseudomeningocele.Both CT Myelography and MR imaging may be used to evaluate patients with post-traumaticbrachial plexopathies. The characteristic findings in a posttraumatic BP stretch injury are
  5. 5. Pseudomeningoceles which may be detected by both CT Myelography and MR imaging. Thinsection CT Myelography (1mm-3mm thick sections) allows for consistent visualization of theventral and dorsal nerve roots within the spinal canal and is therefore the preferred imagingmodality.Absence of a nerve root shadow on CT Myelography is indicative of nerve root avulsion. Nerveroot or dural thickening seen on MR imaging is suggestive of nerve root avulsion or edema.Recent technical advances in MR imaging permit improved visualization of the nerve rootswithin the spinal canal in normal patients, however, these advanced techniques are mostlylimited to tertiary institutions and are not currently in general use. MR imaging does allowvisualization of Pseudomeningoceles , which do not fit with contrast on CT Myelography. Therole of MR Myelography for evaluating BP injuries is currently being evaluated.Other post-traumatic lesions which may result in a brachial plexopathy include hematomas,vascular compression from pseudoaneurysm formation, and complete disruption of thebrachial plexus. The presence of intramedullary or extramedullary haematoma may bedetected with MR imaging. MR imaging is superior to CT for evaluating for the presence andextent of soft tissue injuries.FIG 3: CORONAL T2 W IMAGE SHOWING POST TRAUMATIC PSEUDOMENINGOCELETRAUMATIC CAUSES OF BRACHIAL PLEXOPATHYFractures of the cervical spine or clavicleNerve root avulsion with or without an associated pseudomeningoceleSoft tissue edemaHematomaNONTRAUMATIC CAUSES OF BRACHIAL PLEXOPATHYPrimary neural tumors such as meningioma and schwannomasMetastatic diseasePan coast tumorPost irradiation injuryRadiculopathy secondary to disk diseaseBony abnormalities such as cervical rib.NEOPLASM’S
  6. 6. A variety of neoplasms may involve the BP. These lesions may be classified as tumours ofneural (primary) and of non-neural origin (secondary). Primary BP tumors most commonlyarise from the nerve sheaths. The most common benign neural tumors are neurofibromas andschwannomas. Neurofibromas are the most common neural tumor to involve the BP.Histologically; these lesions are unencapsulated tumors that are felt to arise from the nervefascicles. One-third of these lesions occur in patients with Neurofibromatosis type 1 (NF-1)while two- thirds of cases are sporadic. Neurofibromas arising in patients with NF –1 occur withequal incidence in males and females. These tumors are characteristically multiple andplexiform in appearance with diffuse involvement of the BP. In contrast, sporadicneurofibromas are more commonly seen in females (2-3:1 female to male ratio). Sporadicneurofibromas are typically solitary and most likely originate in the supraclavicular BP.Schwannomas are the second most common neural tumor involving the BP.The imaging features of solitary neurofibromas are essentially indistinguishable from those ofthe schwannomas. On CT, these lesions have similar attenuation to muscle and enhancevariably with contrast. Both tumors may be associated with bony remodeling. On MR imaging,these two lesions are isointense to muscle on T1W sequences and hyperintense on T2Wsequences. Both tumors typically enhance following intravenous Gadolinium administration.The diagnosis of neurofibromas may be made with a high degree of confidence if the lesionshave a plexiform appearance or occur in a patient with NF-1.Malignant neural tumors are very rare and consist mostly of fibro sarcomas and neurogenicsarcomas (malignant neurofibromas). Secondary neoplasms may extend to involve theadjacent BP. These lesions may also be either benign or malignant. Benign masses whichinvolve the BP include: lipoma, lipoblastoma, desmoid, lymphangioma, myoblastoma,osteochondroma, and ganglioneuroma.Malignant neoplasms which may involve the BP are commonly due to direct extension from aPancoast tumor or metastatic disease. Involvement of the BP by direct extension of aPancoast tumor may be suspected in patients who present with supraclavicular pain,weakness and paresthesias. Imaging findings suggestive of BP invasion by a superior sulcustumor are obliteration of the apical fat and proximity of the mass to the BP. Tumors which havebeen reported to metastasize to the BP include breast, lymphoma, bladder, gastrointestinal,testicular, thyroid, lung, melanoma, head and neck, and sarcomas.The imaging modality of choice in patients with possible neoplastic invasion of the BP is MRimaging due to its multiplanar capability and high soft tissue characterization. Previous studieshave shown MRI to have a high sensitivity (100%) in detecting neoplastic involvement of theBP. The extent of disease is also better depicted with MRI than with CT. Coronal T1W imagesare especially helpful for assessing the status of the apical fat in patients with Pancoast tumorsand evaluating the relationship of masses to the BP.INFLAMMATORYInflammatory processes may involve the BP include radiation therapy, neuritis, and infections.Radiation therapy (RT) may injure the BP and cause a plexopathy. Three classical syndromesof RT induced brachial plexopathy have been described. The most common form is a delayedprogressive radiation fibrosis. The remaining two forms of radiation damage are a reversible ortransient plexopathy and an acute ischemic plexopathy.Radiation- induced brachial plexopathy is the most common and severe peripheral nervoussystem complication of RT. Radiation damage to the BP appears to be dose related and mostlikely occurs in patients who have received doses in excess of 6000 cgys. It is most commonlyseen in females who have been treated with RT for breast cancer. The plexopathy tends to bedelayed and progressive with the majority of patients presenting atleast 6 months after thecompletion of RT. The initial symptoms include paresthesias, followd by pain and weakness.These symptoms typically occur in upper trunk distribution with weakness of the arm flexorsand shoulder abduction. Pain can accompany these paresthesias but it usually occurs late in
  7. 7. the course of this syndrome. However, other reports suggest that RT induced plexopathies aregeneralized and that the distribution of the deficits is not helpful in separating this variety ofplexopathy from a neoplastic one. Histologically in RT –induced plexopathy, there is densefibrous tissue encasing the BP with Wallerian degeneration. On physical examination,radiation- induced brachial plexopathy may result in reflex abnormalities, intrinsic muscleweakness, muscle atrophy and lymphedema.MRI is the modality of choice for evaluating patients previously treated with RT to thesupraclavicular region. The imaging findings of RT –induced brachial plexopathy are diffusethickening and enhancement of the BP without a focal mass. The presence of a focal mass ina patient treated with RT is suspicious for recurrent tumor and requires further evaluation,especially in patients treated with doses less than 6000 cgys. Horner’s syndrome is rarelycaused by RT alone and, when present, is also strongly suggestive of recurrent tumor.Active inflammation of the BP is termed “brachial neuritis” (BN). Its etiology may be due to aprimary viral infection (cytomegalovirus, coxsackie), or complication from prior infection. BNmay also result as a complication of previous serum vaccine, antibiotic, or other drugadministration. Idiopathic and heredofamilial forms of BN have also been described. Patientswith BN typically present between the third to seventh decades of life. The condition is slightlymore common in males than in females (2.4::1). Clinically, these patients present with an achein the supraclavicular region and shoulder. The pain often worsens over a 3-10 day period andmay be followed by weakness and sensory and reflex impairment. In most cases, the diseaseis self limited and subsides over a 6 to 12 week period. However, residual deficits occur insome patients. MRI is the modality of choice in patients suspected of having BN. The MRIfindings are diffuse thickening, abnormal T2W signal intensity, and abnormal enhancement ofthe BP on the gadolinium enhanced images.Infectious processes involving the BP most commonly involve its supraganglionic portion andare most likely due to discitis with associated epidural abscesses. Involvement of the moredistal components of the BP is unusual and may be due to extension from and adjacentinfection.MISCELLANEOUSThe clinical symptoms of degenerative cervical disc disease may mimic those of a brachialplexopathy; therefore, evaluation of the cervical spine should be included in imaging studies ofthe BP. Eighty to ninety percent of cervical radiculopathies involve the C6 (C5/C6 disc) and C7(C6/C7 disc) roots. Patients may present with numbness, pain, sensory loss, and diminishedreflexes at the affected levels. These symptoms may be exacerbated by coughing, sneezing,or lateral head movements.Brachial plexopathy may also be caused by cervical ribs. Cervical ribs are present inapproximately 1% of the population and are symptomatic in 10% of affected individuals. Theyare more common in females than in males (2:1) and are unilateral in 50% - 80% ofindividuals. Occasionally, a cervical rib may be attached to the first rib by a fibrous band. TheBP may be affected by cervical ribs in one of two ways. The cervical rib may be positioned sothat the BP must cross over it to enter the axilla, thereby stretching the lower trunk. Secondly,the cervical rib may narrow the space between the posterior aspect of the first rib and theanterior scalene muscle reducing the area through which the BP and subclavian artery course.The cervical rib syndrome is felt to result from compression of the lower trunk of the BP as itcrosses over the cervical rib or by compression of the lower trunk by a fibrous band thatattaches to the first rib. The symptoms consist of pain and /or paresthesias along the ulnarborder of the forearm and hand and motor weakness in a similar distribution. Continuedcompression may result in muscle wasting which initially involves the thenar eminence but mayalso spread to involve the small muscles of the hand.REFERENCES :
  8. 8. 1. Som P.M, Curtin H. Head & Neck Imaging, 4th edition, 1998, Mosby Inc, Volume-II, Mosby Inc, page no 22217-22252. Mukherji SK, Castillo M, Wagle A. Brachial Plexus. Seminars in CT, US and MR imaging 1996; 17:5193. Posniak HV, Olson MC, Dudiak CM, Wisniewski R, O’Malley C. MR imaging of the Brachial Plexus. AJR 1993; 161:373-3794. Guha A, Graham B, Kline DG, Hudson AR. Brachial Plexus injuries. In: Wilkins RH, Rengachary SS, Eds. Neurosurgery 2nd ed. New York, NY: McGraw-Hill 1996:3121- 31345. England JD, Summer AJ. Nontraumatic Brachial plexopathy. In: Wilkins RH, Rengachary SS, eds. Neurosurgery 2nd ed. New York, NY: McGraw-Hill 1996:3245-32506. Davies ER, Sutton D, Bligh AS. Myelography in brachial plexus injury. Br J Radiol 1966; 362-3717. El-Gammel T, Brooks BS, Freedy RM, Crews CC. MR Myelography: imaging findings. AJR 1995; 164:173-1778. Bowen BC, Verma A, Brandon AH, Fiedler JA. Radiation induced brachial plexopathy: MR imaging with clinical correlation AJNR 1996; 17:1932-1936