Anatomy Magnetic Resonance Imaging - Essay Example

Anatomy Magnetic Resonance Imaging Anatomy Magnetic Resonance Imaging Anatomy of Elbow joint Elbow joint is a complex synovial joint. It is formed of combined articulation of Humerus, ulna and radius bones of upper extremity along with joint capsule and pair of ligaments to provide strength and stability. Elbow offers wide range of movements such as flexion, extension, pronation and supination. Morphology Elbow joint comprises of distal end of Humerus which consists of trochlea and capitellum that articulate with the proximal end of Ulna and head of Radius respectively to form hinge. Radius also articulates with Ulna at the radial notch forming a pivotal joint. Bony articulation is well protected by joint capsule (Wessely et al, 2006, pp.201-205). MR anatomy of elbow Curtsey: (Spina, p.30). There are mainly two ligaments on either side condensed with the joint capsule. They are ulnar co-lateral ligament and radial co-lateral ligament. Ligaments support the join by adding strength to the joint (Wessely et al, 2006, pp.201-205). Muscles surrounding elbow are Biceps Brachii and Brachialis on anterior side whereas posterior side is covered with Triceps Brachii and Anconeus. On medial side, there are Pronator Teres, Palmaris longus and the group of Flexor digitorum superficialis,Profoundus, Flexor carpi radialis and Ulnaris and lastly flexor pollicis longus and on lateral side, Supinator and Brachioradialis along with the group of extensor muscles of hand and wrist (Wessely et al, 2006, pp.201-205). Nerve and vascular supply There are three major nerves passing through elbow joint. Those are median nerve, Radial nerve and ulnar nerve. Ulnar nerve lies superficially and is commonly injured due to its superficial placement whereas radial and median nerves lie deep in the fossa. Brachial artery passes through the cubital fossa and it is located over Brachialis muscle. This artery further divides into Ulnar and Radial artery (Wessely et al, 2006, pp.201-205). MRI of the elbow-Different patient positions While MRI elbow is examined, patient and his affected arm are arranged in such a manner to achieve maximum visualization and accurate diagnosis. Some factors do have influence over patient’s arrangement such as disease pathology and restricted hand movements; limitation of existing MRI machine, patient’s age etc. Here is the brief comparison of two common positions tried during elbow MRI, Patient supine with elbow extended- Patient is asked to lie down in supine position with arm extended and wrist straight. Circular coil is placed underneath the elbow for high intensity resolution. This position is not only suitable to all the patient but also helps to achieve T1 weighted images on coronal plane but “Short time inversion recovery” (STIR) sequence is often affected due to “suppression of fat” resulting in poor signal output (Spina, p.29). Patient prone with arm extended overhead-Patient is in prone position with the arm extending upward, as seen in the picture 2. Cylindrical coil has been used which enables better quality imaging. This is the most recommended position for the patients who are not comfortable in dark conditions but highly unsuitable gesture for many others. So, in order to avoid motion artifact, imaging needs to be done rapidly (Spina, p.29). MRI elbow-Comparison of the artifacts It is vital to understand common artifacts that are routinely encountered during MRI elbow procedure. These errors are common with different MRI techniques. In order to have accurate diagnosis, artifact needs to be minimized. Here are some of the common artifacts of MRI elbow procedure: Motion artifact Aliasing artifact or wraparound artifact Chemical shift artifact Susceptibility artifact. (Anderson, 2011, pp 5-6) Aliasing or wraparound artifact is most commonly encountered during sideways elbow positioning. This is due to the focused object is greater than the field of visualization. In such case “phase encoding” is not permissible as this result in low sampling rate. In order to overcome this artifact “phase oversampling” is needed. When the elbow is placed over the head aliasing is not a problem (Anderson, 2011, pp 5-6). According to Pusey et al (1986, pp.892-908), chemical shift artefact is another major artefact and usually come across when the frequency encoding axis remains as high or low bandwidth on either side of the body area which is high in fat .This artefact is noted in high intensity fields and this is resolved by changing either axis of the patient or pulse sequence. Otherwise, reduction in intensity of the surrounding magnetic field is necessary. (Anderson, 2011, pp 5-6) Calcifying tendonitis of the rotator cuff Calcified tendonitis is a condition wherein there is deposition of calcium crystals in the tendons of rotator cuff. Rotator cuff is a protective layer of the shoulder joint offering maximum strength. Calcific tendonitis occurs at the later age of the life and predominantly seen in females. Patient experiences intermittent severe pain in chronic conditions. Clinical features Patient often complaints of chronic dull ache around the shoulder. Pain is usually nocturnal causing restlessness. Sudden hikes of pain are also noticed restricting movements at the joint. Pain can also be radiating in upward or downward direction. (Gosens & Hofstee, 2009). Causation and progress Calcified Tendonitis is characterized by accumulation of calcium hydroxyapatite crystals. Common site for deposition of crystals is Supraspinatous tendon (51%-91%) with lesser incidences in Infraspinatous, Subscapularis tendons hardly up to 3%. (Gosens & Hofstee, 2009). Exact etiology is uncertain though repetitive trauma could be one of the inducing factors. Altered blood supply over the period leads to degenerative changes resulting in initial fibrosis and subsequently necrotic changes in the tendon. This degenerative process takes place through following steps (Gosens & Hofstee, 2009).They are, 1) Precalcific phase- indicates metaplastic growth inside the cartilaginous tissue. 2) Formative phase- includes formation of calcified structure within the metaplastic growth. 3) Resorptive phase- Calcified elements reabsorbed within the cell structures 4) Healing phase- This is a natural process of repair by tendon itself where crystals are degenerated. When this process gets blocked at some level, it results in chronic condition. Lab findings-x ray and MRI Calcified deposits are best viewed on x ray shoulder. AP view is recommended with internal and external rotation of shoulder joint. Lateral view is also helpful. Crystals are classified as per their appearance on the film. This classification is on the basis of French Arthroscopic society. This appearance of the crystals on x ray certainly helps for knowing the stage of the disease (Gosens & Hofstee (2009) : Type A- Crystals are sharp, delineated and homogenous. Type B- Sharp, dense but fragmented. Type C- Heterogeneous appearance, fluffy. Type D- Dystrophic calcification Type A and B are suggestive of chronic condition where natural recycling mechanism is altered. Type C and D are indicative of Resorptive phase of the cycle which suggests good prognosis (Gosens & Hofstee, 2009). MRI is not indicated in all the cases as X ray is conclusive and cost effective too. Calcified crystals are well appreciated on MRI only when they are bigger in size and surrounded by infiltration. MRI is advised when severe damage to the tendon is suspected and often compared with x ray results (Gosens & Hofstee (2009). About carpal bones Carpal bones are also known as wrist bones. They are eight in each hand. They articulate with distal ends of Radius and Ulna and metacarpals. They are coined as Trapezium, Trapezoid, Capitate, Hamate, Triquetrum, Scaphoid, Pisiform, and Lunate. They can be seen in the picture below. Ganglion in brief Ganglion is defined as “a cystic, tumour-like lesion of unknown origin, which is surrounded by dense connective tissue filled with gelatinous fluid rich in hyaluronic acid and other mucopolysaccharides” (Beaman & Peterson, 2007, pp 972-974). Ganglions are commonly spotted around wrist and knee. They are mostly asymptomatic and disappear without any intervention. They are often accidently noted during scans. There is no distinct aetiology for the formation of ganglion but they are often found at the area exposed to excessive friction such as wrist. (Beaman & Peterson, 2007, pp 972-974) Ganglion on MRI Ganglions appear like a rounded cystic lesion unilocular or multilocaular on MRI plate in T1 and T2 images along with well defined internal septal lining. Chronic cases will have slightly complicated appearance as the cyst might have filled with haemorrhagic or high proteinaecous content. Sometimes it gets difficult to differentiate them from synovial cyst on MRI and further details are required for confirmation. Ganglion could also be classified depending upon their MRI appearance. Periosteal ganglion appears as distorted cortex due to external pressure whereas ACL ganglion appears fusiform in shape (Beaman & Peterson, 2007, pp 972-974). Carpal tunnel syndrome Carpel tunnel syndrome is a result of median nerve compression in the carpel tunnel resulting in tingling numbness, weakness in the hand etc. Incidence is higher in females above the age of 45. This syndrome is also noted in athletes and weight lifters who are exposed to repetitive wrist movements and heavy weight lifting (Hui, Wong & Griffith, 2005, pp 210-213). Etiological factors Anything that reduces the gap of the carpel tunnel and induces pressure on median nerve results in carpel tunnel syndrome such as any Mechanical trauma or fracture Inflammation of the joint, e.g. Arthritis of wrist Infection Malignancy Obesity Pressure from surrounding structures Congenital narrowing of the carpel tunnel. (Hui, Wong & Griffith, 2005, pp 210-213). Clinical features Patient with carpel tunnel syndrome typically presents symptoms of tingling sensation with numbness in hand. Complaints worsen during night driving patient restless. In advanced cases, patient feels weakness and loss of grip in the affected hand. Syndrome also has atypical presentation of thenar weakness, dryness of palms, fingers swelling with stiffness (Hui, Wong & Griffith, 2005, pp 210-213). Axial view-arrow pointing normal median nerve in the carpel tunnel Curtsey- (Hui, Wong & Griffith, J. (2005), p214). Diagnosis with MRI In order to diagnose median nerve compression, Nerve conduction test is the method of choice. Ultra Sonography is also quite helpful to determine status of nerve compression and it is cost effective than MRI. MRI helps to distinguish status of every structure of carpel tunnel along with exact location of median nerve. It is also immensely helpful in case of anatomical variations of median nerve (Steinbach & Smith, 2000, pp.313-314; Hui, Wong & Griffith, 2005, pp 210-213). MRI is also mandatory in certain conditions when: Electromyography does not support the clinical findings. Malignancy suspected Infiltrative cases Prior to repair operation to determine the location of median nerve Post operative –when the symptoms still persist, to rule out unknown causes of median nerve affections (Steinbach & Smith, 2000, pp.313-314; Hui, Wong & Griffith, 2005, pp 210-213). References Anderson, M. (2011). ACR–SPR–SSR Practice Guideline for the Performance and Interpretation of Magnetic Resonance Imaging (MRI) of the elbow. [online] Available from http://www.acr.org/SecondaryMainMenuCategories/quality_safety/guidelines/dx/musc/mri_elbow.aspx [Accessed: Mar 26, 2012]. Beaman, F.D. & Peterson, J.J. (2007). MR Imaging of Cysts, Ganglia, and Bursae about the Knee. Radiologic Clinics of North America, vol. 45, no., pp. 972-974. [online] Available from: http://www.med.nyu.edu/pmr/residency/resources/Radiology/Rads%20clinics_MRI%20knee%20cysts%20ganglis%20bursae.pdf [Accessed: Mar 28, 2012] Gosens, T. & Hofstee, D.J. (2009). Calcifying Tendinitis of the Shoulder: Advances in Imaging and Management. Current Rheumatology Reports, vol. 11, no. pp. 129-134. Hui, A.C., Wong, S.M. & Griffith, J. (2005). Carpal tunnel syndrome. Practical Neurology, vol. 5, no. pp. 210-213. Pusey, E., Lufkin, R.B. & Brown, R.K. (1986). Magnetic resonance imaging artifact: Mechanism and clinical significance. Radiographics, 6(5). [online] Available from http://radiographics.rsna.org/content/6/5/891.full.pdf [Accessed: March 26, 2012]. Spina, V. & Baldini, L. Imaging of the Elbow. Vol. Chapter 3, no. pp. 28-29. Steinbach, L. & Smith, D. (2000). MRI of the wrist. Journal of Clinical Imaging, vol. 24. Pp.313-314. Wessely, M.A., Hurtgen-Grace, K.L. & Grenier, J.M. (2006). Elbow MRI Part 1. Normal imaging appearance of the elbow. Clinical Chiropractic, vol. 9, no. pp. 198-205. Diagrams 1) MR anatomy of elbow Spina, V. & Baldini, L. Imaging of the Elbow. Vol. Chapter 3, no. pp. 30. 2) Patient supine with elbow extension Spina, V. & Baldini, L. Imaging of the Elbow. Vol. Chapter 3, no. pp. 29. 3) 2. Patient is prone with arm extended overhead Spina, V. & Baldini, L. Imaging of the Elbow. Vol. Chapter 3, no. pp. 29. 4) Carpal bones http://www.bartleby.com/107/illus336.html 5) Ganglion http://medicalpicturesinfo.com/?s=ganglion 6) Axial view-arrow pointing normal median nerve in the carpel tunnel Hui, A.C., Wong, S.M. & Griffith, J. (2005). Carpal tunnel syndrome. Practical Neurology, vol. 5, no. pp. 214. Read More