Differential diagnosis of acute calf pain and swelling with emergency ultrasound

Transcription

1 Hong Kong Journal of Emergency Medicine Differential diagnosis of acute calf pain and swelling with emergency ultrasound KL Chung, KY Cheung, CW Kam Acute calf pain and swelling are common causes of emergency department attendance. Differential diagnoses may mimic each other causing confusion and uncertainty in management. With emergency ultrasound, most of the differential diagnoses for acute calf pain and swelling can be identified with confidence. We present two cases of calf pain and swelling utilising ultrasound to clarify the diagnosis. (Hong Kong j.emerg. med. 2005;12:36-41) Keywords: Popliteal cyst, skeletal muscles, ultrasonography, venous thrombosis, wounds and injuries Case 1 A 56-year-old man presented to the general outpatient clinic in July 2004 complaining of sudden onset of left leg pain and swelling for one week. He denied history of injury. Physical examination revealed a swollen left calf with a circumference 4 cm larger than the unaffected side. Discoloration of bruising was found above the ankle (Figure 1). There was pain on weight bearing and he walked with a limping gait. He was referred to the Accident and Emergency Department (AED) with a provisional diagnosis of deep vein thrombosis (DVT). D-dimer was increased Correspondence to: Chung Kin Lai, FRCSEd, FHKAM(Emergency Medicine) Tuen Mun Hospital, Accident & Emergency Department, Tsing Chung Koon Road, Tuen Mun, N.T., Hong Kong klchung@ctimail.com Cheung Kam Yuen, MBBS(HK), PGDipSEM(Bath) Kam Chak Wah, MRCP, FRCSEd, FHKAM(Emergency Medicine) Figure 1. Discoloration of bruising above the left ankle.

2 Chung et al./ultrasound diagnosis of acute calf swelling 37 to >1000 mg/l (Normal <500 mg/l). Colour Duplex sonography by the emergency physician did not show any evidence of DVT. In view of the gravitational bruise detected, soft tissue injury was suspected. Musculoskeletal ultrasound examination of the left calf was performed with a high frequency (7-12 MHz) linear array transducer. A complete tear of the medial head of the gastrocnemius was confirmed (Figures 2a & 2b). The Achilles tendon was found to be intact. After further enquiry, the patient recalled a history of trying to push-off from his toes before the onset of calf pain. After weeks of cylinder cast immobilisation, physiotherapy was started. Two months after the injury, the patient could walk independently without pain. Follow-up scanning showed decreased anechoic haematoma with reparative process starting from the periphery (Figure 3). Case 2 A 61-year-old man presented to the AED in July 2004 complaining of sudden onset of right leg pain and swelling for one week. He denied any history of trauma. Physical examination revealed a swollen and tender right calf. DVT was suspected and he was admitted to the observation ward. A radiologist performed colour Duplex sonography the next day and no evidence of DVT was found. A small area of bruising above the ankle was detected after a repeat examination. Musculoskeletal ultrasound performed by an emergency physician revealed a small tear of the distal part of the medial head of gastrocnemius (Figures 4a & 4b). A small Baker's cyst was also found incidentally (Figure 5). Compression by transducer with real time scanning did not show any leakage of fluid. In view of the small size of the gastrocnemius tear, he was treated with rest, ice, compression, elevation and early weight bearing as tolerated. Four weeks after the injury, the patient recovered well and was asymptomatic. (a) (b) Figure 2. Complete tear of the medial head of gastrocnemius. (a) Longitudinal sonogram of the left calf showing a well defined anechoic collection (*) between the medial head of gastrocnemius (G) and the soleus (S). (Split screen technique was used for a more complete view of the myotendinous tear.) (b) Transverse sonogram of the same patient showing the elliptical anechoic collection (*). Figure 3. Transverse sonogram of the left calf two months after the injury showing decreased size of the haematoma (*) and the reparative process as hypoechoic areas starting from the periphery of the haematoma (arrows).

3 38 Hong Kong j. emerg. med. Vol. 12(1) Jan 2005 Discussion (b) Figure 4. Partial tear of the medial head of gastrocnemius. a) Longitudinal sonogram of the right calf showing a small tear (*) at the most distal and medial portion of the medial head of gastrocnemius. b) Transverse sonogram of the same patient showing the small tear (*). Figure 5. Transverse sonogram of the medial side of the popliteal region showing a Baker's cyst consisting of 3 portions: a base (B), a neck (N), and a superficial part (S), with the neck lying between the semimembranosus tendon (SM) and the medial head of gastrocnemius. (a) Acute calf pain and swelling are common causes of emergency department attendance. The differential diagnoses include DVT, Baker's cyst, muscular injury, tumour, infection, arterial aneurysm, and Archilles tendon pathology. 1 Careful history taking and physical examination can usually reveal the diagnosis. Much emphasis has been placed on the diagnosis of DVT owing to its serious risk of pulmonary embolism. However, as illustrated by our cases, diseases may mimic each other causing confusion in diagnosis and uncertainty in management. On the other hand, dual pathology of DVT and Baker's cyst has been reported in 3% of DVT and the compressive effects of the cyst may predispose to the development of DVT. 2 Additional investigations are needed to clarify the situation. D-dimer assay has a high negative predictive value for DVT and has been shown to be useful in ruling out this condition. 3 Unfortunately, it may also be raised in inflammatory arthritis or muscle injury with associated haemorrhage. 4 Emergency ultrasound is inexpensive, safe, quick and widely available. The improvement of ultrasound equipment in recent years is astonishing and has extended its applications. With the additional ability of colour Doppler, power Doppler, tissue harmonic imaging, and high frequency linear transducer, most of the differential diagnoses for acute calf pain and swelling can be identified with confidence. DVT remains a major concern for emergency physicians. Delayed diagnosis and treatment may lead to serious consequences. On the other hand, over-aggressive treatment with empirical anticoagulants can be disastrous to patients with ruptured Baker's cyst or muscle injury. In emergency rooms without 24 hours sonologist support, emergency physicians should master the skill in venous sonography to expedite the decision. Gray scale B mode ultrasound can demonstrate venous incompressibility in DVT. The addition of colour duplex sonography reveals the lack

4 Chung et al./ultrasound diagnosis of acute calf swelling 39 of venous flow and helps to identify deep veins even down to the calf level. 5 Ultrasound for DVT is not without limitations. It is operator dependent and can be technically difficult. The sensitivity is low for calf DVT and imaging for pelvic DVT is virtually impossible. Therefore, ultrasound should be used with caution in the pregnant patient with lower extremity swelling because there is a higher prevalence of pelvic DVT in these patients. 6 Complete ultrasound evaluation of the deep venous system from the groin to the lower calf can be time consuming and may not be feasible in a busy emergency department. An alternative approach of 'limited ultrasound' has been studied. This is a twoview technique that only images the B-mode compression of the common femoral vein in the groin and the popliteal vein in the popliteal fossa. Lensing et al found this practice to be effective while Poppiti et al demonstrated a dramatic time reduction from 37 to 5.5 minutes for limited ultrasound compared to complete duplex ultrasound studies. 7,8 Studies combining the use of a pretest probability score, D-dimer assay, and limited ultrasound showed promising value in the management of DVT. 9,10 Blaivas et al suggested incorporation of duplex imaging for visualisation of flow and augmentation. 11 They believed that colour Doppler helped to visualise vessels that otherwise would have been difficult to locate. Baker's cysts were first described in 1840 by Adams as 'popliteal cysts'. 12 It was from Baker's writing in 1877 that we derive the commonly used term 'Baker's cyst'. 12 They represent distension of the gastrocnemiussemimembranosus bursas, which usually communicate with the knee joints in adults. Baker's cysts are common. Fielding et al 13 reported a 5% incidence in patients undergoing magnetic resonance imaging of the knee for the investigation of internal derangement. Small cysts found incidentally may not be the cause of symptoms. 14 Sansone et al noted that Baker's cysts were associated with one or more internal knee disorders in 94%. 15 Intra-articular disorders and excessive joint effusion play an important role in the pathogenesis of Baker's cysts. Baker's cysts become symptomatic when complicated by rupture, dissection, infection or haemorrhage. Robertson et al 16 reported a case of sciatic nerve compression due to proximal dissection. In many centres, ultrasound has largely replaced conventional arthrography as the initial assessment of Baker's cysts. 17 Ultrasound demonstates Baker's cysts to be composed of three portions: a base, a superficial part, and a neck in between. 18 The neck of the bursa lies between the gastrocnemius and the semimembranosus tendons. Baker's cysts can be complicated by dissections, which are usually distal. 17 The most common presentation is extension of the Baker's cyst dorsal to the gastrocnemius muscle to a subcutaneous location. A less frequent presentation is dissection of the fascial planes between the soleus and the gastrocnemius muscles. 18 Large Baker's cysts like those resulting from rheumatoid arthritis can rupture, resulting in changes within the surrounding fat and muscle. These changes are due to inflammation secondary to enzymes found in the bursal fluid. The clinical appearance of the leg is indistinguishable from that of acute thrombophlebitis and is often referred to as 'pseudothrombophlebitis'. 18 Ruptured Baker's cysts are characterised by a pointed instead of the usually rounded inferior border on ultrasound. Gentle compression with the transducer may show fluid extravasating into the surrounding tissues. This again demonstrates the superiority of dynamic ultrasound scanning compared with other static imaging modalities. Tear of the medial head of the gastrocnemius muscle, also known as tennis leg, is the most common muscle tear in the calf. This injury is commonly seen in the intermittently active middle-aged athlete who is often referred to as the weekend warrior. 19 It is a musculotendinous disruption of varying degrees that results from an acute forceful push-off with the foot. The patient complains of sudden calf pain with or without

5 40 Hong Kong j. emerg. med. Vol. 12(1) Jan 2005 an audible 'pop'. The mechanism of injury can be trivial and easily missed if not specifically asked for. The examination may reveal asymptomatic calf swelling and discoloration of bruising. Ultrasound is useful to confirm the tear, to assess the severity and to follow up the progress. An extensive or complete tear appears as an anechoic space between the disrupted medial head of gastrocnemius and the aponeurosis of the soleus. Occasionally, it looks similar to an ectatic vein on longitudinal scan. Doppler flow analysis or scanning in another plane would clarify the diagnosis. 17 Small tears can be missed if not being scanned carefully. Most of these small tears affect the distal and most antero-medial portion of the medial head. 20 Detailed scanning reveals muscle fibers and fibro-adipose septa not reaching the aponeurosis. Initial treatment is mainly conservative. Choice and duration of treatment can be tailor-made according to the severity of the tear. Large tears can be treated by short-term cast immobilisation while small tears can be treated with rest, ice, compression, elevation, and early weight bearing as tolerated. The current opinions towards early ultrasound guided aspiration of the intramuscular haematoma are controversial. Kane et al 1 claimed marked symptomatic and functional improvement immediately after aspiration. Contradictorily, Bianchi et al 20 found this procedure frustrating with frequent early recurrence of fluid collection. Follow up ultrasound examination shows the reparative process as a hypoechoic area starting from the periphery of the haematoma and gradually advancing towards the centre while the amount of central fluid decreases in size. 18,20 Other significant causes of calf pain or swelling like Achilles tendon rupture or inflammation, popliteal aneurysm, cellulitis or abscess all have characteristic sonographic features and can be readily differentiated by bedside ultrasound. The role of emergency ultrasound in modern emergency medicine is undisputed. Emergency physicians frequently face the challenge of calf pain and swelling. We believe that ultrasound can clarify the diagnosis in most situations and should be the initial investigation of choice. References 1. Kane D, Balint PV, Gibney R, Bresnihan B, Sturrock RD. Differential diagnosis of calf pain with musculoskeletal ultrasound imaging. Ann Rheum Dis 2004;63(1): Langsfeld M, Matteson B, Johnson W, Wascher D, Goodnough J, Weinstein E. Baker's cysts mimicking the symptoms of deep vein thrombosis: diagnosis with venous duplex scanning. J Vasc Surg 1997;25(4): Bockenstedt P. D-dimer in venous thromboembolism. N Engl J Med 2003;349(13): McEntegart A, Capell HA, Creran D, Rumley A, Woodward M, Lowe GD. Cardiovascular risk factors, including thrombotic variables, in a population with rheumatoid arthritis. Rheumatology (Oxford) 2001;40 (6): Wolf KJ, Fobbe F. Color Duplex sonography. New York: Thieme; Tracy JA, Edlow JA. Ultrasound diagnosis of deep venous thrombosis. Emerg Med Clin North Am 2004; 22(3): Lensing AW, Prandoni P, Brandjes D, et al. Detection of deep-vein thrombosis by real-time B-mode ultrasonography. N Engl J Med 1989;320(6): Poppiti R, Papanicolaou G, Perese S, Weaver FA. Limited B-mode venous imaging versus complete colorflow duplex venous scanning for detection of proximal deep venous thrombosis. J Vasc Surg 1995;22(5): Schutgens RE, Ackermark P, Haas FJ, et al. Combination of a normal D-dimer concentration and a non-high pretest clinical probability score is a safe strategy to exclude deep venous thrombosis. Circulation 2003;107(4): Tick LW, Ton E, van Voorthuizen T, et al. Practical diagnostic management of patients with clinically suspected deep vein thrombosis by clinical probability test, compression ultrasonography, and D-dimer test. Am J Med 2002;113(8): Blaivas M, Lambert MJ, Harwood RA, Wood JP, Konicki J. Lower-extremity Doppler for deep venous thrombosis--can emergency physicians be accurate and fast? Acad Emerg Med 2000;7(2): Curl WW. Popliteal cysts: historical background and current knowledge. J Am Acad Orthop Surg 1996;4 (3): Fielding JR, Franklin PD, Kustan J. Popliteal cysts: a reassessment using magnetic resonance imaging. Skeletal Radiol 1991;20(6): Munk PL, Vellet AD, Levin MF. Leaking Baker's cyst detected by magnetic resonance imaging. Can Assoc Radiol J 1993;44(2): Sansone V, de Ponti A, Paluello GM, del Maschio A.

6 Chung et al./ultrasound diagnosis of acute calf swelling 41 Popliteal cysts and associated disorders of the knee. Critical review with MR imaging. Int Orthop 1995; 19(5): Robertson CM, Robertson RF, Strazerri JC. Proximal dissection of a popliteal cyst with sciatic nerve compression. Orthopedics 2003;26(12): Torreggiani WC, Al-Ismail K, Munk PL, et al. The imaging spectrum of Baker's (popliteal) cysts. Clin Radiol 2002;57(8): Van Holsbeeck MT, Introcaso JH. Musculoskeletal ultrasound. 2nd ed. St Louis: Mosby; Saglimbeni AJ. Injuries of the medial calf. Available from URL: topic157.htm. Accessed 9th Sep Bianchi S, Martinoli C, Abdelwahab IF, Derchi LE, Damiani S. Sonographic evaluation of tears of the gastrocnemius medial head ("tennis leg"). J Ultrasound Med 1998;17(3):