Diagnostic and therapeutic value of ultrasonography in the detection of paralabral ganglion cysts with a curved array transducer: A case report

1. Introduction

Paralabral cysts are rarely found in the shoulders, and have a prevalence of 2–3% in the general population [1]. Paralabral ganglion cysts are often located paralabrally around the spinoglenoid notch, suprascapular notch, or infraspinatus fossa, and are associated with superior labrum anterior to posterior (SLAP) lesions and instability of posterior joints [2]. Cysts sometimes cause suprascapular nerve entrapment, which often causes pain during shoulder movement [3, 4].

Magnetic resonance imaging (MRI) is the gold standard to confirm paralabral ganglion cysts. However, computed tomography (CT) or ultrasound (US) scans can also be used for its diagnosis [1, 2, 5, 6]. In shoulder US, linear transducers are often used because most lesions are not deep and are located around the rotator cuff tendon [2]. However, US using linear transducers is limited when the target structure is located deep or underneath a bone, as in the case of paralabral ganglion cysts [7, 8]. The US of patients with shoulder pain may fail to identify nodular cysts because these cysts are often deep and located far from the rotator cuff tendon. Moreover, the acromion of the scapular often hinders US imaging using linear probes [6]. Particularly, nodular cysts may be missed in patients who do not present with muscular atrophy, decreased muscle strength, or abnormal electrodiagnostic findings, as in our patients.

Selecting the appropriate US transducers is important in various clinical situations and images. Rectangular images are obtained from a linear array, and angular images in the shape of a pie slice with a bite taken out of its top are obtained in a convex array. Even when a linear array is used, a phase array can be used to obtain trapezoidal images. However, a convex array with smaller frequencies is more appropriate in visualizing deeper structures [9]. Therefore, to evaluate deep structures below anatomical barriers, such as paralabral ganglion cysts below the acromion, convex transducers are more appropriate than linear transducers.

In paralabral ganglion cysts, CT- or US-guided aspiration and steroid injection can reduce pain [5, 10, 11, 12], and a suprascapular nerve block can be performed if suprascapular nerve entrapment is present [3, 4]. Furthermore, intra-articular injections are sometimes used to treat SLAP lesions, which are related to causes of paralabral ganglion cysts [14, 15]. If these conservative treatments are not effective, surgical treatment through arthroscopy can be considered [11, 12, 3, 4, 13, 14, 15, 16].

Herein, we report convex transducer US and MRI findings of two patients who presented with shoulder pain and had paralabral cysts located on the posterior-superior labrum acetabulare to the spinoglenoid notch which could not be confirmed using a linear transducer. We compared pain and functional evaluation before and after various US-guided procedures.

The institutional review board of the Jeonbuk University Hospital approved this case report and waived the requirement for informed consent (IRB number 2020-05-028).

2. Case report

Two patients (case 1, a 44-year-old man; case 2, a 41-year-old man) complained of severe pain during shoulder movement. The pain was present mostly during shoulder extension, abduction, or external rotation, and was particularly severe when lifting heavy objects or lifting the hands above the head. The visual analog scale (VAS) scores were 4 at rest and 7 upon shoulder movement in case 1, and 3 at rest and 8 upon minimal shoulder movement in case 2. On physical examination, no abnormality was found on upper extremity manual muscle test or in the range of motion of the joint in both patients, and there was no tenderness in the surrounding muscles. The Hawkins-Kennedy test was negative in case 1 but positive in case 2. Both patients had no notable medical, family, or psychosocial history.

On plain radiography of the shoulder, no abnormalities were found in the alignment of the glenohumeral joint, acromioclavicular joint, and distal clavicle, as well as in bone density, cartilage space, and soft tissues [17].

US (Affiniti70G, Philips, Bothell, WA, USA) with an 18-4 MHz linear transducer was performed. In case 1, other than subacromial-subdeltoid bursitis, no abnormality was found in the tendons surrounding the shoulder. A subacromial-subdeltoid bursa injection using corticosteroid was then performed under US guidance via a linear array transducer. In case 2, partial thickness tears of the subscapularis and supraspinatus were noted. Therefore, corticosteroids were injected into the subscapularis and supraspinatus (SS) tendons under US guidance with a linear array transducer. Polydeoxyribonucleotide was also injected into the SS under US guidance, after follow-up. The patients still complained of subjective symptoms even after these treatments.

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Shoulder MRIs were done for both patients because the shoulder pain persisted even after US-guided procedures using a linear transducer for rotator cuff lesions. In case 1, a nodular lesion of 2 × 1 × 11.2 cm that extended from the posterior-superior labrum acetabulare to the spinoglenoid notch was noted, with no injury to the labrum or entrapment of the suprascapular nerve (Fig. 1A). In case 2, a 21.32 × 8.69 mm nodular lesion was found anterior to the superior labrum acetabulare and anterior to the supraspinatus muscle, SLAP lesions and supraspinatus tendon partial-thickness tears were also noted (Fig. 1D).

Electrodiagnostic tests using Synergy ® Machine (Medelec Ltd., Surrey, UK) were conducted to check for abnormalities in the suprascapular nerve. A nerve conduction study was performed, by applying stimulations at the Erb’s point and recording the stimuli at the supraspinatus and infraspinatus muscles and showed similar latency and amplitude bilaterally in both cases.

Although the same site was evaluated using linear transducer US for interventions following the shoulder MRI, the lesions could not be visualized (Fig. 1B and E). The imaging study was limited because the acromion of the scapular blocked the site of the lesion. Therefore, a 6-2 MHz convex transducer, which enables visualization of deeper structures at wider angles, was used. In case 1, a 2.1 × 0.65 cm homogeneous cystic echo was noted around the spinoglenoid notch (Fig. 1C), and in case 2, a 2.22 × 0.98 cm homogeneous cystic echo was found inferior to the acromion (Fig. 1F). The lesions were similar in sizes to the paralabral ganglion cysts confirmed on MRI.

The ultrasonographic images using a linear array transducer were difficult to identify the cyst even after the confirmation at the shoulder MR arthrogram. We changed to a curved array transducer and the images using a curved array transducer gave us the exact location of the lesion. After the visual verification of the cystic lesion in ultrasonographic images using a curved array transducer, we performed US-guided cyst aspiration and intra-cystic injection with the curved transducer. In both cases, the lesions were either gelatinous or mucoid; hence, very little fluid was obtained on aspiration. Subsequently, a mixture of 1% lidocaine 3 cc and 5 mg/ml dexamethasone was injected into the cystic lesions [11, 12, 16]. Due to persistent symptoms, US-guided intra-articular injection into the shoulder, and then suprascapular nerve block using a linear transducer was performed for treatment and diagnostic intervention.

Visual analog scale (VAS) and shoulder pain and disability index (SPADI) were recorded to track pain changes before and after each intervention. However, the evaluation between study participants was not performed in the same period after injection due to the outpatient schedule. The SPADI that consists of a total of 13 questions; 5 questions regarding the severity of an individual’s pain and 8 questions described to assess the degree of functional disability, were recorded before and after interventions [18]. Pain on VAS decreased from 7 to 6 after intra-articular injection in case 1, and from 8 to 7 after cyst aspiration and intra-cystic injection in case 2. According to the previous study of the minimal clinically important difference in postoperative pain using VAS, a change of VAS score of 1.23 ∼ 1.88 was minimal to moderate change, and 2.01 was a large change [19]. After each intervention, minimal to moderate change of pain score were noted in both cases. SPADI decreased from 61.5 to 50 after intra-articular injection in case 1. In case 2, SPADI decreased gradually after each intervention. (Table 1). No other changes in VAS and SPADI were noted after other interventions. In both cases, no adverse effects were recorded during each intervention. However, the patients were referred to the orthopedic surgeon for arthroscopy and nodular cyst removal and were scheduled for follow-up because of persistent discomfort.

Although a few case reports of the ganglionic cysts at the labrum have been published to date, no further ultrasound studies used a curved transducer. In the present cases, the ultrasound study using a curve transducer plays a beneficial role in the diagnosis and intervention of the ganglionic cysts below the acromion. We confirmed the presence of paralabral ganglion cysts, in patients with persistent shoulder pain using MRI, when it could not be visualized on linear transducer US. Since linear US transducers that are often used for musculoskeletal examinations cannot visualize deep structures or those underneath bones, the site of lesions was detected in the ultrasound study using a convex transducer. Moreover, we performed cyst aspiration and intra-cystic injection with a convex transducer on the ganglion cysts [11, 12, 16]; VAS and SPADI were mildly improved, compared to before and after each intervention.

In the diagnosis of paralabral cysts, MRI is the gold standard, and MR arthrogram leads to more accurate diagnoses because it can also confirm damages to the labrum [1]. However, their time and economic constraints are challenges in performing MRI for all patients with shoulder pain. Therefore, US is used for relatively simpler diagnosis and treatment generally in patients with shoulder pain [8].

No particular treatment is required for asymptomatic paralabral nodular cysts. However, when the cyst is large or depending on the location, it may cause suprascapular nerve entrapment, requiring intra-articular evaluation and surgical treatment using arthroscopy. Moreover, pain requires active physiotherapy and pharmacological therapy. When pain persists despite 4–6 months of conservative treatment, CT- or US-guided aspiration of the lesion may be helpful [21]. Fritz et al. reported that CT-guided aspiration of nodular cysts of the shoulder improved the symptoms [22], and Fehrman et al. reported a treatment algorithm depending on the symptom in suprascapular nerve entrapment caused by nodular cysts [21]. However, CT-guided treatment of nodular cysts is limited, as the cyst cannot be clearly distinguished from the surrounding soft tissues, leading to diminished accuracy of the procedure [23].

Several reports have been made on aspiration and injection treatment for nodular cysts. When US-guided cyst aspiration was performed for 15 patients with paralabral ganglion cyst, symptoms improved in 86% of these patients even when the aspirated fluid was only around 1 ml [10]. Moreover, in 4 patients with paralabral cyst and suprascapular nerve entrapment, US-guided aspiration led to symptomatic improvement [5]. Out of 20 paralabral ganglion cyst patients who received steroid injections, 8 showed complete relief, 10 had moderate symptomatic relief, and 2 had persistent symptoms [12]. Furthermore, another case report revealed that US-guided aspiration and anesthetic/depomedrol injection led to symptomatic improvement [11]. SLAP lesions often accompany paralabral ganglion cysts. In a study that performed intra-articular corticosteroid injection and strengthening exercises of the rotator cuff and periscapular muscles, all 46 patients who received intra-articular injection showed initial symptomatic improvements, but symptoms recurred in 12 patients. Of these 12 patients, five showed improvements after second intra-articular injections and exercise therapy. In seven patients with persistent pain, arthroscopic SLAP repair was performed [13, 14, 15]. Moreover, some studies have reported that suprascapular nerve block with lidocaine with or without cortisone improved shoulder discomfort, and these methods may serve as useful diagnostic approaches [3, 4]. Since paralabral cysts are accompanied by labral damages [1], surgical treatment of the location site of the cyst and the site of labrum reconstruction has been reported to lead to high patient satisfaction [6]. Another study reported that arthroscopy-based surgical treatment was more effective in spinoglenoid notch cysts accompanied by suprascapular neuropathy [23]. In our cases, conservative treatment was first performed. Although VAS and functional evaluation through SPADI showed slight improvements after each intervention, the effects were not significant. As evidenced by the pathophysiology of paralabral cysts and previous report, subsequent labral damages and intra-articular evaluations should be assessed through arthroscopic surgical treatment and diagnosis.

In conclusion, paralabral cysts in the SS inferior to the acromion were visualized relatively easily using a convex transducer. Conservative interventions were then provided, and their effects were monitored. Linear US transducers are often used for musculoskeletal evaluation and intervention for superficial structures. To visualize deeper structures blocked by anatomical barriers, such as bones, convex transducers are expected to improve the diagnostic value and accuracy of interventions. Therefore, in patients with pain upon shoulder movement, especially in those whose pain continues despite appropriate treatment for rotator cuff lesions, US diagnosis of paralabral ganglion cysts using convex transducers will improve the diagnostic value and accuracy of interventions.