A rare cause of insidious shoulder pain in a young female: A soft tissue aneurysmal bone cyst in supraspinatus muscle.

Aneurysmal bone cyst (ABC) is an expansile cystic lesion which may affect any bone of the skeleton. Although extremely rare, lesions with histomorphological characteristics of an ABC occur in the soft tissue. Herein, we report the first case of ABC involving the supraspinatus muscle and mimicking common pathologies, such as myofascial pain syndrome or subacromial impingement syndrome.

Introduction

Aneurysmal bone cyst (ABC) is an expansile cystic lesion of numerous blood-filled channels which may affect any bone of the skeleton. It was first described by Jaffe and Lichtenstein[1] in 1942. In 1972, Salm and Sissons[2] defined soft tissue lesions resembling ABCs, and it was probably the first description of this pathology. Soft tissue ABC is a rare entity, with about 20 cases reported in the literature until now.[3] Few cases have been reported in the literature presenting with shoulder pain. Herein, we report the first case of ABC presenting with shoulder pain and involving the supraspinatus muscle and discuss its clinical features and imaging findings in a young female.

Case Report

A 21-year-old female patient was admitted to our clinic with an insidious shoulder pain, which was not related to activity for one year. Her medical history revealed no trauma or repeated shoulder movement causing damage to rotator cuff tendons. Physical examination findings were normal, except for mild tenderness in the supraspinatus tendon. Laboratory tests and direct X-ray results were unremarkable. Magnetic resonance imaging (MRI) of the shoulder was planned, as the symptoms persisted after one week of conservative treatment. The MRI revealed multiple cystic lesions with the fluid liquid level of approximately 4 to 5 cm in diameter in the supraspinatus muscle, posterior to the coracoid process, primarily considered as an ABC. Contrast enhancement in the periosteum and mass in soft tissue were observed, suggesting an inflammatory reaction (Figures 1 and 2). The patient was referred to orthopedics and traumatology outpatient clinic. Shoulder computed tomography (CT) was taken for detailed evaluation of the bone involvement and destruction of the spine scapula by an expansive tumor mass was detected (Figure 3). Complete resection was planned and a written informed consent was obtained from the patient.

Complete resection of the mass was performed. Histomorphology of the excised material showed fibroblastic proliferation, osteoclast type giant cells with osteoblastic rim isolated from soft tissue with more mature bone tissue areas, compatible with an ABC. Four months after surgery, the range of motion of the shoulder was not limited in all directions. However, she was complaining of mild weakness during prolonged activity. The rehabilitation program consisting of strengthening exercises, electrical stimulation of periscapular muscles and transcutaneous electrical nerve stimulation (TENS) was applied for five a week for a total of four weeks. The patient is still under follow-up for possible tumor mass recurrence.

Discussion

Aneurysmal bone cyst is a benign, blood-filled lesion in the bone which tends to expand or grow. It most often affects individuals in their second decade of life as in the presented case with a median age of 13 years, and 90% of lesions are detected before 30 years of age.[4] Females are slightly more affected with an estimated male-to-female sex ratio of 1:1.16.[4] Few cases of soft tissue ABC were reported in the literature in the upper arm, including triceps muscle, retroclavicular and infraspinous region.[5,6] However, supraspinatus muscle involvement has not been described in the literature, yet. To the best of our knowledge, this is the first case of ABC involving the supraspinatus muscle.

Initially an ABC was thought to be a non- neoplastic condition, but recently, reproducible clonal chromosomal abnormalities have been described in both osseous and extraosseous ABCs, suggesting a probable neoplastic nature.[7-9] These cysts are typically solitary and are, currently, thought to arise either as primary neoplasms or secondary lesions adjacent to osteoblastomas, chondroblastomas or giant cell tumors.[10,11]

Although benign, ABCs can be locally aggressive. Their expansile nature can cause pain, swelling, deformity, disruption of growth plates or joint surfaces, neurological symptoms (depending on location), and pathological fractures. In our case, there was a mild shoulder pain, independent from the movement. On her physical examination there was tenderness on the supraspinatus muscle, mimicking myofascial pain syndrome. Robinson et al.[12] compared a series of seven patients in whom a neoplasm was the underlying cause for the stiff shoulder with a series of 50 patients with primary or secondary frozen shoulder. In addition to a detailed history taking, physical examination, radiography, ultrasonography, and bone scanning were performed in all cases. The authors concluded that the most useful diagnostic test appeared to be a discrete area of bony tenderness, which was present in all seven patients with a tumor and in only five of 50 patients in the control group.

The diagnosis of ABCs is made based on various imaging modalities, exhibiting typical features such as fluid-fluid levels, although biopsy is critical, as telangiectatic osteosarcoma cannot be excluded based on imaging studies alone.[13] Neither the cause of rotator cuff syndrome or supraspinatus tendinitis was present in our patient, nor did they present physical examination findings compatible with these diagnoses. Therefore and, considering the age of the patient, we did not prefer the treatment methods we frequently apply in shoulder problems such as trigger point injection, intra-articular injection, subacromial injection, or physical therapy.

Histologically, ABCs (both osseous and soft tissue) are comprised of blood-filled cysts with fibrous septa, which also contain giant cells, reactive woven bone, and fibroblasts. The hemorrhagic cystic spaces with peripheral woven bone are what cause ABCs (both soft tissue and osseous) to have their well-defined, expansile, lytic appearance with peripheral calcification on radiographs and CT.[5,14,15]

Differential diagnosis for soft tissue ABCs includes myositis ossificans, nodular fasciitis with osteoclast- type giant cells, ossifying fibromyxoid tumor of the soft parts, calcified hematoma, extra-skeletal telangiectatic osteosarcoma, and giant cell tumor of soft tissue. A combination of clinical history, imaging characteristics, and pathological examination can allow differentiation of each entity.[3]

The typical peripheral calcification of soft tissue ABCs is not seen in nodular fasciitis and, thus, the entities should be readily differentiated by radiological-pathological correlation. On CT, nodular fasciitis lesions appear to be non-specific soft tissue masses, and MRI appearances are variable depending on the cellularity of the lesion.[16]

An ossifying fibromyxoid tumor may also feature peripheral woven/lamellar bone such as soft tissue ABCs, but in a more lobular and aggressive pattern on radiographs/CT, as opposed to the characteristically smoother margins of soft tissue ABCs. Ossifying fibromyxoid tumors featuring blood filled cystic spaces and fluid-fluid levels on MRI have not been reported, so far.[17]

Radiologically, giant cell tumors of soft tissue do not tend to have a calcified rim, such as soft tissue ABCs. Giant cell tumors of the soft tissue can rarely feature cystic change, necrosis, and/or hemorrhage with formation of fluid-fluid levels, although not usually to the extent of a soft tissue ABC. On histopathology, soft tissue ABCs usually contain more reactive osteoid and woven bones, but fewer giant cells than a giant cell tumor of soft tissue or giant cell tumor of the tendon sheath.[18]

Clinical history often yields an antecedent history of trauma for myositis ossificans. The typical fluid-fluid levels and septated “honeycomb” enhancement pattern of soft tissue ABCs should not be seen.[19]

On radiography and CT, extra-skeletal telangiectatic osteosarcoma will typically feature a wider zone of transition and more aggressive and invasive behavior as a result of its malignancy. On MRI, an extra-skeletal telangiectatic osteosarcoma usually features fluid-fluid levels, but tends to have more nodularity and soft tissue components, as opposed to the septated “honeycomb” appearance of soft tissue ABCs.[20]

Treatment of ABCs is highly challenging, due to their locally aggressive nature and high rates of recurrence. Complete resection has the lowest rates of recurrence, but at the cost of high morbidity to the patient.[21] Despite best efforts at curettage, clinical series have shown highly variable recurrence rates, with some series showing rates as high as 59%.[22] As a result, various adjuvants have evolved to reduce recurrence including the use of cement, high-speed burr, argon beam, phenol, and cryotherapy.[22] Although radiation is most notably utilized in the treatment of malignancies, radiotherapy has historically been used to treat ABCs primarily, as an adjuvant therapy in cases of recurrence and in inoperable ABC lesions.[23] Currently, the treatment strategy of choice relies largely on the approach and experience of the treating physician: minimize risk at the cost of increased recurrence and potentially repetitive treatment or accept risks with a more invasive, definitive procedure to reduce recurrence.[21] Complete resection of the mass was performed in our case and, after operation, a rehabilitation program consisting of strengthening exercises, electrical stimulation of periscapular muscles, and TENS was applied for five days per week over four weeks. She is still under follow-up for possible tumor mass recurrence.

In conclusion, soft tissue ABCs can occur in any age group and typically appear as peripherally calcified soft tissue masses with lucent/hypodense centers on radiographs/CT, and hemorrhagic spaces with fluid-fluid levels and enhancing “honeycomb” septations on MRI and it should be kept in mind as a rare cause of shoulder pain.