A large aneurysmal bone cyst of the rib

Clinical History

A 22-year-old female patient with complaint of right side chest pain and discomfort in association with right shoulder and back pain for more than 2 years. In radiology department chest radiography and ultrasound were performed followed by chest CT and MRI examinations.

Imaging Findings

Chest radiography showed a large opacity in the middle and lower zones of the right hemithorax (Fig. 1) while the chest ultrasound showed a lobulated cystic lesion with echogenic internal septations (Fig. 2).
For further investigation an unenhanced and contrast-enhanced CT was performed, which demonstrated a large expansile multiloculated cystic lesion in the right hemithorax originating from the posterior arch of 8th rib. The mass lesion measured 9.9x7x8.8 cm. Some of the loculation within the lesion demonstrates fluid-fluid level and the septations inside the cyst were clearly enhanced after IV contrast injection (Fig. 3).
MRI T2 weighted images confirmed a multiloculated cystic structure with fluid-fluid level as well (Fig. 4).

Discussion

For the first time, aneurysmal bone cyst of the rib (ABC) was reported by Jaffe and Lichtenstein in 1942 [1]. ABC can affect all the ribs except the last 3 and as a whole the involvement of ribs comprises 2.7% of all ABC cases [2]. The main aetiology of the disease is unknown, however, the disturbance in arterio-venous circulation could mostly be the reason [3]. Another mentioned aetiology of ABC is the increased pressure of venous circulation or trauma, which causes bone absorption and formation of blood- filled cysts [4]. ABCs usually occur primarily but some cases demonstrate secondary to lesions like fibrous dysplasia, angiochondroblastoma, haemangioendothelioma, cartilogenous haematoma or giant cell tumours [2]. The tumour is an expansile destructive bone lesion containing various sizes of cystic structures filled by blood or serum. The cysts are separated by septas which are composed of loose spindle cells or benign giant cell septas [4]. A palpable lump with limited movement, pathological fracture and pain are the main features of ABC, but in 29% of cases the tumour is totally asymptomatic and is found incidentally in a routine chest X-ray [5]. CT and MRI images demonstrate multiple cavernous spaces which are filled by fluid-fluid levels [3]. The radiographic differential diagnosis comprises giant cell tumour, plasmocytoma, chondrosarcoma, fibrous dysplasia, chondormyxoid and metastasis [5]. Ewing sarcoma and eosinophilic granuloma are included in the differential diagnosis as well [4]. Core needle biopsy specimens can be performed for confirmation of the diagnosis. Biopsy needs to be done carefully due to risk of bleeding from blood cavities inside the ABC [2]. The histopathological examination reveals a non-malignant bone lesion that is composed of blood-filled cysts and trabeculae. The cysts are lined with cuboidal cells consisting of osteoid tissue, fibroblasts and giant cells [1, 2]. Different treatment strategies have been proposed for ABC; surgical removal, radiotherapy, cryotherapy, sclerotheraphy and embolization. The best option with the lowest risk of recurrence is total excision [6]. In surgery following the removal of the tumour the affected part of the rib is cut as well. The recurrence rate is between 11-31%. Non-operable cases can be treated by radiotherapy [7]. Selective arterial embolization is another choice of treatment, especially for those ABCs which are difficult for surgery due to site or size [6].

Differential Diagnosis List

Final Diagnosis

Aneurysmal bone cyst of the rib

URL:	https://www.eurorad.org/case/13005
DOI:	10.1594/EURORAD/CASE.13005
ISSN:	1563-4086