|Year : 2010 | Volume
| Issue : 4 | Page : 570-572
Aneurysmal bone cyst of the calcaneum: An expansile locally destructive lesion
Ajay Malik1, Prabal Deb1, NS Mani1, John D'Souza2
1 Department of Pathology, Armed Forces Medical College, Pune - 411040, India
2 Departemnt of Radiodiagnosis, Armed Forces Medical College, Pune - 411040, India
|Date of Web Publication||24-Feb-2011|
Department of Pathology, Armed Forces Medical College, Pune - 411 040
Source of Support: None, Conflict of Interest: None
Aneurysmal bone cyst (ABC) is a benign but locally destructive lesion affection of which in the calcaneum has rarely been reported in the literature. We report an unusual case of ABC of the calcaneum in a 17-year-old-male, who presented with painful ankle swelling with difficulty in walking. Radiology revealed benign cystic calcaneal lesion, without any evidence of fracture. Biopsy was characterized by formation of osteoid along with the presence of ecstatic blood-filled channels, consistent with ABC. However, this being an uncommon site for ABC, histopathology needs to be used to differentiate it from other benign and malignant entities, and a definitive diagnosis warrants clinical and radiological correlation. Most of the ABCs require surgical curetting and bone engraftment of the surgical defect.
Keywords: Aneurysmal bone cyst, calcaneum, multiloculated cyst
|How to cite this article:|
Malik A, Deb P, Mani N S, D'Souza J. Aneurysmal bone cyst of the calcaneum: An expansile locally destructive lesion. J Can Res Ther 2010;6:570-2
| > Introduction|| |
Tumors of the calcaneum are rare entities.  Aneurysmal bone cysts (ABCs) are multiloculated cystic growths of the bone, which are known to enlarge rapidly and cause local destruction. ABC is mainly seen in the metaphysical regions of the long bones and the vertebrae.  ABCs of the calcaneum are uncommon, and generally present as chronic heel pain and swelling, but may rarely present as pathologic fracture.  We report an unusual case of ABC of the calcaneum in a 17-year-old-male, who presented with painful ankle swelling with difficulty in walking, without any radiological evidence of fracture.
| > Case Report|| |
A 17-year-old male presented with a painful swelling on either side of the right ankle since 7 months. This was associated with difficulty in walking since 5 months. He did give a vague history of blunt trauma while playing football, prior to the onset of symptoms. Radiographic examination of his ankle revealed a multiloculated cystic lesion of the calcaneum with thin cortical trabeculae traversing the cystic cavity. There was no breaking out of the cortical bone or any soft tissue involvement. Based on these radiographic features, an opinion of a benign cystic calcaneal lesion was offered [[Figure 1]a, b].
|Figure 1: (a-f) Lateral and anteroposterior view of the right ankle showing radiolucent multiseptate lesion of the calcaneus without any soft tissue component. Photomicrograph showing multiple blood-filled ecstatic cystic spaces with focal endothelial lining along with few multinucleated giant cells in a spindle cell stroma surrounding the vascular spaces (C: H and E, ×40) (D: H and E, ×100) (E: H and E, ×200), which focally contained benign osteoid (F: H and E, ×400).|
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Aspiration of the cystic contents revealed occasional cyst macrophages along with peripheral blood elements. There were no atypical cells. Subsequently, he underwent curettage of the cystic lesion followed by bone chips grafting.
Gross examination of the curetted specimen received for histopathological examination showed fragments of reddish-brown granular bits of tissue. Microscopic examination of the decalcified tissue bits displayed presence of ectatic cavernous spaces of varying caliber interspersed by thin traversing fibrous septae. Focally, the vascular spaces lacked any endothelial lining or smooth muscle cells, unlike that of normal blood vessels. The fibrous septae and intervening solid areas showed the presence of spindle cells without any mitosis or atypia. The solid appearing areas revealed reactive osteoid formation, which was partially surrounded by osteoblasts and spindle cell stroma. Presence of an occasional multinucleated giant cell scattered within the fibrous stroma was also noted. There was no evidence of chondroid or chondromyxoid stroma [[Figure 1]c-f]. Based on the histopathological profile, an opinion of ABC of the calcaneum was offered.
The patient was administered a course of broad-spectrum antibiotics. The postoperative period was uneventful. The patient was followed up for the next 3 months during which there was no evidence of recurrence. Subsequently, he was lost to follow-up.
| > Discussion|| |
Bone cysts of the calcaneum are rare lesions. This may include a wide spectrum of non-neoplastic cysts, benign or malignant neoplastic lesion ranging from simple bone cyst, ABC (primary or secondary), chondroblastoma, giant cell tumor (GCT), and an osteosarcoma with secondary ABC formation, to an ossifying hematoma or pseudotumor of hemophilia.
ABC of the calcaneum is a rare entity. ABCs have predilection for the knee joint of the young,  have an equal incidence in both genders, and are encountered half as frequently as GCTs.
Clinically, calcaneal cysts are often symptomatic, although some of these lesions may remain asymptomatic and are detected as incidental findings. Radiologically, these lesions are expanding lytic lesions, which may show fluid levels on computed tomography (CT) scan, which is a resultant of blood layering.  A unicameral bone cyst is a common, benign, fluid-filled lesion found almost exclusively in children. This radiolucent lesion may be encountered virtually in any bone, but typically, it is affects the proximal parts of either the humerus or the proximal femur, in contrast to the classical ABC.  On radioimaging studies, an ABC may be misdiagnosed as a more commonly occurring multilocular unicameral cyst.
The histologic diagnosis of an ABC of the calcaneum is essentially one of exclusion. In the presence of osteoid formation, it is imperative that extensive sampling of the tissue be carried out, especially of the solid appearing foci, to exclude any other neoplastic lesion.
Areas similar to an ABC can be seen in a GCT, chondroblastoma, chondromyxoid fibroma and fibrous dysplasia. Feature that distinguishes an ABC from a neoplasm is that it can regress even after incomplete removal. However, currently, with the detection of the presence of USP6 fusion gene, mainly CDH11-USP6, a neoplastic origin of these lesions is being contemplated upon. 
Clinically, an ABC may mimic a GCT of the calcaneus, though the latter are less polycystic.  Further, on histology, ABC is characterized by the presence of large amount of serosanguineous fluid and the ectatic vascular channels, which are partially lined by giant cells and lacking a well-defined endothelial lining, unlike a GCT.
ABC arising secondary to chondroblastoma typically affects the epiphysis. Telangiectatic osteosarcoma may be one of the more ominous differential diagnoses which need consideration, especially in a setting of unequivocal radiology. However, histologically, ABC is characterized by well-defined regular margins with eggshell rims and without any soft tissue component, unlike an osteosarcoma which is exemplified by anaplastic cells along with atypical mitotic figures. ,
Despite a favorable outcome of ABCs with an overall cure rate of 90-95%,  one of the most common problems encountered during management is frequent recurrence. The incidence of recurrence has been noted to vary between 59% in cases treated with intralesional excision  and 0% in cases with resection.  Ideally, a patient of ABC needs to be observed for a longer period of time to exclude any recurrence. However, in the present case, since the patient was lost to follow-up after an initial observation of 3 months, this was not possible.
To conclude, ABC of the calcaneum is an extremely uncommon entity. Proper diagnosis entails correlating the clinical presentation, anatomical location, radiological profile, and histopathological appearance. This is imperative not only to exclude other more common histological mimics, but also for choosing the appropriate therapeutic regimen and prognosticating the disease outcome.
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