British Journal of Radiology 75 (2002),916-918 © 2002 The British Institute of Radiology
Aneurysmal bone cyst of the ethmoid bone
K A Hrishikesh, DNB
1
R S Narlawar, DMRD
2
S B Deasi, MD
1
K Aniruddha, MD
1 and
S Maheshwari, MD
1
1 Department of Radiology, Jaslok Hospital and Research Centre, Mumbai and 2 Department of Radiology, K.E.M. Hospital, Parel, Mumbai 400 012, India
Correspondence: Dr Ranjeet S Narlawar
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Abstract
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Aneurysmal bone cysts (ABCs) are benign, slow growing expansile lesions usually found in long bones or vertebrae. Plain radiography reveals expansion of bone and cortical thinning. MRI may assist in diagnosis by virtue of its ability to demonstrate blood–fluid levels, which is a characteristic finding in these lesions. Very few cases of ABC of the paranasal sinuses have been reported in the literature. We present MRI findings of ABC of the ethmoid sinus in a 19-year-old male.
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Case report
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A 19-year-old male presented with a slow growing swelling over both sides of the nose with bilateral proptosis, left greater than right, of 3 years duration. There was a history of epistaxis controlled by nasal packing around 5 years prior to presentation. The patient also gave a history of anosmia. Physical examination of the lesion showed a non-tender swelling approximately 8 cm x 6 cm in size. Lateral skull radiography (Figure 1
) revealed boney expansion in the frontal region with involvement of the ethmoid sinuses. CT of the paranasal sinuses confirmed an expansile boney mass centred over the ethmoid sinuses. Axial (Figure 2) and sagittal (Figure 3) MRI revealed the presence of a large cystic expansile mass causing the expansion of the ethmoid sinuses. The septated mass caused displacement of the orbits laterally and anteriorly, and revealed the presence of multiple fluid levels within. The mass also showed enhancement following contrast administration (Figure 4). A pre-operative angiogram was also performed to assess the intracranial extent and blood supply of the mass. Bifrontal craniotomy with 80–90% excision of the tumour was performed. The tumour extended into the anterior cranial fossa, frontal and ethmoid sinuses and into both nostrils. Macroscopically the tumour was cystic, whitish-grey in appearance and haemorrhagic on incision. The inner surface was smooth with multiple fibrous septae dividing the cyst in multiple small cavities. Microscopic examination revealed several blood filled channels bordered by a thin layer of spindle-shaped endothelial cells, surrounded by connective tissue containing numerous multinucleated giant cells. The patient had an uneventful post-surgical course.
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Figure 1. Lateral radiograph of the skull showing expansile osteolytic lesion in the frontal region with soft tissue and intracranial extension.
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Figure 3. T1 weighted sagittal MR image shows heterogeneous hyperintense cystic mass in the anterior cranial fossa.
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Figure 4. T1 weighted, post-contrast, fat suppressed axial MR image showing heterogeneous enhancement of the solid components of the lesion.
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Discussion
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Aneurysmal bone cysts (ABCs) typically involve the long bones of the extremities, membranous bones of the thorax and pelvis, or vertebrae. The midline of the skull base is not the site of predilection for ABC and involvement of ethmoid sinus is extremely rare. There have been occasional reports of involvement of sphenoid and maxillary sinus [1, 2]. Skull involvement accounts for 3–6% cases [3, 4]. ABC is a benign lesion of obscure pathogenesis, usually found in patients younger than 20-years-old [5]. The affected bone balloons and expands with many communicating cavities containing venous blood [6]. Microscopic examination reveals blood-filled channels bordered by a thin layer of spindle-shaped endothelial cells, surrounded by connective tissue containing numerous multinucleated giant cells [4]. Haemosiderin laden macrophages and new bone formation is found within the stromal matrix [7]. ABC most likely represents a degenerative process associated with other primary bone lesioins [8]. ABC in the paranasal sinuses is rare, with only four previous cases having been described in the sphenoid and ethmoid sinuses [9]. The presence of multiple giant cells may cause difficulty in differentiating the lesion histologically from osteoclastoma, fibrous dysplasia, ossifying haematoma and cavernous haemangioma of bone. The principal diagnostic error occurs if the histologist fails to appreciate the lining of the blood-filled spaces. Radiological differential diagnosis of such a lesion includes giant cell reparative granulomas, giant cell tumour, haemorrhagic cysts and fibrous dyplasia. Giant cell tumours are usually seen in an older age group (>30 years of age) [10]. Giant reparative granulomas usually have a definite precedent history of trauma. Fluid–fliud levels may appear whenever fluids of differing densities are contained in a cystic or compartmentalized structure. They have been described in both ABC and giant cell tumours. Fibrous dysplasia does not usually reveal fluid–fluid levels and commonly involves the frontal and ethmoid bones [11]. On CT, ABCs are typically lytic, expansile and surrounded by a thin shell of bone. Within the cyst, fluid and blood levels are present. MRI shows similar features. The presence of paramagnetic blood breakdown products give rise to fluid levels of varying signal intensities ranging from very bright signal (extracellular methaemoglobin) on T2 weighted imaging to a very low signal (intracellular deoxyhaemoglobin, cellular debris or haemosiderin) [12]. In conclusion, a variety of entities may be considered, but the MRI features described may be helpful in the differential diagnosis of expansile boney lesions in the skull base.
Received for publication September 5, 2001.
Revision received May 15, 2002.
Accepted for publication June 13, 2002.
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References
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