|Year : 2013 | Volume
| Issue : 3 | Page : 143-145
3D CT appearance of exophytic mastoid fibro-osseous lesion
Krishnan Nagarajan1, Sethupakkam Balasundaram Jothiramalingam2
1 Department of Radiology, Chettinad Hospital and Research Institute, Kanchipuram, Tamil Nadu, India
2 Department of Otorhinolaryngology, Chettinad Hospital and Research Institute, Kanchipuram, Tamil Nadu, India
|Date of Web Publication||2-Sep-2013|
Department of Radiology, Sri Manakula Vinayagar Medical College, Pondicherry - 605 107
Source of Support: None, Conflict of Interest: None
Exophytic osseous lesions are rare in the bones of skull and face. The exophytic lesions like, osteochondroma or extra-osseous (soft tissue) osteoma may not be differentiated by imaging alone. We report a case of pedunculated osseous lesion arising from the retro-auricular mastoid bone that turned out, histopathologically, to be fibro-osseous lesion.
Keywords: 3D CT, Computed tomography, Exophytic, Fibro-osseous lesion, Mastoid
|How to cite this article:|
Nagarajan K, Jothiramalingam SB. 3D CT appearance of exophytic mastoid fibro-osseous lesion. Indian J Otol 2013;19:143-5
| Introduction|| |
Benign tumors of lamellar bone, the osteomas, are relatively common in the skull and paranasal sinuses. They are usually sessile lesions, but occasionally they can be extra-osseous or even pedunculated. Pedunculated lesions may mimic the exostosis (or osteochondromas) or rarely the parosteal osteosarcomas. Although, osteomas have been described from all parts of the temporal bone-the mastoid, external auditory canal, internal auditory meatus and even the middle ear, fibro-osseous lesions are recently reported from the same locations.  One such variant with unique location and characteristic features is the protuberant fibro-osseous lesion of the temporal bone.  We describe a 15-year-old boy presenting with retro-auricular bony swelling that was proved, histopathologically, to be a fibro-osseous lesion.
| Case Report|| |
A 15-year-old boy presented with a slowly progressive bony enlargement behind the pinna of left ear over a period of four years. On examination, the swelling was bony hard with smooth surface and with normal skin over the lesion. High resolution Computed Tomography (CT) of temporal bones was done with 6-slice CT (Brilliance, Philips using collimation 6 × 1.5 mm, table feed 1.5, reconstruction thickness 2 mm) and images were reformatted and volume-rendered (VR) in the workstation. CT showed a well-defined lesion showing punctuated areas of calcific densities with lucencies in between [Figure 1] and [Figure 2]. No indentation or erosion of underlying mastoid was noted. The lesion was centered over the occipito-mastoid suture and had a clear-cut plane of cleavage with the underlying outer table of mastoid bone. The middle ear cavity with ossicles, external auditory canal, inner ear structures and internal auditory meati were normal, bilaterally. The lesion was removed in toto during surgery and submitted for histopathological examination. The histopathological diagnosis is that of fibro-osseous lesion.
|Figure 1: (a and b) Axial CT sections (bone window) show well-defined retro-auriuclar lesion with calcific densities overlying the occipito-mastoid suture|
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|Figure 2: (a and b) Volume rendered images (viewed from left lateral and basal aspects) showing ossified lesion 'stuck' on the mastoid|
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| Discussion|| |
Protuberant fibro-osseous lesion of the temporal bone is a recently described entity with specific characteristic features. It was first described by Selesnick et al.,  in 1999 and subsequently by Sia et al., in 2009  who included two more cases with similar findings, and termed them as 'Bullough's lesions'. The lesion was intimately related to the occipito-mastoid suture and typically presenting as a retro-auricular soft tissue mass with calcific densities, confined to the soft tissues on the outer table of the skull without intra-osseous involvement. The lesion is characterized histologically by rounded and ovoid zones of ossification within a bland fibrous stroma.
Maesa Plaza et al.,  described a calcified lesion using CT and called it as an ossifying fibroma. However, the characteristic location overlying the occipito-mastoid suture, calcific densities within the retro-auricular mass and the clear plane of cleavage with underlying mastoid makes this lesion most likely belonging to the group of 'protuberant fibro-osseous lesion'.
Due to a plane of cleavage with underlying bone, the differential diagnosis can be parosteal osteosarcoma and soft tissue (extra-osseous) osteomas. Li et al., in their case report, on a soft tissue osteoma involving the pterygo-mandibular space, have described the following three criteria to define extra-osseous osteoma that; there should not be any preceding trauma or inflammation, the lesion should not be of developmental origin and finally, there should not be any attachment to underlying periosteum of bone or peri-articular structures. 
Our case fits in the features of protuberant fibro-osseous lesion and the 3D CT showed calcified matrix and the plane of cleavage very well. Though the diagnosis was made histopathologically, the characteristic location and other features of this entity makes pre-operative diagnosis possible using CT and 3D reformations.
| References|| |
|1.||Ramírez-Camacho R, Vicente J, García Berrocal JR, Ramón y Cajal S. Fibro-osseous lesions of the external auditory canal. Laryngoscope 1999;109:488-91. |
|2.||Sia SF, Davidson AS, Soper JR, Gerarchi P, Bonar SF. Protuberant fibro-osseous lesion of the temporal bone: "Bullough lesion". Am J Surg Pathol 2010;34:1217-23. |
|3.||Selesnick SH, Desloge RB, Bullough PG. Protuberant fibro-osseous lesions of the temporal bone: A unique clinicopathologic diagnosis. Am J Otol 1999;20:394-6. |
|4.||Maeso-Plaza AM, Gómez-Ullate Alvear J, Ortega del Alamo P. Ossifying fibroma of the mastoid area. Acta Otorrinolaringol Esp 2009;60:146-7. |
|5.||Li G, Wu YT, Chen Y, Li TJ, Gao Y, Zhang J, et al. Soft-tissue osteoma in the pterygomandibular space: Report of a rare case. Dentomaxillofac Radiol 2009:38:59-62. |
[Figure 1], [Figure 2]