Journal of Clinical Imaging 25 (2001) 388 – 391
Frontal sinus mucocele A rare complication of craniofacial fibrous dysplasia ¨ stu¨ner, ˙Ilhan Erden, Serdar Akyar C ¸ etin Atasoy*, Evren U Ankara University Medical Faculty, Department of Radiology, I˙bn-i Sina Hospital, Samanpazarı 06100, Ankara, Turkey Received 31 May 2001
Abstract We present plain radiographic, computed tomographic and magnetic resonance imaging (MRI) findings in a 25-year-old female patient with craniofacial fibrous dysplasia (FD). Although FD has a tendency to involve craniofacial bones in a unilateral fashion, the involvement was bilateral and extensive in this case. An additional feature was the presence of a frontal sinus mucocele, presumably due to the involvement of the sinus recess by the dysplastic process. This complication of the craniofacial FD has been reported very infrequently in the literature. D 2001 Elsevier Science Inc. All rights reserved. Keywords: Fibrous dysplasia; Cranium; Mucocele; Paranasal sinus; Computed tomography; Magnetic resonance imaging
1. Introduction Fibrous dysplasia (FD) is a benign developmental skeletal disorder characterized by bony expansion secondary to replacement of the medullary cavity by fibroosseous connective tissue. Most of the patients have monostotic involvement affecting the ribs and extremities. However, craniofacial involvement is also not rare, especially in the polyostotic form of the disease. Craniofacial lesions are usually unilateral [1]. Herein, we report a rare manifestation of polyostotic craniofacial FD characterized by extensive disease affecting both sides of the cranium. A further discriminating feature of the case was the association of a frontal sinus mucocele, presumably due to blockage of the sinus ostium by the disease process. This complication has been reported very infrequently in the literature [2– 6].
2. Case report A 25-year-old female patient presented with a 2-year history of swelling in the left frontal region, left-sided * Corresponding author. Kırım Caddesi, S¸enyuva Sitesi, N2/21, Emek 06510, C ¸ ankaya, Ankara, Turkey. Tel.: +90-312-2158259; fax: +90-3123107117. E-mail address:
[email protected] (C ¸ . Atasoy).
anosmia and blurred vision in her left eye. Physical examination revealed protrusion in the frontal region, proptosis and decreased visual acuity in the left eye. Frontal and lateral skull radiographs showed thickening and sclerosis of the frontal, sphenoid and left ethmoid bones and lateral wall of the left orbit. There was a large wellmarginated lytic lesion in the region of the frontal sinus. Computed tomography (CT) demonstrated massive expansion in the frontal, sphenoid, nasal bones, left ethmoid sinuses and the clivus. The anterior parts of the left parietal and temporal bones were also affected. The thickening predominantly involved the diploe and had a ground-glass appearance (Fig. 1a). The lesion in the region of the frontal sinus had well-defined lobulated margins and a homogeneous density in the range of water (Fig. 1b). Both optic canals were narrowed and the left ocular bulb was displaced anteroinferiorly. The thickened craniofacial bones demonstrated low-signal intensity on both T1- and T2-weighted spin – echo sequences, and enhanced markedly after intravenous injection of Gd-DTPA. The cystic lesion in the left frontal sinus was slightly cerebrospinal fluid (CSF)-hyperintense on T1-weighted and CSF-isointense on T2-weighted images, and showed mural enhancement after the injection of Gd-DTPA (Fig. 2). The patient was referred to surgery with a diagnosis of craniofacial FD and frontal sinus mucocele, where a cranioplasty was performed and the mucocele excised.
0899-7071/01/$ – see front matter D 2001 Elsevier Science Inc. All rights reserved. PII: S 0 8 9 9 - 7 0 7 1 ( 0 1 ) 0 0 3 2 0 - 5
C¸. Atasoy et al. / Journal of Clinical Imaging 25 (2001) 388–391
389
Fig. 1. Axial CT of the head. (a) Section at the level of the optic canals shows the ground-glass texture of the thickened bones. Although predominantly left-sided at this level, the dysplastic process also extended to the right causing the narrowing of both optic canals. Note the inferior part of the mucocele (asterisk). (b) At a higher level with narrower window settings, the content of mucocele is isodense to CSF. Bilateral and extensive involvement of the anterior cranium is appreciated.
Fig. 2. Axial MR images. (a) T1-weighted image shows the heterogeneous low-signal intensity of the affected bones. The CSF hyperintense mucocele has an intermediate-intensity lining (arrows). (b) The mucocele appears isointense with CSF on the T2-weighted image, where the thickened bones also show a heterogeneous low-signal intensity. (c). Note the marked enhancement of the affected bones, as well as the lining of the mucocele (arrows) on postgadolinium T1-weighted image.
390
C¸. Atasoy et al. / Journal of Clinical Imaging 25 (2001) 388–391
3. Discussion FD is a disorder of unknown etiology in which the bone marrow is replaced and subsequently expanded by fibroosseous tissue. The disease generally affects older children, adolescents and young adults [7]. The commoner monostotic form of FD, characterized by single-bone involvement primarily in the extremities and ribs, tends to become quiescent with cessation of growth. The polyostotic form affects multiple bones usually in a unilateral distribution and may continue to progress beyond puberty. When polyostotic FD is associated with precocious puberty and skin pigmentations, it is termed the McCune – Albright syndrome [6]. Craniofacial involvement, which occurs more frequently in the polyostotic disease, tends to have a typical hemicranial or hemifacial distribution that helps to distinguish FD from Paget’s disease, which is often bilateral [1,8]. In some patients, however, large areas of bone dysplasia may cross suture lines and affect both sides of the cranium [6], as was the case in this patient in whom the anterior cranium was, in a Pagetoid fashion, extensively and bilaterally involved with resultant narrowing of both optic foramina. Since FD primarily affects the bone marrow, the craniofacial form of the disease is characterized by expansion of the diploic space with secondary displacement of the outer table and sparing of the inner table, features used to differentiate FD from Paget’s disease. Sparing of the inner table of the skull also distinguishes FD from the hyperostosis associated with meningiomas [7]. The diploic space widened by fibrocellular connective tissue has a characteristic ground-glass appearance, which is better appreciated by CT than on radiographs. Small sclerotic and lytic areas may be distributed throughout the ground-glass background of diploe. Bone thickening may lead to cosmetic problems including frontal prominence and proptosis, diplopia, restricted ocular mobility and several cranial nerve deficits particularly visual and hearing problems secondary to narrowing of neural foramina [6]. Encroachment on the neural foramina is better evaluated with cross-sectional imaging methods such as CT, and preferably magnetic resonance imaging (MRI). The affected bones usually have a low- to intermediate-signal intensity on both T1- and T2-weighted sequences [1], probably owing to the replacement of the marrow cavity by fibrous tissue. However, the lesions may have quite variable signal intensity on T2-weighted images, where they may appear hyperintense depending on the activity of the lesions. On postgadolinium MR images, affected bones show variable enhancement, reflecting vascularity of the fibrocellular tissue. Marked enhancement, as occurred in this patient, was shown to occur in lesions that show clinical and histological activity [1]. Association of a mucocele with craniofacial FD is a very rare occurrence that has been reported in only a handful number of cases [2 – 6]. This complication most probably
results from the involvement and subsequent occlusion of the recesses of the sinuses by the dysplastic process [2]. In our patient, thickened left ethmoid septae caused obliteration of the left frontal sinus recess. Mucoceles have variable CT density and MR signal intensity. On CT, they may appear either hypo- or hyperdense [9]. Protein concentration and viscosity of mucoceles determine their T1-weighted signal intensity, which may range from hypointensity to hyperintensity. The various signal intensities encountered on T2-weighted images reflect their state of hydration [10]. In most cases, mucoceles can be reliably differentiated from paranasal sinus carcinomas on noncontrast MR images. While malignant processes, especially squamous cell carcinomas, often display intermediate-signal intensity on both T1- and T2-weighted images, mucoceles frequently have high T2-weighted signal intensities. Occasionally, however, neoplastic diseases, in particular, minor salivary gland and nerve sheath tumors, may appear hyperintense on T2-weighted images mimicking mucoceles. In such cases, accurate differentiation may require contrast-enhanced MR images, where most tumors show solid enhancement, unlike mucoceles, which exhibit only mural enhancement, if at all [10]. In summary, polyostotic craniofacial FD may rarely involve both sides of the cranium. Besides the well-known obliteration of the paranasal sinuses, an unusual sinusrelated complication of the disorder is the development of a mucocele, probably secondary to occlusion of the sinus recesses by the thickened bones. Despite the various and potentially confusing CT and MRI features, the typical location in the region of a paranasal sinus, well marginated contours and internal homogeneity, coupled with a nonenhancing or a ring-enhancing lesion, may allow a confident differential diagnosis of mucoceles from other more aggressive complications of this disorder including sarcomas and aneurysmal bone cysts.
References [1] Casselman JW, De Jonge I, Neyt L, De Clercq C, D’Hont G. MRI in craniofacial fibrous dysplasia. Neuroradiology 1993;35:234 – 7. [2] Birch S, Cook PL. Mucocele of the sphenoid sinus complicating fibrous dysplasia. Br J Radiol 1979;52:998 – 1001. [3] Som PM, Lidov M. The benign fibroosseous lesion: its association with paranasal sinus mucoceles and its MR appearance. J Comput Assisted Tomogr 1992;16(6):871 – 6. [4] Dowler JG, Sanders MD, Brown PM. Bilateral sudden visual loss due to sphenoid mucocele in Albright’s syndrome. Br J Ophthalmol 1995; 79(5):503 – 4. [5] Hirabayashi S, Kagawa K, Ohkubo E, Sugawara Y, Sakurai A. Craniofacial fibrous dysplasia with rapidly increasing proptosis due to a mucocele behind the globe. Ann Plast Surg 1998;40(2): 182 – 5. [6] Furin MM, Eisele DW, Carson BS. McCune – Albright syndrome (polyostotic fibrous dysplasia) with intracranial frontoethmoid mucocele. Otolaryngol — Head Neck Surg 1997;116(4):559 – 62.
C¸. Atasoy et al. / Journal of Clinical Imaging 25 (2001) 388–391 [7] Schonder A. Fibrous dysplasia of bone with proptosis. Am J Dis Child 1977;131:678 – 9. [8] Swartz JD, Vanderslice RB, Korsvik H, Saluk PH, Popky GL, Marlowe FI, Wolfson RJ. High resolution computed tomography: Part 6. Craniofacial Paget’s disease and fibrous dysplasia. Head Neck Surg 1985;40 – 7 (Sep/Oct).
391
[9] Tassel PV, Lee Y, Jing B, De Pena CA. Mucoceles of the paranasal sinuses: MR imaging with CT correlation. AJNR 1989;10: 607 – 12. [10] Lanzieri CF, Shah M, Krauss D, Lavertu P. Use of gadoliniumenhanced MR imaging for differentiating mucoceles from neoplasms in the paranasal sinuses. Radiology 1991;178:425 – 8.
