INTRODUCTION

Fibrous dysplasia (FD) is character-ized by slow, progressive replacement of alocalized area of bone by an abnormal pro-liferation of isomorphic fibrous tissueintermixed with poorly formed, haphaz-ardly arranged trabeculae of woven bone[1]. In 1937, McCune and Bruch first sug-gested that among all of the abnormalitiesof bone formation, this disorder shouldhave its own place as a distinct clinicalentity. The following year, Lichtensteinintroduced the term “fibrous dysplasia”[2]. The lesion of fibrous dysplasiaappears in three distinctive clinical pat-terns: 1) single bone involvement (mono-stotic form), which is the most common

presentation (70 percent of patients); 2)multiple bone involvement (polyostoticform), a less common form (30 percent);3) McCune-Albright syndrome, a rarevariant of polyostotic form with pigmenta-tion and endocrinologic abnormalities [3].

Cranial bone involvement of FD usu-ally presents as an enlarging mass withsymptoms resulting from the mass effectexerted by the lesion. Abnormalities in theposterior fossa have been implicated in thepathophysiology of hindbrain herniationwhich has been thought to be responsiblefor the occurrence of syringobulbia [4].

Aneurysmal bone cyst (ABC) isviewed as a secondary, uncommon, reac-tive lesion of bone, consisting of an arte-rio-venous malformation. ABC occurs

YALE JOURNAL OF BIOLOGY AND MEDICINE 78 (2005), pp. 139-143.Copyright © 2005. All rights reserved.

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*To whom all correspondence should be addressed: Dr. Pervin K. Iseri, Department ofNeurology, University of Kocaeli, Derince, Izmit, Turkey, E-mail: pervin.iseri@gmail.com.Tel.: 90-262-332-21-60. Fax: 90-262-233-54-61. GSM: 90-532-500-07-66.†Abbreviations: ABC, Aneurysmal bone cyst; CSF, cerebrospinal fluid; FD, fibrous dyspla-sia; MRI, Magnetic resonance imaging.

CASE REPORT

Fibrous Dysplasia of the Cranial Bones: ACase Report and Review of the Literature

Pervin K. Iseri,a* Husnu Efendi,a Ali Demirci,band Sezer Komsuoglua

aDepartment of Neurology, University of Kocaeli, Derince, Izmit, Turkey andb Department of Radiology, University of Kocaeli, Derince, Izmit, Turkey

Fibrous dysplasia (FD) is a relatively uncommon disorder that affects primarily the cranialregion; its occurrence in the cranial base in combination with hindbrain herniation andaneurysmal bone cyst (ABC) constitutes an extremely rare condition. We report a case ofpolyostotic fibrous dysplasia with progressive occipital, temporal, and clival involvement.Clinical findings and differential diagnosis with special emphasis on the imaging featureswere discussed. A small posterior fossa volume has been thought to lead to hind brain her-niation. The resultant obstruction to the CSF pathways at the level of the foramen magnumhas been implicated in the development and subsequent progression of syringobulbia.

most commonly in long bones. One of theprimary diseases that may be associatedwith ABC is FD. Only a few cases of ABCaffecting the cranial bones with fibrousdysplasia have been reported [3, 5, 6].

To the best of our knowledge, in theEnglish literature, case reports with thediagnosis of FD do not include all of thesesymptoms together. In this paper, wereport the case of a patient with FD ofoccipital, temporal, parietal bones, clivusand skull base in combination with ABC,hindbrain herniation, and syringobulbia.

CASEA 35-year-old woman presented with

gait disturbance, swallowing difficulty,slurring of speech, vertigo, and alteredsensation of hands. These problems hadbeen progressive over the last severalmonths and were accompanied by pro-gressive hearing loss and tinnitus in theleft ear. More recently, the patient haddeveloped hoarseness. Her physical exam-

ination revealed a bulging, slightly tendermass over her left occipital area. No café-au-lait spots or other skin stigmata werefound. Neurological examination showedhorizontal nystagmus, diminished gagreflex, wasting and weakness of bothupper limbs, pyramidal signs in the lowerextremities, and dissociated sensory lossC4 to C8 dermatomes. Serum levels foralkaline phosphatase, calcium, and PO4were normal. Detailed endocrinologicaltests, including thyroid and parathyroidfunction tests and serum hormone levels(ACTH, growth hormone) were per-formed, and normal values were obtained.

CT of the head showed fibrous dys-plasia of the clivus, temporal, occipitalbones and skull base with an associatedABC of the occipital bone (Figure 1).Magnetic resonance imaging (MRI) con-firmed the findings of FD, hind-brain her-niation, syringobulbia, and ABC (Figures1 and 2). A radionuclide bone scan skele-tal survey was performed. She had cranialbone involvement without manifestations

140 Iseri et al: Fibrous dyplasia of the cranium

Figure 1. (cranial CT findings) :Computerized axial tomographic scanshowing the expansion of the occipital bonewith “ground glass” appearance of fibrousdysplasia.Figure 2. (cranial MRI findings): Sagittalmagnetic resonance image showing fibrousdysplasia of occipital bone and clivus andhind brain herniation.Figure 3. (cranial MRI findings): Axial T2-weighted magnetic resonance image show-ing fibrous dysplasia of temporal, occipitalbones and skull base with an associatedABC of the occipital bone.

Figure 1 Figure 2

Figure 3

in the remainder of the body. An audio-gram demonstrated an ipsilateral conduc-tive hearing loss of 65 dB. Brainstem audi-tory evoke responses confirmed the retro-cochlear involvement of the auditorynerve on the left side.

The patient was consulted by neuro-surgery and ENT surgeons. Total removalof the lesion was considered impossible toperform, and a surgical posterior decom-pression was decided upon. The patientwas advised of the unpredictability of FDand recommended decompression of theskullbase, but she did not accept the oper-ation due to high surgical risks that wereexplained to her.

Since the patient refused surgery, wehad planned to treat her with alendronatmonosodium trihidrate, which is a biphos-phonate. In addition, serial CT scanningwas planned to follow the disease processand progression. She is still on medicaltherapy and has no progression.

DISCUSSIONFibrous dysplasia of the cranium is a

well-described entity of unknown etiologyin which normal bone is replaced byabnormal fibro-connective tissue prolifer-ation [1, 5-7]. Polyostotic FD involvingthe skull base and ABC of the occipitalbone are rare diseases. In addition, onlyone case with hindbrain herniation andsyringobulbia due to FD of skull base hasbeen reported [4]. Our case deserves a spe-cial attention that both ABC and syringob-ulbia due to FD appeared on the samepatient.

In the polyostotic form with extensiveskeletal dissemination, the incidence ofcraniofacial involvement increases to 100percent [8, 9]. The incidence of the loca-tion of the FD lesions involving the crani-um is controversial. In one study, it wassuggested that the most affected cranialbones are the ethmoid (71 percent), sphe-noid (43 percent), frontal (33 percent),maxillary bones (29 percent), and less fre-

quently involved are the temporal (24 per-cent) and occipital bones (5 percent) [5].In other studies, it was reported that thefrontal bones were most commonlyinvolved followed by the sphenoid, eth-moid, parietal, temporal, and occipitalbones [8, 10]. Our case was a polyostaticfibrous dysplasia involving clivus, occipi-tal, parietal, and temporal bones. Due tointense occipital involvement, the foramenmagnum was narrowed. The dysplasticgrowth of the bone of the posterior fossahas led to progressive hindbrain herniationthrough the foramen magnum and devel-opment of a syringobulbia [4].

In the case of FD of the skull base andcranium, the natural history of the diseasecan be more complicated because of thepossibility of neural structure impinge-ment. Craniofacial lesions usually presentwith symptoms resulting from the masseffect exerted by the lesion. Expansivelesions of the bony jugular foramen mayencroach on lower cranial nerves and maycause cranial neuropathies [11]. In thiscase, complications of cranial base FDwere caused by jugular foramen and fossainvolvement resulting in IX and X nerveparalysis. In addition, impingement ofneurovascular structures due to hindbrainherniation, secondary to decreased posteri-or volume, resulted in abnormal cerebellarfindings, syringobulbia, and retrocochlearinvolvement of the 8th nerve. In the chiarimalformation, decreased volume of theposterior fossa has been thought to beresponsible for the occurrence and pro-gression of hindbrain herniation, whichcauses augmentation of cerebrospinalfluid (CSF) pressure [12]. The theory ofcraniospinal CSF pressure dissociation hasbeen suggested to explain thesyringomyelia [13]. Assuming the aboverelationship is valid in our patient, slowprogression of hindbrain herniation sec-ondary to FD could be the cause ofsyringobulbia.

The majority of published cases of FDreport an early age of onset of symptoms

Iseri et al: Fibrous dyplasia of the cranium 141

[14]. In our patient, symptoms of hind-brain herniation did not manifest until thethird decade of life. This may be explainedby the very slow progression of diseasethat began early in development.

The radiographic characteristics ofFD, as described by Fries in 1957, arepagetoid (56 percent), a mixture of denseand radiolucent areas of fibrosis; sclerotic(23 percent), massif homogenously dense;and cystic (21 percent), a spherical orovoid lucency surrounded by a denseboundary [1]. CT is the study of choice fordiagnosis and follow-up because of itssuperior bony detail and accurate assess-ment of extent of the lesion. Furthermore,CT can often assist with differentiatingfibrous dysplasia from other osteodystro-phies of the skull base, including otoscle-rosis, osteogenesis imperfecta, Paget dis-ease, and osteopetrosis [5]. In our case, aCT of the brain was performed andrevealed findings consistent with FD ofthe clivus, left temporal, and occipitalbones. In addition to hindbrain herniationand syringobulbia, aneurysmal bone cystformation with a bony shell and soft tis-sue-appearing center was also readilyapparent on MRI. Although the develop-ment of ABC is a well-known occurrencethroughout the skeletal system, they havenot been frequently described within theskull base [5]. The occurrence of a con-comitant FD and ABC in the occipitalbone is exceedingly rare. Only three casesof FD andABC affecting the cranial boneshave been reported [3, 5, 6].

The onset of craniofacial involvementis usually insidious, characterized by abarely noticeable, gradually increasing,painless swelling in the neurocranium.Although FD is a benign and slowly pro-gressive disorder, in the late stage of thedisease expansion of the cranial bones cancause mass effect on the cranial structures.As in our case, the progressive growth ofthese lesions may cause difficulties inmanagement. When the disease producessymptoms, conservative treatment is the

preferred management. Subtotal resectionwith close follow-up is required, particu-larly if important and vital structures areplaced at risk [5]. Radiation therapy isineffective and contraindicated because ofpossibility of malignant transformation[8]. Some pharmacological agents recom-mended avoiding the progress of the dis-ease. Although bisphosphonates have beenused for treating patients with osteodystro-phies, their effects have been limited inpatients with FD. Bisphosphonates effectsby inhibiting osteoclastic bone resorptionand limits expansion of the bone. In theabsence of curative medicine for fibrousdysplasia, surgery becomes the major ther-apy. In this patient, we had to use the med-ical therapy since she did not pursue pos-terior decompression surgery.

FD of cranial bones is a progressivedisease that can cause severe complicationif removing of the dysplastic tissue cannotbe done in the early stage of the disease, asin our patient. In some studies, it is report-ed that surgical treatment is needed whenthe patients have significant clinical symp-toms [2, 5]. Since lesions in the late stageof FD in the skull base can cause life-threatening problems, we think that thesurgery can be done before significantclinical symptoms occur.

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