Abstract

Fibrous dysplasia is a category of fibro-osseous lesions which demonstrates replacement of normal bone by a fibrous connective tissue matrix, within which varying amounts of metaplastic osteoid, immature and mature bone & in some instances, cementum like tissue are deposited. Among the two types of fibrous dysplasia, like the monostotic forms and the polyostotic form; the monostotic type of fibrous dysplasia is more commonly seen. We present a case of an isolated monostotic fibrous dysplasia of the temporal bone with clinical, radiographic, microscopic features along with the management of the same.

1. Introduction

Fibrous dysplasia (FD) is a developmental disorder of bone which may be due to reactive or unknown etiologies and they all behave in a benign fashion with a defective osteoblastic differentiation and maturation ¹. It was first described by McCune and Bruch and the term “Fibrous Dysplasia” was coined by Lichtenstein ². The three variants of FD seen are unifocal/monostotic type of FD, where a single bone is involved, a multifocal/polyostotic type where multiple bones are involved and McCune Albright Syndrome (MAS) when the polyostotic type bone lesions are associated with cutaneous pigmentation i.e. Cafe-au-lait spots (Jaffe-Lichenstein syndrome) and disorders of endocrine system like pituitary adenomas, precocious puberty or hyperthyroidism ³. Fibrous dysplasia involving the craniofacial bones is of particular importance in oral and maxillofacial surgery as they cause severe deformities and dysfunctions. These lesions are more commonly predominant in males compared to females (2: 1) and preference for Caucasians ⁴. Even though the craniofacial skeleton is a frequent site of the disease, temporal bone affection is rare ⁵. We report a case of an isolated monostotic fibrous dysplasia of the temporal bone with a review the literature.

2. Case Report

A 38 years old woman presented herself to our department with a chief complaint of swelling and pain of the right temporal region. The swelling had started as a small growth and increased gradually over a period of 4 years. On clinical examination, a diffuse, lobulated bony hard mass was palpable extending from the preauricular region till the middle of the zygomatic arch on the right side (Figure 1 and Figure 2). Pain was localized, chronic and intermittent in nature. There were no associated symptoms like ear pain, hearing loss and facial nerve weakness or paralysis.

A computed tomography scan of the face was taken and the lateral 3D computed tomography scan revealed a radiopaque, multilobed bony mass extending from the temporal region to the zygomatic arch sparing the glenoid fossa (Figure 3).

No ear canal stenosis was noted. No other bones were found to be involved except the bone at the temporal region.

Blood and other laboratory investigations were found to be normal. A biopsy was done under local anesthesia. The histological slide showed fibrous tissue stroma with irregularly shaped bone trabeculae confirming the diagnosis of monostotic fibrous dysplasia (Figure 4).

After an informed consent was obtained from the patient, shewas operated for surgical resection and recontouring of the lesion through a preauricular approach under general anesthesia (Figure 5). The lesion was segmentally resected (Figure 6) conservatively and bone was contoured according to the anatomical shapes and defining the bony facial contour. After achieving a good hemostasis, the flap was closed in layers (Figure 7) and a postoperative follow-up of the patient was done for a week (Figure 8). A periodic follow up of the patient was done at regular intervals for any recurrence of the lesion.

3. Discussion

Fibrous dysplasia involving the temporal bones has been well documented in the literature ^{5, 6, 7, 8, 9, 10, 11}. The involvement of temporal bone is more common with craniofacial polyostotic FD (PFD) or MAS ¹², and less common in monostotic disease ^{13, 14}. Monostotic type contributes to approximately 80-85% of fibrous dysplasia with a less degree of bone deformity as compared to that of the polyostotic type. This form occurs most frequently in the age range of 10-70 years of age with the mean age being 27 years. The male to female ratio of about 2: 1 is usually seen with a tendency to develop at early childhood ^{1, 4}. The ratio of left and right sides affected is approximately equal to each other and seen commonly in the ribs, femur, tibia and craniofacial bones in the descending order of frequency. Monostotic FD are although truly termed for mandibular lesions, the maxillary lesions often involving the adjacent bones (Zygoma, sphenoid, occiput) are not strictly monostotic. Hence it is ideally termed as craniofacial fibrous dysplasia which is more appropriate for these lesions. The incidence of MFD constitutes for about 70%, PFD for about 30% and McCune Albright Syndrome is for about 3% ¹⁵. Following maxilla and mandible, all the craniofacial bones may be involved but involvement of temporal and occipital bones are unusual. It also occurs in an isolated form. In the isolated variety, no extracranial lesions are present. Site of involvement most commonly include the frontal, sphenoid, maxillary and ethmoidal bones with the occipital and temporal bones being least commonly affected. The craniofacial skeleton is one of its predictive sites and therefore the temporal bone may become involved. The involvement of temporal bone between all cranial bones is around 18%. It is also observed that the temporal bone is affected unilaterally, but bilaterally involvement may be seen in PFD cases ^{15, 16}. The characteristic signs are the expansion of bone, thinned cortical layer and displacement of surrounding structures ^{16, 17}. These findings were consistent with our present case. Diagnoses of these lesions are possible with biopsy and our case of temporal FD was also confirmed with a biopsy done under local anesthesia prior to surgical intervention.

Radiological appearances can be distinguished as 3 types: pagetoid or ground glass appearance (56%), sclerotic (23%) and cystic (21%) lesions ^{15, 17, 18}. The radiological features in our case demonstrated an increase in size and bone density associated with areas of sclerosis and radiolucency and the CT scan showed a transition zone between normal and dysplastic bone. A differential diagnosis of a eosinophilic granuloma is made in a solitary lesion may and Hand-Schuller-Christian disease in multiple lesions ^{15, 17}.

In some cases, there are associated symptoms like severe cosmetic deformities, recurrent fractures of the involved bone, hearing loss and facial nerve weakness or paralysis. Hearing loss is seen as a result of narrowing of the external auditory canal due to the surrounding FD and fixation of the ossicles within the epitympanum from adjacent involved bone, ranges from mild to moderate degree. An obstruction of the canal with cerumen and desquamated skin leads to a potential complication like cholesteatoma ^{14, 19}. A comprehensive audiology examination and ear evaluation is recommended once the temporal bone is found to be involved with FD ^{14, 20, 21, 22}. If the lesion causes sudden facial weakness due to expansion, then a surgical decompression is considered. Therefore, surgical intervention is required to relieve the obstruction, chronic infection and other complications ^{23, 24}. In the present case, a surgical correction of excision of the lesion and recontouring was done for cosmetic purpose and also as per the patient’s desire. There was no hearing loss or facial nerve weakness noted. Postoperatively the patient had uneventful healing and showed no signs of recurrence during the follow up period of more than 5 years.

While pain is common among FD patients ²⁵, more data relating pain to the location and activity of disease and the effectiveness of various treatment modalities like the use of NSAIDs with and without narcotic treatment; bisphosphonates ²⁶ such as alendronate, pamidronate, or zoledronic acid for craniofacial FD has been considered for pain reduction and to reduce the rate of growth of the lesion ^{27, 28, 29}. The efficacy of these osteoclast inhibitor therapies such as bisphosphonates or denosumab in slowing the growth of craniofacial FD and reducing intractable craniofacial FD pain is yet to be determined by further studies. Also, newlyemerging therapies like RANK ligand inhibition (i.e. denosumab) in the treatment of FD-related pain or reduction in growth remains to be determined ³⁰.

Surgery remains the mainstay of therapy especially in the absence of curative medicine in FD. FD should be readily classified by a thorough and good clinical history and examination followed by radiologic studies, open biopsy and then a decision is made for a surgical intervention. More often a conservative treatment is beneficial, particularly if important or vital structures (such as cranial nerves or the carotid artery) are placed at risk, rather than a radical and aggressive resection of the lesion due to its benign nature. A periodic and long follow up period warrants and keeps the recurrence under check. Radiation therapy is ineffective and contraindicated because of the possibility of malignant transformation ^{5, 7}.

The recommended treatment for FD includes:

1. Early and aggressive screening for efficient management of endocrinopathies (particularly growth hormone excess).

2. A detailed history, clinical examination and radiographic analysis are very essential especially in lesions where a confirmatory biopsy is not possible.

3. Surgical treatment is delayed till until the skeletal maturity in lesions which are quiescent.

4. However, if there are symptoms or rapid changes in the lesion then a surgical contouring or resection may be carried out prior to skeletal maturity, though a high risk of recurrence is seen.

5. Immediate surgical intervention and evaluation is done for active disease (rapid growth, new onset of pain or paresthesia, visual or hearing changes).

6. The use of bisphosphonates may be considered as an adjuvant for refractory pain at the site of the lesion.

7. Amulti-disciplinary approach is vital for the successful management of patients with FD, particularly PFD and MAS ³¹.

4. Conclusion

In summary, fibrous dysplasia involving the temporal bone can be treated relatively conservatively due to its benign nature, with the primary goal being preservation of existing function and surgery being reserved for patients with functional impairment or a cosmetic deformity. With the current understanding of the biologic and clinical characteristics of FD and recommendations for the clinical management in the craniofacial region along with the advent of modern imaging modalities and histopathologic analysis, diagnosis is made very simple and straightforward. Therefore, treatment is customized for each patient based on their needs, the size and sites of involvement and the associated symptoms that follow it.

Acknowledgements

The authors have received permission from the patients depicted in the manuscript to use their photographs for this purpose.

Funding

None.

Competing Interests

The authors declare that they have no competing interests.

References