Fibrous Dysplasia of the Maxilla: Diagnostic

Original Article

Fibrous Dysplasia of the Maxilla: Diagnostic Reliability of the Study Image. Literature Review Massimo Fusconi1 Michela Conte1 Martina Pagliarella2 Anna Teresa Benincasa1 Simone Alessi1 Andrea Gallo4 1 Department of Sensory Organs, University “La Sapienza” of Roma,

Rome, Italy 2 Department of Applied Clinical Sciences and Biotechnologies, Università dell’Aquila, Aquila, Italy 3 Radiodiagnostic Department, Sant’Andrea Hospital, Rome, Italy 4 Department of Surgical Sciences, University of Rome “La Sapienza,” Rome, Italy

Chiara De Vincentiis3

Armando De Virgilio1

Address for correspondence Anna Teresa Benincasa, Via Bertarelli, Rome, Italy (e-mail: [email protected]).

Abstract

Keywords

► ► ► ► ►

fibrous dysplasia radiology Paget ossifying fibroma osteosarcoma

Objective Fibrous dysplasia (FD) is a benign bone disorder in facial bones. This study evaluates the possibility of diagnosing fibrous dysplasia on imaging alone, without biopsy of the lesion, which is often burdensome for the patient. Materials and Methods The authors bring their experience of four cases of bone lesions of the maxillofacial region and present a review of published studies. The imaging techniques evaluated are computed tomography (CT) and magnetic resonance imaging (MRI) with and without contrast. Results The literature review demonstrates that it is impossible to make diagnosis of fibrous dysplasia exclusively by imaging. Radiographic images often show a groundglass appearance, which is characteristic but not pathognomonic of fibrous dysplasia. Conclusion Although CT and MRI images may in many cases suggest a diagnosis of fibrous dysplasia, histological examination or follow-up imaging should follow.

Introduction Fibrous dysplasia (FD) is a pathologic condition in which normal bone is altered by abnormal fibro-osseous tissue, causing distortion and overgrowth of the affected bone. The areas of fibrous tissue are interwoven with newly formed bone trabeculae that vary in size and shape. FD has been classified into three categories: monostotic FD, where only one bone is involved (70%); polyostotic FD, where multiple bones are involved (30%); and McCune-Albright syndrome, where FD is associated with café au lait spots and multiple endocrinopathies (rare).1–3 FD is caused by a gene mutation of a cell surface receptor guanine nucleotide protein (G protein).2 Mutation in the gene for Gsa (GNAS1) is associated with the range of

received December 2, 2012 accepted March 5, 2013

fibrous dysplasia disorders. This mutation occurs in a somatic cell producing somatic mosaicism. FD mainly affects the younger population, 75% under the age of 30 years.4 Following the ribs, craniofacial bones are the second most common site of involvement and account for 25% of cases.5 The craniofacial lesions caused by Paget disease (PD), ossifying fibroma (OF), and osteosarcoma (OS) may be clinically and radiologically confused with those of FD, so a certain diagnosis can be made only by histological examination.6,7 In this study we deal with the differential diagnosis of FD because of the difficulties encountered in clinical practice. Our experience included four patients with fibro-osseous lesions of the facial bone. Given the greater complexity of

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Fibrous Dysplasia of the Maxilla

Fusconi et al.

obtaining a biopsy sample, we initially tried to make the diagnosis only with diagnostic imaging, but we got unsatisfactory results. The authors present a review of published studies concerning the comparison of radiological features observed on computed tomography (CT) and magnetic resonance imaging (MRI) scans of the various fibro-osseous lesions of craniofacial district. The aim of this study is to assess the reliability of diagnostic imaging to replace the biopsy in a district with high anatomical risk.

From 1990 to 2011 at the Department of Sensory Organs of Umberto I Policlinico, four patients affected by FB presented. Three patients presented aspecific symptoms such as nasal obstruction, headache, and facial pains; in one case, the lesion was discovered incidentally. The first patient had a lesion involving the anterior and posterior ethmoid (►Fig. 1), the second patient had a lesion involving the sphenoid and the base of the skull (►Fig. 2), the third patient had a lesion involving the mandible, and the last patient had a lesion involving the anterior ethmoid. All patients underwent CT of the head, and in all cases the radiologist did not find sufficient evidence to make a diagnosis. According to the radiologist, the authors had two choices: follow-up or biopsy. In three cases the authors decided immediately to perform a biopsy, because the anatomic site of the lesion was easily accessible endoscopically. In one case the authors had many difficulties and after conferring with the patient, the decision was made to wait and see. The choice must be made after evaluating the risk of surgery and the probability of malignant lesion. The authors reviewed the scientific literature on the imaging of FD in facial bones. We applied the following exclusion criteria: case reports, articles with no radiological description,

Fig. 2 Sagittal computed tomography scan. Expansive lesion involving the sphenoid.

and articles prior to 1980. Five articles remained and we calculated for each one the margin of error between the radiological diagnostic hypothesis and the histologic diagnosis. Amato et al studied 12 patients: 11 of them underwent CT, 1 underwent an MRI, and biopsies were performed on all 12 patients. Radiological diagnosis was disproved in four cases by histological examination (diagnostic error ¼ 36%).8 The only patient who underwent an MRI exam showed a hypointense lesion in both T1-weighted and T2-weighted images. This finding was aspecific for FD. Cappabianca et al made diagnosis of FD in 23 patients studied with CT and MRI with and without contrast. In six cases the radiological diagnosis was disproved by histological examination (diagnostic error ¼ 22%).9 Lupescu et al detected FD in all six cases they reviewed (diagnostic error ¼0).10 Alsharif MJ et al studied with CT without contrast a series of 127 patients with fibro-osseous lesions of the jaw, and proposed a radiological diagnoses of FD in 22 out of 29 patients with histological diagnosis (diagnostic error ¼ 64%).11 Worawongvasu and Songkampol studied 122 patients. Among these, 28 had radiographic features typical of FD, and histological diagnosis of FD was performed in 52 cases (diagnostic error ¼ 46.2%)12 (►Table 1). We excluded the study by Atalar et al from our literature review because it evaluated three cases of FD diagnosed only by the clinical and radiological features without performing histological examination to confirm them, as well as the study of Adada et al that diagnosed FD in eight patients only on imaging and clinical basis.13,14

Discussion Fig. 1 Axial computed tomography scan. Expansive lesion of the left ethmoid cells reaching medial wall of the orbital cavity. Evident the image of “ground glass.” Journal of Neurological Surgery—Part B

Unfortunately, CT and MRI scans provide suggestive but not pathognomonic images for this condition and, according to the literature, the likelihood of diagnostic error is not negligible.15–17 FD is characterized by the absence of


Materials and Methods


Fusconi et al.

Table 1 Fibrous Dysplasia—Review of the Literature (1983–2010) Authors

Year

N. cases

% Diagnostic error

Amato

1993

11

36%

Cappabianca

2008

23

22%

Lupescu H.

2001

6

0%

Alsharif MJ

2009

127

64%

Worawongvasu

2010

122

46.2%

pathognomonic radiological aspects mostly due to the histological variability.18–20 Three radiographic patterns have been described in FD: predominantly sclerotic (34 to 38% of cases), predominantly lytic or cystlike (11 to 22% of cases), and mixed (40 to 55% of cases).10,21 The CT aspect of FD depends on the quantity of bone and fibrous tissue and also on the mineralization degree of the pathological tissue that tends to increase with time. Typical characteristics of FD, although not pathognomonic, are areas of homogeneous gray hazy density usually described as ground-glass (►Figs. 1, 2). This aspect is due to the simultaneous presence of bone trabeculae and fibrous tissue.22 CT and MRI imaging of FD does not have pathognomonic radiological features (►Fig. 3). MRI aspects usually show an intermediate signal in both T1-weighted sequences and in PD. Images obtained with T2-weighted sequences are usually characterized by heterogeneous hypointensity.23,24 On the contrary, Jee et al examined records of 13 patients who had undergone an MRI with histological confirmation of FD, and MRI detected a high variability: only 38% of patients showed a hypointensity signal in T2-weighted MRI and 62% of patients

Fig. 3 Axial magnetic resonance imaging scan: expansive lesion of the left ethmoid cells and reaching medial wall of the orbital cavity; areas of calcification within the lesion.

showed a hyperintense signal. After administration of contrast medium, 73% of cases showed a contrast enhancement at the central level of the lesion and 27% of cases showed a contrast enhancement at the peripheral level of the lesion.25 Given that the other fibro-osseous diseases (OF, PD, OS) have no pathognomonic radiological features, it is impossible to make differential diagnosis of FD with imaging alone. CT scanning of the OF reveals an expansive lesion that shows variable attenuation and delineates surrounding osteosclerosis. In contrast with FD, the radiographic borders appear relatively smooth, round or oval, and well defined. However, the tumor may have other different and irregular shapes, so there is no radiological feature of OF that may allow a certain radiological diagnosis.26,27 The radiographic characteristics of OS have three basic patterns: no ossification, mottled ossification, and lamellar ossification. The first pattern shows a total absence of bone formation within the tumor, and CT reveals hyperdense areas with irregular edges. The second CT pattern shows irregular borders and invades the cortex, in some cases with a groundglass appearance; this radiological feature may be confused with FD. The third CT pattern shows new bone formation within the tumor, in the form of characteristic bony lamellae irradiating from a focus like a sunburst. So there are no pathognomonic radiological aspects for OS.28,29 According to Koury et al, other fibrous ossifying lesions such as the early stage of OF and OS have the same X-ray images of FD, making impossible a differential diagnosis.30 Bianchi et al also showed that the diagnosis by imaging of OS and of DF has the same difficulties with a probability of error of 30% and false positives for FD.31 Radiological images may reflect one of the three phases of PD. Lytic phase is characterized by osteolysis that is welldefined. The mixed phase is characterized by the coarsening and thickening of the trabecular pattern and cortex. The blastic phase shows marked bone enlargement and thickening. The sclerotic areas are seen as focal opacities and are described as the ‘‘cotton wool’’ appearance at radiography.32,33 Again, there are no pathognomonic radiological aspects for PD. Only a few studies used both CT and MRI. Among them, Cappabianca reported the lowest diagnostic error we found in our literature review.9 OF may have a low-signal intensity area on T1-weighted MRI and a high-signal intensity area on T2-weighted MRI. After the administration of contrast material, in OF, Journal of Neurological Surgery—Part B


Literature review


Fusconi et al.

Table 2 Computed Tomography Features of the Fibro-osseous Lesions CT

Fibrous dysplasia

Symmetry

Edges

Poorly defined

Cortical bone

Thin

Paranasal sinuses involvement Soft tissue involvement

Paget

Ossifying fibroma

Osteosarcoma

þþ

þ

Well defined

Well defined

Irregular

Thick

Thin

Cortical destruction

þþþ

þþ

þ

þ

þþþ

Ground glass appearance

þþþ

þ

þ

Cotton wool appearance

þ

þþþ

Egg-shell

þþ

þþ

Abbreviation: CT, computed tomography.

MRI

Fibrous dysplasia

Paget

Ossifying fibroma

Osteosarcoma

T1

Hypointense

Hypointense

Hypointense

Hypointense

E2

Iso-hyperintense

Hyperintense

Hyperintense the central core, hypointense the margins

Intermediate

Enhancement

No

Yes

Enhancement of the outer shell and septa

Yes

Abbreviation: MRI, magnetic resonance imaging.

enhancement of the outer shell and septa is observed, as in our case. These findings are helpful diagnostic clues in the differentiation of OF from fibrous dysplasia on MRI.34,35 MRI can characterize any soft tissue extent of OS. The signal depends on bone content of the tumor, being primarily low on T1 and intermediate on T2.17 MRI is more sensible than CT to study the marrow, so we can use this imaging technique in the study of PD. The marrow shows variable aspects depending on the disease phase and the histologic composition. Three patterns have been described: the first one, seen in the mixed phase; the second one, called ‘‘speckled’’ and seen in the lytic to early mixed active phase; and the third pattern, seen in the late blastic inactive phase. The postcontrast sequences show an increased enhancement of the involved bone, to be referred, according to Smith et al, to active disease.36 In conclusion, FD is a rare bone disorder that occurs with a wide variety of pathological conditions and is often asymptomatic. The diagnostic imaging, never standardized, plays an important role because CT and MRI images are often highly suggestive of FD but still leave many doubts in the differential diagnosis. Considering our experience and the review of the literature, there are two possible diagnostic iter: the biopsy, (this is the only procedure able to provide a certain differential diagnosis of FD) or followup (subjecting the patient to periodic radiological examinations). The decision must be weighted according to the anatomical site of the tumor, patient compliance, and clinical manifestations of the patient. CT and MRI findings are summarized in ►Table 2 and ►Table 3. Journal of Neurological Surgery—Part B

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