The monostotic, craniofacial type of FD is a rare type that occurs in approximately 25% of cases and is limited mostly to the bones of the viscerocranium or neurocranium. Fibrodysplastic changes are most often located in the maxilla and mandible, and a negligible percentage of cases are located in the zygomatic bone and may pass through the sutures [14, 21–24]. The lesions initially occupy one bone of the face, and consequently, over time, they usually progress to adjacent bones through continuity.
The classification and categorization of FD has been widely discussed by various researchers for many years, as there is no clear and precise criteria for monostotic or polyostotic forms [25–32].
Daves and Yardley described the craniofacial type of FD as the type usually involving two or more bones in the skull [33]. Similarly, Eversole et al. and many other authors included craniofacial dysplasia in the polyostotic group because they believe that this variety usually affects many bones of the skull, even if only one bone is involved at a time [28, 29, 31, 33].
Gupta et al. proposed that when craniofacial FD covers a single anatomical region with bone continuity, even if it is separated by sutures, it can be considered monostotic if there is no other altered or affected bone in the body [11]. Conversely, if two separate anatomical regions of the craniofacial bones are involved, it can be classified as polyostotic craniofacial FD, whether or not any other bone is involved. In addition, when FD involves the mandible and temporal bones, it should be classified as polyostotic craniofacial FD [11, 28].
In the current case, the pathological fibroblastic changes affected only the maxilla up to the zygomaticomaxillary suture, which may correspond to the monostotic variant of craniofacial FD. However, when retrospectively reviewing the CT images, the ground glass opacity was found to be poorly marked in the ipsilateral zygomatic bone and only slightly marked in the greater wing of the contralateral sphenoid bone and the bilateral mandible heads, corresponding more to the polyostotic variant.
FD lesions may be described as quiescent, nonaggressive, or aggressive and may be associated with pain, paresthesia, pathological fracture, or malignant transformation [34, 35]. This aggressive type of transformation is extremely rare and occurs in less than 1% of all FD cases. However, cancer is more likely to occur in polyostotic disease, and the most common malignant histological types are osteosarcoma, fibrosarcoma and chondrosarcoma [2, 36, 37].
The CT scans can assist in the diagnosis and assessment of both bone and soft tissue details and are considered standard in the diagnosis of FD. In some cases, the CT examination may not be sufficient, as in the present case, when the CT examination raised doubts and did not provide an unambiguous, final answer [9–11, 14–19]. The CT images of the presented case showed a very heterogeneous mass-like lesion. There was discontinuity and a loss of the cortical layer in the anterior part of the pathological mass with features of infiltration of adjacent tissues, suggesting that it may have been a malignant lesion. However, the biopsy and histopathological examination clearly showed FD.
Therefore, it is recommended to deepen the diagnosis by performing an MRI examination. MRI can provide detailed information on soft tissues and is considered more sensitive to pathological changes, especially the nerves, vessels and other soft tissues, than CT. However, this is not always the case with FD. Sometimes, MR images are also difficult to interpret and raise doubts in the case of FD [11, 12, 19].
Usually, the clinical and radiological signs and symptoms of craniofacial FD depend on the advancement of the process and the amount of bone matrix within the lesion; there are cystic, sclerotic and mixed forms. In the earliest form, more or less clearly delimited osteolytic defects appear within the bone, and the boundary between spongy and compact bone becomes blurred. The periosteum is usually not affected [15, 38, 39].
With time, due to improper mineralization of dysplastic changes, seizure of the bone structure and improper arrangement of the bone trabeculae appear, which is described as orange peel or cotton wool [16]. The phase in which the trabeculae are completely destroyed is called sclerotic or densifying. The radiological image is usually described as ground glass changes [39]. In the late stage of the disease, areas of both thinning and thickening of the bones typical of the mixed phase are visible [8].
FD can also be a symptom of various syndromes, such as McCune–Albright syndrome or Mazabraud syndrome. The first of these manifests as a triad, next to the polyostotic type of FD, with discoloration of the skin such as coffee-with-milk type (cafe au lait) and disorders of the endocrine system [40]. This syndrome has a low gender predisposition with a slightly lower predilection for females; however, puberty disorders in patients with this syndrome are much more common in women [41]. Mazabraud syndrome is a disorder characterized by FD that can develop in a single bone (monostotic) or in multiple bones (polyostotic) and single or multiple intramuscular myxomas [42].
The etiology of FD is not fully explained, but today, the most popular idea is that it might be connected with a mutation in the GNAS1 gene that is responsible for coding the subunit Gsα of the stimulatory G protein, and its locus is on chromosome 20q13.2–13.3 [43, 44]. As a result of these postzygotic mutations, the arginine residue amino acid is replaced with either a cysteine or a histidine amino acid [45, 46]. Dysplastic features are revealed in all cells affected by this mutation. Depending on the location of the mutation in the cell mass and the size of the cell mass during embryogenesis when the mutation occurs, the clinical presentation differs [44].
Clinically, craniofacial FD usually manifests as a slow growing, painless swelling mass that may lead to facial asymmetry and deformities, as was presented in the current case.
Usually, treatment of the maxillofacial form of FD includes extensive surgery and secondary reconstruction of tissue loss, sometimes supported by pharmacological treatment with bisphosphonates.
Reconstructions of postresection cavities covering a large area of the craniofacial region are a challenge for surgeons due to their specific location, especially taking into account the psychological and technical aspects. The reconstructive method should be predictable and safe, guaranteeing the best aesthetic effect. The ideal solution is the use of a personalized, titanium 3D anatomical implant, perfectly reproducing the missing tissues thanks to the use of the mirror technique, while shortening the surgical procedure as much as possible.
A wide and extensive resection of altered fibrodysplastic bone along with reconstruction using autogenous bone grafts was first described in the 1950s and later developed in the 1970s [5].
Interestingly, in the research carried out by Collins and Curzon, the removed fibrodysplastic bone was used as an autogenous graft for reconstruction, even though the bone was pathologically altered. Their research showed that the transplanted, pathologically remodeled bone stimulated osteogenesis and could substitute a creeping graft after resection [47]. Subsequently, methyl-methacrylate implants were reported as an alternative method in reconstruction. Historically, these kinds of implants have been fairly well tolerated. Clinical results indicate high quality and lower incidence compared to the other methods [5].
Over the following years, various materials have been used for reconstructions of craniofacial defects. Among other methods, autogenous or chondrocostal grafts have been used, followed by titanium meshes, and other alloplastic materials have been proposed. Currently, titanium mesh or 3D titanium personal implants are increasingly used around the world in surgical operations due to their corrosion resistance, low density, high rigidity, and good biocompatibility [48]. Of course, surgical materials are validated before they are approved for use in surgery.
For many patients, designing and printing custom implants has become a reality and the only solution [49]. The advantages of such personalized 3D implants are the possibility of mapping a perfect, complex shape, obtaining a stable reconstruction, and increasing the accuracy of skeleton rebuilding, which in turn reduces the risk of mismatch between allografts and prostheses and the patient’s bone. The great and decisive advantage over other therapeutic methods is the perfect regeneration and recovery of tissue in a maximally shorter operation time. Additionally, there is no need to find and prepare a donor tissue location, as in the case of autografts [50]. In the present case, after removing the tumor along with the orbital floor, the bones were reconstructed with an alloplastic, specially prepared personalized titanium implant under conditions of absolute sterility. The excellent aesthetic effect of the face and the ideally perfect support of soft tissues prove that thanks to this technique, it is possible to combine the effectiveness of the treatment with its duration. As a consequence, patients have a reduced risk of tissue infections, and the maximal therapeutic effect is obtained. The disadvantage of making a personalized 3D facial implant is its relatively high cost, requiring individualized valuation of the surgical procedure and the long time necessary to design the implant itself. Additionally, excellent cooperation with the technical and laboratory teams is essential.
Despite all these difficulties, 3D reconstruction is the method of the future. Individually personalized 3D implant templates combined with the use of increasingly popular 3D printers and biocompatible materials allow for the preparation and printing of any model for an individual patient in laboratory conditions. Prepared in such a way, a unique personalized implant model can then be implanted into the patient by maxillofacial and reconstructive surgeons.