The aim of this study was to perform a histological analysis of the conditions in patients undergoing surgery for unilateral condylar hyperplasia (UCH) using different histopathological analytical techniques and to describe the complications and existing controversy in order to better define the disease. A partial condylectomy was performed in five patients who had been diagnosed with UCH using clinical and imaging methods. The samples obtained were analyzed using routine histological techniques including haematoxylin–eosin, Van Gieson, picrosirius, alcian blue/haematoxylin–eosin, and AgNOR staining. The analyses were performed by an observer who was blinded to the clinical parameters of the disease. The cellularity, tissue layers, size of the anatomical structures, and the relationships between them were assessed. The analysis of these patients was complemented by a review of the scientific literature. Variability was observed in the analysis of the cases. The presence of connective tissue was detected at the bone level, with cartilage formation at different levels. Each island presented levels of involvement that could indicate various degrees of aggressiveness. Type I collagen was observed in most cases, although type III was also identified. The development of histological diagnostic methods to determine the aggressiveness or level of involvement in UCH is not currently possible. Further studies are needed to establish new histological classifications.
Hyperplasia is defined as the growth of the number of cells present in a certain tissue with no increase in their size. When this affects the mandibular condylar head, it is called condylar hyperplasia (CH) and is characterized by alterations in both the condylar and facial morphology.
Classifications have been developed in an attempt to standardize the concept of CH and its treatment, establishing a series of parameters associated with its clinical presentation and the conditions of diagnosis and treatment. Classification systems related to the clinical presentation, imaging characteristics, and functional aspects have also been proposed. The classification proposed by Slootweg and Müller includes limited histological aspects within the parameters ; they established that different degrees of invasion of fibrocartilage islands are associated with the degree of aggressiveness of CH, classifying this from level 1 to 4.
Saridin et al. recently performed a histopathological study of unilateral condylar hyperplasia (UCH) using the classification proposed by Slootweg and Müller. They reported that the identification of the four condylar layers at the histological level using haematoxylin–eosin is complex, and only two layers were used (the four initial ones were condensed) in order to identify them with greater clarity. The patterns described by Slootweg and Müller, Saridin et al., Eslami et al., and Villanueva-Alcojol et al. have not varied significantly in their histological descriptions. On the other hand, diagnosis assisted by histology, single photon emission computed tomography (SPECT), and clinical conditions has been reported.
Wurgaft and Montenegro have stated that ascertaining the growth mechanism of the mandibular condyle at the tissue level is useful in achieving a good diagnosis and in implementing an appropriate treatment protocol that respects and guides tissue development. The aim of this study was to perform a histological analysis of a case series of five patients with CH type 1B (UCH) and to determine its characteristics using different histopathological analytical techniques. A discussion of the histological diagnosis in relation to that reported in the international literature is also presented.
Materials and methods
A descriptive study of a series of cases was performed. This research was conducted in the division of oral and maxillofacial surgery and the centre for morphological and surgical studies of the study institution in Temuco, Chile. The study was approved by the research ethics committee of the study university and was performed in accordance with the ethical guidelines established in the Declaration of Helsinki. All of the patients agreed to participate in the study.
Diagnosis and surgical procedure
Five patients aged between 15 and 18 years (three female and two male), who underwent a high or proportional condylectomy following a diagnosis of UCH (CH 1B ) were included in the study. The methodology for diagnosing and treating the subjects has been reported previously and followed the sequence described by Olate et al. ; clinical studies including facial and dental analyses, cone beam computed tomography (CBCT) for the analysis of the condyles, and SPECT were used to diagnose the progressive facial asymmetry associated with active UCH. Clinically, the patients presented a chin deviation greater than 5 mm towards the contralateral side, with a posterior crossbite and an absence of joint pain symptoms. Only in one case did the maxilla present a maxillary cant of 2 mm. The gonion of the hyperplastic side was lower than on the contralateral side in all of the subjects.
Partial resection of the condylar head was performed under general anaesthesia by the same surgeon using a pre-auricular or endaural approach and a condylar head osteotomy, which was conducted using an ultrasound system (Piezotome 2; Satelec Acteon, Acteon Group, Paris, France). All patients underwent subsequent orthodontic treatment. Some were enrolled for treatment with orthognathic surgery, while others were treated exclusively with corrective orthodontics.
The resected hyperplastic condyles were fixed immediately in 10% buffered formalin for 48 h, decalcified in 10% ethylenediaminetetraacetic acid (EDTA) buffer solution for a period of 2 months, dehydrated in a series of increasing alcohol concentrations, and embedded in paraffin (Histosec; Merck Millipore, Darmstadt, Germany). Sections 3 μm thick were obtained from the blocks using a Microm HM355S rotary microtome (Microm International, Walldorf, Germany). These were stained with haematoxylin–eosin, Van Gieson, picrosirius, and alcian blue (pH 2.5)/haematoxylin–eosin, as well as undergoing staining of the argyrophilic nucleolar organizer region (AgNOR) to observe argentaffin proteins. The slides were viewed under a Leica microscope and photographed with a Leica ICC50 HD camera (Leica Microsystems, Heerbrugg, Switzerland). The presence, extension, and characteristics of the tissue layers comprising the condylar surface were assessed according to the description by Wurgaft and Montenegro.
The analyses were performed by an observer who was blinded to the clinical parameters of the disease.
The histological analysis showed differences in condylar architecture ( Table 1 ). In the area of greatest pressure, all of the condyles presented a well-defined surface and proliferative and fibrocartilaginous layers. However, the extension and thickness varied across the condylar surface. Clinically, the only patient who presented maxillary involvement in the facial asymmetry was case 3; the others exclusively showed facial asymmetry with chin deviation and a unilateral posterior crossbite (contralateral to the hyperplastic condyle).
|Case||Age (years)||Sex||Affected side||Number of layers of the articular surface||Compact bone tissue||Picrosirius polarization staining method||Cartilage islands a||Alcian blue pH 2.5 a||AgNOR a|
|1||15||Male||R||4||Present, discontinuous||Abundant type I collagen was observed in all layers of the articular surface and in the compact and spongy bone; type III collagen was observed mainly in the fibrocartilage layer and trabecular bone||+++||++||+++|
|2||18||Female||L||3 b||Absent||Type I collagen was distributed mainly in the surface layer and trabecular bone; type III collagen was present in greater amounts in the interface of the proliferative and fibrocartilaginous layers||+++||+||+++|
|3||17||Female||L||4||Present, discontinuous||Type I collagen was found in all layers of the articular surface in different proportions; type III collagen was present in greater amounts in the surface layer and trabecular bone||+||+||++|
|4||17||Male||R||4||Present, discontinuous||Type I collagen was distributed in large amounts throughout the condylar structure; type III collagen was observed mainly in the thick surface layer and in greater amounts in the proliferative layer||±||−||+|
|5||16||Female||R||4||Present, discontinuous||Type I collagen was observed mainly in the fibrocartilage layer and trabecular bone furthest from the articular surface; type III collagen was observed mainly on the surface and proliferative layers and the outermost bone trabeculae||+||−||+|
In this patient, the right side was compromised ( Fig. 1 ). The surface layer was observed to be larger in the superior area of the condyle compared to the lateral areas ( Fig. 2 A) . The cellular component was present, and type I collagenous fibres were arranged parallel to the articular surface in the outer area and, to a lesser extent, in all directions in the deepest area ( Fig. 2 B).
The surface layer was also thicker in the central area of the condyle, with abundant cellularity ( Fig. 2 A) and a transition towards the not very well-defined fibrocartilaginous layer. A small number of collagenous fibres were observed and picrosirius staining revealed these to be mainly type I ( Fig. 2 B).
In the fibrocartilage layer, hyperactivity was detected in the zone of probably the greatest compression, with some interruptions in the bone plate and penetration of hypertrophic chondroblastic cells towards the medullary bone component of the mandibular condyle ( Fig. 2 A). Cartilage islands were observed in the trabeculae of the medullary bone with a positive reaction for alcian blue pH 2.5 and with surrounding osteoblastic activity ( Fig. 2 C).
Silver staining revealed many AgNOR points scattered throughout the nuclei of the cells of the proliferative layer and of the chondrocytes of the fibrocartilaginous layer that were in the outermost area ( Fig. 2 D). The hyperplastic chondrocytes showed a minor presence of AgNOR points. Some chondrocytes with AgNOR points were observed at the trabecular level of the medullary bone of the condyle.
In this patient, the left side was involved ( Fig. 3 ). The proliferative layer was thicker, probably in the area of greatest pressure. It showed abundant cellularity with undifferentiated mesenchymal cells on the surface and small, flattened chondrocytes with nuclei parallel to the surface, whereas deep down they appeared larger and rounded ( Fig. 4 A) . Type I collagenous fibres were observed in very small numbers, scattered mainly parallel to the surface ( Fig. 4 B).
The fibrocartilage layer appeared rather like hyaline cartilage, with greater thickness in the area of greatest pressure and presenting an abundant number of hyperplastic chondrocytes. Medullary spaces of cancellous bone were in direct contact with the overlying cartilage ( Fig. 4 A). The type I collagenous fibres were perpendicular to the surface ( Fig. 4 C).
AgNOR points were observed in the nuclei of the cells of the proliferative and cartilaginous layers; nevertheless, in the latter the silver staining was observed mainly in the most superficial chondrocytes. Only some chondrocytes presented AgNOR points. There were also some chondrocytes with AgNOR points in the medullary bone trabeculae ( Fig. 4 D).
The condyle in this patient had four well-defined layers across the condylar surface ( Fig. 5 A) . The surface layer was thickest in the central area of the condyle, with organized type I collagenous fibres parallel to the surface and in all directions in the deepest area ( Fig. 5 B, C). Type III collagenous fibres appeared in smaller quantities ( Fig. 5 B). Of note, some chondrocytes were observed on the surface area of this layer ( Fig. 5 C).
The proliferative layer displayed abundant cellularity and scant extracellular matrix; this differentiated it easily from the underlying fibrocartilaginous layer, which was constituted of chondrocytes immersed in an extracellular matrix rich in type I collagenous fibres scattered in different directions.
The layer of calcified cartilage made it easy to differentiate the connective tissue that covers the condyle from the condylar bone tissue; the latter comprised mature compact lamellar bone tissue. Silver staining showed AgNOR points in the nuclei of the cells of the proliferative and fibrocartilaginous layers ( Fig. 5 D).
In this case, the layers were continuous and varied in thickness according to the area in which they were found, being thicker in the central area ( Fig. 6 A) . The surface layer appeared thicker. Type I collagenous fibres were dispersed in groups parallel to the articular surface and in multiple directions in the deepest area ( Fig. 6 B).