Combined Hemimandibular Hyperplasia and Elongation: the Orthodontic-Surgical Management

Case report

An 18-year-old male presented with complaints of facial asymmetry. Medical and social histories were non-contributory. Examination revealed a Class II division 1 incisor relationship on a Class II skeletal base complicated by a left-sided lateral open bite of 9 mm and a deviation of chin point to the right by 2 mm.

Clinical and radiographic examination confirmed a diagnosis of combined hemimandibular hyperplasia and elongation (Figures 1−7). Condylar growth was assessed as inactive by the use of nuclear medicine scans. Three dimensional computed tomography was used for pre-surgical planning.

The patient underwent a course of pre-surgical orthodontics for alignment and decompensation which took 18 months as it included exposure and alignment of an impacted upper left canine. Orthognathic surgery was performed both to close the lateral open bite and improve aesthetics. (Figures 4 and 6). This involved a Le Fort 1 segmental osteotomy with impaction of 5 mm on the right and a segmental cut between UL3 and UL4. To impact the mandible, an inverted “L” ramus osteotomy on the left side and a sagittal split osteotomy on the right side was carried out. In addition, a closed rhinoplasty to reduce the nasal hump and a genioplasty was completed to improve facial profile and correct asymmetry. The patient was placed into postsurgical elastics for one month. Despite a minimal bilateral lateral open bite, a favourable aesthetic and functional outcome was achieved post-operatively which remained stable for 12 months following surgery (Figures 5 and 6).

Discussion

Hemimandibular Hyperplasia, Hemimandibular Elongation and Hybrid subtypes were first described as distinct entities by Obwegeser in 1986.³ Condylar Hyperactivity is the collective term used to describe these three subtypes.² Unfortunately, this term is commonly confused for Condylar Hyperplasia despite Obwegeser separating these conditions into separate entities with distinct clinical and radiographic features.³ This misconception in the literature makes it difficult to identify the true epidemiological characteristics of this condition.¹

The aetiology of CH remains unknown. Several potential aetiological factors have however been proposed; trauma, infection, genetic conditions, increased functional loading of the TMJ, hormonal influences, arthrosis, and hypervascularity.⁶

HH and HE have specific clinical and radiographic features which are summarized in Figure 1. The Hybrid subtype is a combination of features from HE and HH and the presentation is determined by the influence of each underlying condition. Abnormal mandibular growth can lead to skeletal asymmetry, malocclusion and masticatory, phonetic and psychological problems, therefore treatment is generally indicated.⁷

Orthodontists play an important role in the management of CH. Facial asymmetry is common and can be considered a normal variation, however, once the asymmetry lies outside the normal range, it begins to be noticed by patients and their family and friends and is attributed with functional problems.

Once a facial asymmetry has been identified, it is important to diagnose its aetiology accurately to exclude any potential sinister causes.⁸ Differential diagnoses are summarized in Table 1.

A degree of deviated occlusal cant and visible one-sided asymmetrical enlargement of the mandible, should be an indication for further management.¹ A full examination should be completed including a family, medical, social and dental history to help identify any contributing factors. Special investigations can assist with diagnosis of this condition (Table 2). Bone scans in conjunction with a clinical examination remains the current gold standard for diagnosis.⁹

Once a diagnosis of CH has been made, the activity of the condition needs to be determined in order to treatment plan effectively. A number of methods are employed to evaluate the activity, asymmetry and progression of condylar hyperactivity.^10,11 Nuclear medicine imaging is relatively accurate at differentiating normal from abnormal bone growth and therefore identifying a cause of asymmetry;¹⁰ Single-Photon Emission Computed Tomography (SPECT), Positron Emission Tomography (PET) or Bone Scintigraphy with radionuclide dye are the most commonly used methods. Other aids include articulated study models, plain film radiographs/computed tomography, optical scanning, photography or stereophotogrammetry. Negative effects of all of these modalities must be weighed against the diagnostic benefits of the test.

A variety of treatment options for HH, HE and Hybrid forms have been reported (Table 3). The treatment of choice is debatable and varies among different clinicians. Consequently, a number of factors must be taken into consideration including patient complaints and expectations, clinical progression and severity of the deformity prior to treatment planning (Figure 2).

Once condylar growth is considered inactive for a period of time (usually six to twelve months) a definitive treatment plan can be formulated. Treatment is primarily surgical and is complemented by orthodontics to correct malocclusions.

Conclusion

Patients with orofacial deformities and asymmetries can provide a real challenge from the treatment perspective. It is important that these patients are managed within a multidisciplinary setting, taking into consideration patients' wishes. There is a risk of relapse with these patients and therefore a long-term follow-up is essential

Our patient has had a favourable aesthetic and functional outcome, which is still present 12 months post-operatively. This patient remains on long-term follow-up.

Although condylar hyperactivity is rare, it requires an accurate and prompt diagnosis. It is essential that Orthodontists are aware of this condition to ensure an accurate and early referral to minimize complications and improve treatment outcomes.