Mandibular Deformity in Hemifacial Microsomia

Sir: We read with interest the article entitled "Mandibular Deformity in Hemifacial Microsomia: A Reassessment of the Pruzansky and Kaban Classification," by Wink et al.1 Our group began classifying hemifacial microsomia in a retrospective study of the natural history and progression of the deformity in untreated patients. We concluded that the severity of end-stage facial asymmetry was predicted by the mandibular type2 as designated in Pruzansky's original classification.3 Subsequently, the criteria for type II deformity were modified for surgical planning4: Wink et al.1 call this the Pruzansky and Kaban classification. The purpose of their study was to use three-dimensional computed tomography to categorize the mandibular deformity in 38 hemifacial microsomia patients. They conclude that three-dimensional imaging highlights inaccuracy and variability of the Pruzansky and Kaban schema and suggest the need to "reexamine the classification of hemifacial microsomia," presumably referring to the mandibular component. We find flaws in the design and methodology of their research.1 First, their standard was the senior author's typing of the deformity based on physical examination alone. The Pruzansky and Kaban classification requires both physical examination and imaging. Clinical typing of an infant or toddler is the first step and should be confirmed or revised after obtaining radiographs in childhood. Second, typing by three-dimensional imaging only tested the participants' "understanding of the Pruzansky and Kaban criteria" and not the validity or reproducibility of the system. To accomplish the latter, participants would have to be trained and tested in mandibular typing. Their average of 15 years' experience does not ensure that the Pruzansky and Kaban system was used correctly. The low correlation rate (39 ± 8.6 percent) is not surprising without initial imaging and confirmation of interrater reliability. Third, even the authors' description of Pruzansky and Kaban typing is inconsistent and sometimes inaccurate. In Figure 1, type IIA is defined as follows: "The mandibular ramus, condyle and temporomandibular joint are present but hypoplastic and normal in shape." This statement is incorrect. Type IIA is defined as a hypoplastic mandible that is abnormal in shape. In the same figure, the below, left panel is mislabeled type IIB (it is bilateral type III) and the below, right panel is mislabeled type III (it is type IIB). The authors criticize the Pruzansky and Kaban system because three-dimensional imaging prompted a change; in some cases, from type I to IIA and IIA to IIB or the reverse. On the contrary, such reassessments are expected. Their proposed categories—mild (I), moderate (IIA), and severe (IIB and III)—are analogous to our original groups.4 For treatment purposes,4 we separated patients with types I and IIA (mild and moderate) as group 1 and types IIB and III (severe) as group 2. The surgical significance is the same in both articles.1,4 Types I and IIA have sufficient bone stock and an adequate temporomandibular joint for distraction osteogenesis or osteotomies, often without bone grafts. Types IIB and III (group 2) require construction of the ramus/condyle unit and sometimes the temporomandibular joint. A classification system should aid in diagnosis of a condition, improve communication among clinicians, help predict progression of disease/deformity, and guide research. The Pruzansky and Kaban typing system is alive and healthier than ever with the aid of three-dimensional imaging and a new moniker by Wink and colleagues. Unfortunately, the authors fell into the intellectual trap described by eighteenth century Irish theologian George Berkeley: They "… first raised a dust and then complain we cannot see."5 DISCLOSURE The authors have no financial interest to declare in relation to the content of this communication. Leonard B. Kaban, D.M.D., M.D. Bonnie Padwa, D.M.D., M.D. John B. Mulliken, M.D. Massachusetts General Hospital Boston Children's Hospital Boston, Mass.