The three‐dimensional reverse face (3D RF) view for the diagnosis of cleft palate

Orofacial clefting (CL/P) is among the most common of congenital abnormalities, with an incidence of nearly 2/1000 births1. Because they arise from different embryological tissues, clefts of the lip (CL) and primary palate i.e. the alveolus and palate to the incisive foramen (CLA) can occur independently of clefts of the secondary palate (CP) and vice versa. In Denmark isolated CP accounts for 25% of the total cases of CL/P but surveys in other countries show that this rate varies and it has been reported to be over 50% in some European countries2-4. CL and CLA can be lateral, bilateral and medial and are due to a variety of failures of fusion of the maxillary swelling with the medial nasal process. CP is always midline and is the result of failure of the palatine processes to elevate or grow. The prognosis for CLA is also very different from that of CP, which is significantly more associated with difficulties of speech, hearing and feeding and (following surgery) mid-face protrusion. The majority of cases are multifactorial so prenatal diagnosis will primarily depend on careful screening with ultrasound. The effectiveness of screening for CL/P by ultrasound varies widely between series. Stoll et al.5 described how a systematic approach improved the detection rate of facial clefts from about 5% between 1979 and 1988 to over 26% during the years 1989–1998. Nevertheless, the rate of diagnosis of isolated CP is extremely low6 as a palatal defect will not be recognized on the standard oblique-face view that is routinely used to assess the upper lip and alveolar ridge, because shadowing of the palate by the densely bony ridge makes visualization difficult. Even the introduction of 3D technology which has improved the detection of CLA7-9 does not appear to improve visualization of the secondary palate10. In this issue's Picture of the Month we show an image of CP visualized using a new ultrasound technique, the three-dimensional (3D) reverse face (3D RF) view which overcomes problems of shadowing and is simple, rapid and appears to be effective in visualizing the palate and palatal defects. We have carried out investigations using this technique with the GE Voluson 730 ultrasound machine (GE Medical Systems, Bedford, UK) which has two-dimensional (2D), 3D and four-dimensional (4D) facilities. To obtain a high-resolution image a 4D capture using a slow frame rate (2.7 MHz) or a 3D sweep is used. The harmonic setting is usually employed for better interface definition. The fetal face is visualized by obtaining a 2D profile or near profile and the volume box adjusted to encompass the complete facial outline and cranium. The viewbar is adjusted to provide an optimized surface-rendered image of the face. The lips are examined and the viewbar is then scrolled through the lips until the alveolar ridge is identified. Further movement of the viewbar through the face to identify the palate usually results in a severely shadowed image which is diagnostically unhelpful and may be misleading. The 3D RF view overcomes this problem. A return to the frontal view of the face is made and the face is rotated through 180°. This provides an unobstructed view of the retrofacial area. The viewbar is then scrolled through the length of the palate. It is important that a true coronal plane is obtained. This is ensured by minor adjustments to the rotational axis so that both eyes are symmetrically placed in the upper part of the image with the nasal cavity in the midline between and just below the eyeballs. In the normal case, the intact palate will be seen as a distinct line separating the nasal and the oral cavities (Figure 1). Ultrasound image of a normal fetus using the three-dimensional reverse face view: the nasal cavity is situated between and just below the symmetrically placed orbits, and the intact palate is seen as a distinct horizontal line separating the nasal and the oral cavities. The 3D RF technique is rapid and highly effective from 20 weeks' gestation onwards. From the obtaining of the frontal view of the face to the completion of visualization of the palate takes 2 or 3 min. The patient in our Picture of the Month was referred at 31 weeks because a 2D scan 3 weeks previously at a tertiary center had diagnosed bilateral CL with major clefting of the alveolus. These findings were confirmed on 3D scanning (Figure 2). In addition the 3D RF view demonstrated a large defect in the secondary palate. The edges of the cleft in the secondary palate were obscured by the tongue which was partially elevated into the nasal cavity (Figure 3). The infant was delivered spontaneously at term and had a bilateral CLA and a large palatal defect. The CL was repaired 3 months after birth with partial closure of the hard palate, i.e. complete left vomerine flap, nasal floor reconstruction and a limited flap on the right side; full repair will be carried out at the age of 7 years. Three-dimensional ultrasound image (frontal view) of the affected fetus showing the bilateral cleft lip. Ultrasound image of the affected fetus using the three-dimensional reverse face view: the margins of the cleft in the secondary palate were obscured by the tongue, which has a corrugated echogenic appearance and was partially elevated into the nasal cavity. There are still problems to be overcome in the diagnosis of CP by this technique. At present the Voluson 730 does not permit measurements to be made in the surface-rendered modality. This makes it difficult to give the surgeon a precise estimate of the size of the palatal defect although a gross estimate (wide or narrow) can be made. Protrusion of the tongue through the defect also can obscure the edges of the cleft but the tongue is clearly identifiable as it is more echogenic than surrounding tissues and when protruding through the cleft it has a corrugated appearance. Any lesion with significant tongue protrusion is certain to be large. It is also difficult at the present time to know whether defects of the velum (soft palate) can be identified. Despite these problems, it appears that surface rendering of intracranial structures by the 3D RF view can provide unique diagnostic information on the integrity of the secondary palate.