The adenoidal-nasopharyngeal ratio (AN ratio)

The Journal of Laryngology and Otology June 1987. Vol. 101. pp. 569-573

The adenoidal-nasopharyngeal ratio (AN ratio) Its validity in selecting children for adenoidectomy by SAMY ELWANY,

M.D. (Al Khobar, Saudi Arabia)

Many otolaryngologists and pediatricians maintain that the methods employed clinically for estimating the size of adenoids are in many ways unsatisfactory. Hibbert et al. (1980), in a well designed study, found that symptoms and signs are very unreliable predictors of adenoid size, and that it is incorrect to base the decision for adenoidectomy on clinical findings only. In another report, Maw et al. (1981) found poor inter-observer agreement for the clinical assessment of the condition, and attributed their findings to differences in the clinical experience of the examiners. The feeling that clinical assessment alone can be misleading when a decision for adenoidectomy has to be taken stimulated the quest for a radiological means of confirming the diagnosis. Several radiological techniques have been suggested (Weitz, 1946; Johannesson, 1968; Pruzansky, 1975; Hibbert and Whitehouse, 1978). However, their use in routine daily practice has not been popular since the interpretation of radiographs has varied from author to author, and there has always been a divergence of opinion as to what constitutes abnormally large adenoids. Moreover, some of these techniques are expensive and unavailable in rtfany medical centers. The adenoidal-nasopharyngeal ratio was first described by Fujioka et al. (1979), who measured it in a large series of normal children. The present work set out to measure the AN ratio in children selected for adenoidectomy and to assess its reproductibility between different observers and its predictive reliability in determining candidacy for adenoidectomy. Material and methods Subjects: One hundred children scheduled for ade-

noidectomy were studied. There were 68 boys and 32 girls in the age range 3-7 years. As a control group, one hundred normal children, matched for age and sex with the first group, without known ENT abnormality were also examined. The consent of the parents of all children was obtained. Clinical assessment: Clinical assessment was made by three observers. A history of snoring, from parents, was recorded as absent (0) or present (I). Each child was then assessed for mouth breathing and hyponasality. Each observer scored a sign when present as I and when absent as 0. The scores of each child were added together to give the clinical assessment score (CAS). Radiographic assessment: Lateral radiographs of the nasopharynx were exposed with the patient in the erect position and the head fixed with a wallmounted cephalostat and oriented with the Frankfort horizontal plane. The exposures were made with 100 kv. and 50 raA. The exposure time varied between 0.4-0.6 sec 569

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depending on the age of the child. The tubecassette distance was 180 cm. With this arrangement, the median plane is enlarged by 65 per cent. The adenoidal measurement A represents the distance from the point of maximal convexity of the adenoid shadow to a line (B) along the anterior margin of the basiocciput.

The nasopharyngeal measurement N is the distance between the posterior border of the hard palate (p) and the antero-inferior edge of the sphenobasioccipital synchondrosis (S). When the synchondrosis is not clearly visualized, the point S is determined as the point on the anterior edge of the basiocciput which is closest to the intersection of lines A and B (Fig. 1). This has been found to be an easier landmark than Fujioka's original landmark of the point of crossing of the posterior border of the pterygoid plate and the basiocciput. The AN ratio was obtained by dividing the measurement for A by the value for N. All measurements were made with a caliper to within ± 0.1mm. Each' radiograph was assessed by three observers and the mean value of the AN ratio was determined for each case. Agreement between observers was considered absolute when the AN ratio values of the three observers were identical (within 0.1), relative when two were identical, and lacking if the three were different. An overall impression of the size of adenoid and nasopharyngeal airway was scored by assessing the radiographic adenoid shadow incrementally as small or normal (0), moderately enlarged (I), or markedly enlarged (2). The nasopharyngeal airway was rated normal (0), moderately narrowed (I) or markedly narrowed (2). These scores were combined to give the radiological assessment score (RAS). The average score was calculated for each case. The inter-observer agreement was considered absolute if the three observers were identical (within 1 scale point), relative when two observers were identical, and absent if the three were different.

1 Measurements for calculation of the AN ratio on standard lateral skull radiograph. Line B is tangential to the basiocciput. The adenoidal measurement (A) is obtained by drawing a prependicular line to B at the point of maximal adenoid tissue. The nasopharyngeal measurement (N) is made between the posterior border of the hard palate (P) and the antero-inferior aspect (S) of the spheno-basioccipital synchondrosis (white arrowheads). When the synchodrosis is not visible the point (S) is determined as the point on the anterior edge of the basiocciput which is closest to the intersection of lines A and B. The black arrowheads outline the adenoid shadow.

Adenoid weight: One surgeon performed all of the adenoidectomy operations by a standard curettage technique. Immediately after removal the tissue was washed, and weighed using a chemical beam balance. The weights were recorded.

FIG.

Results /—Measurement of the AN ratio: The mean AN ratio for children selected for

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THE ADENOIDAL-NASOPHARYNGEAL RATIO TABLE I AN RATIO VERSUS CLINICAL ASSESSMENT OF ADENOID SIZE

AN ratio Adenoid size Mean ± SD

Range Normal Moderately enlarged Markedly enlarged

0.499-0.621 0.593 + 0.0771 0.652-0.742 0.680 + 0.1028 0.732-0.853 0.726 ± 0.1007 TABLE II

CORRELATIONS OF AN RATIO, CAS, RASi, AND ADENOID WEIGHT

AN ratio

CAS RAS Adenoid weight

r

t

P

0.72 0.21 0.66

10 .52 2 .13 8.69