Dear Editor,
Emergency indications for obtaining head and neck CT in a newborn are very few. Choanal atresia is one such condition. It is the anatomical closure of the posterior choanae in the nasal cavity leading to non-communication between the nasopharynx and the nasal cavity. Although the actual incidence of the abnormality is low, it is the most common congenital anomaly associated with the nose. The clinical picture can be varied, depending on whether the abnormality is bilateral or unilateral, along with the presence or absence of other associated congenital abnormalities [1].
Initial clinical evaluation consists of passing a six or eight Fr suction catheter via the nostrils, the inability to do so represents a possibility of choanal atresia. Nasal endoscopy can also be used to visualise the site of actual obstruction. CT scan is considered the gold standard for pre-operative diagnosis.
A common pitfall that we have observed on CT imaging in these patients of choanal atresia is the presence of thick tenacious mucous secretions in the nasal cavity, which, in the presence of unossified anterior skull base in neonates, can mimic the presence of an anterior encephalocoele [2, 3]. At birth, the anterior skull base is largely cartilaginous, and complete ossification may take as long as 2 years. Ossification starts peripherally at about 2 months of age, and then proceeds towards midline [4].
Suctioning of these secretions prior to CT can help avoid this misdiagnosis. In cases of persistent diagnostic dilemma MRI can prove to be a valuable troubleshooting tool. However, MRI is costly, time consuming and often requires sedation.
We encountered two such cases in recent past, and present the representative images of one. In both, diagnostic confusion arose due to presence of thick nasal secretions in the presence of unossified cribriform cartilage. On initial evaluation, the attenuation of the nasal contents being similar to brain parenchyma on a non-contrast scan led to a misdiagnosis of co-existent encephalocele (Fig. 1). However, altering the image window and multiplanar reformats helped identify the intact dura, thereby excluding encephalocele.
Fig. 1.
A–E Axial NCCT bone window image reveals bilateral membranous choanal atresia (arrows) with retained secretions (asterisk).Coronal (B) and sagittal (C) reformatted NCCT images show the hyperdense nature of the contents, and intact frontal lobe dura (arrows). Coronal heavily T2W MR CISS image (D) reveals intact T2W hypointense dura (arrow). Axial CISS image (E) shows the retained secretion on the right side is hyperintense (dotted arrow), and that on the left is hypointense (asterisk) owing to its high protein content
Since the implications of making such an additional diagnosis is paramount; the radiologists as well as paediatricians should be well aware of this pitfall, and interpret cautiously.
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References
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