Discussion
We have reported three cases in which CT imaging of patients with OE/NOE was wrongly interpreted due to the use of silver nitrate. This is important as skull base bone erosion is the first confirmatory radiologic sign of its progression towards NOE.4Silver nitrate is commonly used in these patients and often imaging follows. This can lead to misinterpretation, potentially wrong diagnoses and hence more aggressive treatment.
CT is a quick and readily available imaging modality which can be used for diagnostic purposes in otology. Among its many uses in medicine; it is vital in differentiating otitis externa with its necrotizing counterpart. As both patients with OE and NOE frequently present with granulations which are cauterized with silver nitrate there is a risk the appearance of silver nitrate can be misinterpreted.
The radiopacity of silver nitrate can be attributed to its silver cation. As a metal its mass attenuation coefficient is described as high as 14 times that of cortical bone.3 This explains why only a thin layer over granulation tissues is mistaken for bone within the EAC as it is a narrow canal surrounded by bone. Further doubt is created in the context of NOE due to surrounding soft tissue swelling.
Our literature review revealed ten other cases in which silver nitrate artefacts were seen on imaging. However, only one of otologic origin was recently reported by Godse et al.6 They reported a case of a patient with EAC squamous cell carcinoma who presented with granulations which were biopsied and cauterized for haemostasis. A subsequent CT scan revealed a foreign body in EAC which was later attributed to be silver nitrate application.
Among other otolaryngology cases, Livingstone et al. reported silver nitrate artefact being misconstrued as a foreign body on CT imaging within pharyngeal mucosa after it was used for coagulation following incision and drainage for a peritonsillar abscess.7Likewise, Johnston et al. reported a case in which a patient underwent a revision bilateral Functional Endoscopic Sinus Surgery (FESS) after foreign bodies were noted in her paranasal sinuses by a CT of the sinuses.15 The foreign body was later identified as silver nitrate that had been used for recurrent epistaxis on a number of occasions in the ED.8
Further literature review highlighted a case in which wrongfully, a bony fragment in a supracondylar humeral fracture was reported on plain radiographs in the absence of clinical correlation.3Healy et al. reported two cases in which silver nitrate was incorrectly identified as a foreign body on plain radiographs of the fingers.9 A similar case was described by Peter Vu et al., in which the patient unfortunately underwent surgical intervention due to the artefactual appearance of fingertip heterotopic ossification.10