Diffusion-weighted Magnetic Resonance Imaging as a Novel Imaging Modality in Assessing Treatment Response in Necrotizing Otitis Externa

The diagnostic conundrum in necrotizing otitis externa

Necrotizing otitis externa (NOE) is an aggressive and fast-evolving infection of the external auditory canal. Late diagnoses and untreated cases can lead to severe, even fatal consequences and so early diagnosis and treatment are paramount. NOE is a notoriously challenging diagnosis to make. It is therefore important to understand what diagnostic modalities are available and how otolaryngologists can use them to accurately treat such an aggressive disease. This review aims to evaluate the different diagnostic options available in NOE and discuss their advantages and limitations, thus, providing an up-to-date picture of the multimodal approach required in the diagnosis of this disease.

Advanced imaging of head and neck infections

When head and neck infection is suspected, appropriate imaging contributes to treatment decisions and prognosis. While contrast-enhanced CT is the standard imaging modality for evaluating head and neck infections, MRI can better characterize the skull base, intracranial involvement, and osteomyelitis, implying that these are complementary techniques for a comprehensive assessment. Both CT and MRI are useful in the evaluation of abscesses and thrombophlebitis, while MRI is especially useful in the evaluation of intracranial inflammatory spread/abscess formation, differentiation of abscess from other conditions, evaluation of the presence and activity of inflammation and osteomyelitis, evaluation of mastoid extension in middle ear cholesteatoma, and evaluation of facial neuritis and labyrinthitis. Apparent diffusion coefficient derived from diffusion-weighted imaging is useful for differential diagnosis and treatment response of head and neck infections in various anatomical sites. Dynamic contrast-enhanced MRI perfusion may be useful in assessing the activity of skull base osteomyelitis. MR bone imaging may be of additional value in evaluating bony structures of the skull base and jaw. Dual-energy CT is helpful in reducing metal artifacts, evaluating deep neck abscess, and detecting salivary stones. Subtraction CT techniques are used to detect progressive bone-destructive changes and to reduce dental amalgam artifacts. This article provides a region-based approach to the imaging evaluation of head and neck infections, using both conventional and advanced imaging techniques.

The Use of 99mTc-Mononuclear Leukocyte Scintigraphy for Necrotizing External Otitis Diagnosis

BACKGROUND

Necrotizing external otitis (NEO) is a severe infectious disease in the external acoustic meatus (EAM) and mastoid that may extend to the cranial base. Due to the lack of a gold standard examination technique, the diagnosis is often difficult and delayed. This study aimed to evaluate the sensitivity and specificity of ^99mTc-mononuclear leukocyte scintigraphy associated with ^99mTc-phytate in suspected NEO compared to ^99mTc-MDP and ⁶⁷Ga-citrate.

METHODS

A prospective study (32 patients) was conducted between 2011 and 2016.

RESULTS

At the end, twenty-four patients remained for the study conduction; nineteen had confirmed NEO diagnosis, one had sarcoma, one had EAM cholesteatoma, one had diffuse simple external otitis, and two had an inconclusive diagnosis. ^99mTc-mononuclear leukocyte scintigraphy plus ^99mTc-phytate was as sensitive as ^99mTc-MDP bone scintigraphy (19/19X9/19), and more sensitive than ⁶⁷Ga scintigraphy (19/19 x 17/19). Regarding specificity, it was superior to bone scintigraphy, 100% × 40% (5/5 × 2/5), and ⁶⁷Ga scintigraphy, 100% × 20% (5/5 × 1/5). After the infection resolution, all NEO patients had their leukocyte scintigraphy negativized. To the best of our knowledge, this is the first study that evaluates this technique in patients with suspected NEO.

CONCLUSIONS

^99mTc-mononuclear leukocyte was revealed to be the best option for NEO because of its specificity.

Diagnostic approach to patients at risk of otogenic skull base osteomyelitis

BACKGROUND

Otogenic skull base osteomyelitis (OSBO) is rare and potentially fatal sequelae of otitis externa. Accurate and timely diagnosis is important due to rising incidence, morbidity and costs associated with treatment. Consensus on the diagnostic approach for OSBO has yet to be reached, in particular the utility of imaging modalities.

AIMS/OBJECTIVES

This study reviews a single institution's high-volume experience of OSBO, with the aim of analysing clinicopathologic features and imaging studies to develop a diagnostic algorithm.

MATERIAL AND METHODS

A retrospective review of patients admitted with OSBO from 2009 to 2019, was performed. After applying inclusion and exclusion criteria, 103 patients with 106 unique episodes of suspected OSBO were selected. De-identified information including patient demographics, clinicopathologic features and imaging outcomes was recorded and analysed.

RESULTS

HbA1c ≥ 7% significantly predicted for OSBO in univariate (OR 7.83, 95% CI 1.85-33.16, p = 0.01) and multivariate analyses (OR 5.21, 95% CI 1.05-25.81, p = 0.04). The CT/technetium-99m/gallium-67 combination produced better diagnostic accuracy for OSBO (AUROC 0.96, 95% CI 0.92-1), when compared to a CT/MRI combination (AUROC 0.86, 95% CI 0.79-0.93).

CONCLUSIONS AND SIGNIFICANCE

Once there is a clinical suspicion for OSBO, diagnosis is established by synthesising results from clinical assessment, pathologic investigations and imaging modalities. The imaging utilised to diagnose OSBO should vary according to the clinical situation and limitations of each modality.

Necrotising Otitis Externa: A Review of Imaging Modalities

Necrotising Otitis Externa (NOE) has often posed some challenges in view of diagnosis and management by clinicians. One such challenge is the appropriate and timely use of imaging techniques since its use is critical not only in diagnosis but also in determining the extent and resolution of the disease. Hence, doctors in both primary and secondary health care need to be familiar with presenting symptoms while specialists need to be appraised of advances in imagining techniques in diagnosis and management of NOE. Whilst there is a general consensus amongst clinicians on some aspects of management of NOE, there is very limited consensus on the use of imaging modalities. There is no single modality of imaging that can provide a complete picture of diagnosis, disease progression and resolution. This review aims to highlight the strengths and weaknesses of various imaging techniques used in the diagnosis and management of NOE over the years and whether a multi-modal imaging technique at particular stages of the disease may provide better management outcomes.

Imaging of Acute and Chronic Skull Base Infection

Skull base infections are uncommon but can be life threatening without timely recognition. Imaging plays a crucial role because symptoms can be vague and nonlocalizing. Necrotizing otitis externa in diabetic or immunocompromised patients is the commonest cause of skull base osteomyelitis (SBO), followed by sinogenic infections and idiopathic central SBO. Multiparametric magnetic resonance (MR) and high-resolution CT are the mainstays for establishing a diagnosis and estimating disease extent, with MR being superior in ascertaining marrow and soft tissue involvement. Monitoring treatment response, of which imaging is a fundamental part, is challenging, with emerging promising imaging tools.

Current management of skull base osteomyelitis

PURPOSE OF REVIEW

Skull base osteomyelitis (SBO) is a life-threatening condition. Due to an aging and increasingly multimorbid population, clinicians are more often challenged with this disease. Yet, there is no consensus on the optimal diagnostic and follow-up management. This review should aid clinicians in decision-making for their patients.

RECENT FINDINGS

Treatment-resistant otalgia or headache is suspicious of SBO. Pseudomonas aeruginosa remains the most common pathogen but clinicians are challenged with increasing rates of sterile or fungal cultures due to previously applied antibiotics/steroids. No single imaging modality is able to detect the full extent of the disease. Whereas functional nuclear imaging with gallium-67 or methylene diphosphonate-technetium-99m was once advocated, its actual benefit is questionable. Newer modalities such as fluoro-D-glucose-positron emission tomography (PET)/computed tomography, PET/magnetic resonance imaging (MRI), or diffusion-weighted MRI seem to be promising in diagnosis and follow-up. Finding the causative pathogen is of utmost importance followed by long-term intravenous antibiotics until the disease has completely resolved. Surgery plays a minor role in treatment but can be helpful in selected cases.

SUMMARY

The numerous challenges in SBO render management difficult, but with a clear work-up including regular clinical, laboratory and imaging examinations, outcome can be improved.

Prediction of skull base osteomyelitis in necrotising otitis externa with diffusion-weighted imaging

OBJECTIVE

To predict skull base osteomyelitis in patients with necrotising otitis externa using diffusion-weighted imaging.

METHODS

A retrospective analysis was conducted of 25 necrotising otitis externa patients with skull base osteomyelitis (n = 10) or without skull base involvement (n = 14) who underwent a single-shot diffusion-weighted imaging of the skull base.

RESULTS

The respective mean apparent diffusion coefficient values of the skull base, as determined by two reviewers, were 0.851 ± 0.15 and 0.841 ± 0.14 ×10-3mm2/s for the skull base osteomyelitis patients, and 1.065 ± 0.19 and 1.045 ± 0.20 ×10-3mm2/s for the necrotising otitis externa patients without skull base involvement. The difference in apparent diffusion coefficients between the groups was significant, for both reviewers (p = 0.008 and 0.012). The optimal threshold apparent diffusion coefficient for predicting skull base osteomyelitis in necrotising otitis externa patients was 0.945 ×10-3mm2/s and 0.915 ×10-3mm2/s, with an area under the curve of 0.825 and 0.800, accuracy of 87.5 and 83.3 per cent, sensitivity of 85.7 and 90.0 per cent, and specificity of 90.0 and 78.6 per cent, for each reviewer respectively.

CONCLUSION

Apparent diffusion coefficient is a non-invasive imaging parameter useful for predicting skull base osteomyelitis in necrotising otitis externa patients.

Reliability of diffusion-weighted magnetic resonance imaging in differentiation of recurrent cholesteatoma and granulation tissue after intact canal wall mastoidectomy

Objective

To assess the reliability of diffusion-weighted magnetic resonance imaging in differentiating recurrent cholesteatoma from granulation tissue after intact canal wall mastoidectomy.

Methods

A prospective study was conducted of 56 consecutive patients with suspected cholesteatoma recurrence after intact canal wall mastoidectomy who underwent diffusion-weighted imaging and delayed contrast magnetic resonance imaging of the temporal bone. The final diagnosis was recurrence in 38 patients and granulation tissue in 18 patients.

Results

Cholesteatoma detection on diffusion-weighted imaging based on two sets of readings had sensitivity of 94.7 and 94.7 per cent, specificity of 94.4 and 88.9 per cent, and accuracy of 94.6 and 92.8 per cent, with good intra-observer agreement (Κ= 0.72,p= 0.001). Cholesteatoma detection on delayed contrast magnetic resonance imaging had sensitivity of 81.6 and 78.9 per cent, specificity of 77.8 and 66.7 per cent, and accuracy of 80.4 and 75.0 per cent, with fair intra-observer agreement (Κ= 0.57,p= 0.001). The mean cholesteatoma diameter on diffusion-weighted imaging was 7.7 ± 1.8 and 7.9 ± 1.8 mm, with excellent intra-observer agreement (Κ= 0.994,p= 0.001).

Conclusion

Diffusion-weighted imaging is a reliable method for differentiating recurrent cholesteatoma and granulation tissue after intact canal wall mastoidectomy.

Imaging in the Diagnosis and Management of Necrotizing Otitis Externa: A Survey of Practice Patterns

OBJECTIVE

To survey neurotologists and head and neck radiologists regarding use of imaging in the diagnosis and management of necrotizing otitis externa (NOE).

STUDY DESIGN

Cross-sectional survey study.

SETTING

Online survey distributed through email to specialty society membership lists.

PARTICIPANTS

Neurotologists and head and neck radiologists with membership in either the American Neurotology Society or The American Society of Head and Neck Radiology.

MAIN OUTCOME MEASURES

Responses to survey consisting of two demographic and seven clinically oriented questions related to the use of imaging in the diagnosis and management of NOE.

RESULTS

One hundred thirty-six participants responded to the survey. The imaging modality of choice in establishing the diagnosis of NOE selected by the respondents was computed tomography (CT) (37.5%) followed by technetium scintigraphy (21.3%). Magnetic resonance imaging (MRI) was the preferred investigation by 41.9% of participants for determining extent of disease. Gallium scanning was the imaging modality preferred by 32.4% of respondents for determining when to cease medical therapy. Ninety-five percent of participants responded that CT scans were always or frequently used in the diagnosis and management of NOE compared with 72.8% for MRI, 34.5% for gallium scans, and 34.2% for technetium scans.

CONCLUSIONS

There is considerable heterogeneity in the preferred imaging modalities used in the diagnosis and management of NOE. CT and MRI are the preferred contemporary modalities used by many physicians, demonstrating a shift away from the historic use of nuclear medicine scans.