Improved diagnosis of a temporal lobe abscess in a post-irradiated nasopharyngeal carcinoma patient using diffusion-weighted magnetic resonance imaging

Bacterial brain abscess in patients with nasopharyngeal carcinoma following radiotherapy: microbiology, clinical features and therapeutic outcomes

Background

This study aimed to analyze the clinical features, causative pathogens, neuro-imaging findings, and therapeutic outcomes of bacterial brain abscess in patients with nasopharyngeal carcinoma (NPC) following radiotherapy.

Methods

NPC patients with bacterial brain abscess were evaluated. Their clinical data were collected over a 22-year period. For comparison, the clinical features, causative pathogens, neuro-imaging findings, and therapeutic outcomes between NPC and non-NPC patients were analyzed.

Results

NPC accounted for 5.7% (12/210) of the predisposing factors, with Viridans streptococci and Staphylococcus aureus as the two most common causative pathogens. Significant statistical analysis between the two groups (NPC and non-NPC patients) included chronic otitis media (COM) as the underlying disease, post-radiation necrosis by neuro-imaging, and the temporal lobe as the most common site of brain abscesses. The fatality rate in patients with and without NPC was 16.7% and 20.7%, respectively.

Conclusions

NPC patients with bacterial brain abscess frequently have COM as the underlying disease. Neuro-imaging often reveals both post-radiation necrosis and the temporal lobe as the most common site of brain abscesses, the diagnosis of which is not always a straightforward process. Radiation necrosis can mimic brain abscess on neuro-imaging and pose significant diagnostic challenges. Early diagnosis and treatment is essential for survival.

Delayed complications of radiotherapy treatment for nasopharyngeal carcinoma: imaging findings

Radiotherapy is used to treat a wide variety of head and neck tumours that arise in and around the skull base. The delayed effects of radiation damages a range of structures, including the nervous system, bone, major vessels, mucus membranes, pituitary and salivary glands, as well as increasing the risk of radiation-induced neoplasms. In this review the complications resulting from radiation treatment for nasopharyngeal carcinoma (NPC), a cancer treated with a high dose of radiation to a fairly large region, are illustrated. Many patients with NPC have a long-term survival, so are at risk of developing delayed radiation effects, and hence may demonstrate a wide range of complications on imaging. Other tumours around the skull base treated with radiotherapy include meningiomas, chordomas, chondrosarcomas, pituitary adenomas, paranasal sinus and nasal cavity tumours. In these cases similar complications may be encountered on imaging, although the severity, incidence and location will vary.

Diffusion-Weighted Magnetic Resonance Imaging in Radiation-Induced Cerebral Necrosis

OBJECTIVE

The objective of this retrospective study was to investigate the diffusivity of different components of radiation-induced cerebral necrosis with the hypothesis that the diffusivity of the various components is elevated to different degrees.

METHODS

Twenty-two patients (18 men, 4 women, aged 34-72 years) with radiation injury to the temporal lobes after radiation therapy (RT) for nasopharyngeal carcinoma with diagnosis confirmed on serial magnetic resonance imaging (MRI) were studied with coronal T2-weighted, diffusion-weighted, and gadolinium-enhanced MRI. Using three diffusion directions for diffusion-weighted MRI, the apparent diffusion coefficients (ADCs) of the enhanced component, the cystic or liquefied component, and the edema component were measured.

RESULTS

ADCs of all components of RT-induced cerebral necrosis (154 +/- 21.6 x 10(-5) mm2/s for contrast-enhanced component; 188 +/- 47.4 x 10(-5) mm2/s for cystic/liquefied component; 177 +/- 35.4 x 10(-5) mm2/s for edema component) were all significantly higher (P<0.00001) than ADC of the normal frontal lobe white matter (82 +/- 12.4 x 10(-5) mm2/s). The ADC of the enhanced component was significantly lower than that of the cystic/liquefied component (P=0.0096) and the edema component (P=0.003). A significantly lower ADC was shown in the enhanced component in temporal lobes showing both short-term morphologic deterioration (P=0.024) and occurrence of deterioration on long-term follow-up (P=0.04) compared with the temporal lobes that showed improvement or stable morphology.

CONCLUSIONS

ADCs of the contrast-enhanced component, cystic/liquefied component, and edema in RT-induced cerebral necrosis was significantly higher than in normal brain parenchyma. There is association between a lower ADC in the contrast-enhanced component and morphologic deterioration.