RADIOLOGICAL ADVANCES IN ENT
Introduction: Advances in imaging have a great role in the field of Otorhinolaryngology. It leads to better understanding of the pathology with more specific diagnosis and thus better management.
The various imaging modalities includes:
1. Plain X-ray – There are so many imaging modalities, yet plain x-ray remains an excellent cost-effective low radiation imaging. It has limitations in soft tissue lesions and superimposition of various bony structures.
Indications:
- Radiopaque foreign bodies.
- Facial fractures.
- Sinusitis- shows opacification of sinuses
- Mastoiditis- shows opacification of mastoid air cells.
2. Computed tomography– This uses special x-ray equipment to obtain images from different angles. Images are then processed to show cross-section of body organs and tissues. It gives multi-dimensional planes like axial, coronal and sagittal planes. A more specialized type is High Resolution CT scan (HRCT) which gives images as thin as 0.6 to 1 mm cuts. HRCT with contrast is very useful in proper assessment of different pathological conditions. Indications for CT scan in ENT are as follows:
EAR
- Osteoma of external auditory canal.
- Keratosis obturans.
- Acute suppurative otitis media.
- Chronic otitis media.
- Cholesteatoma and complications.
- Ossicular discontinuity, Dehiscent facial nerve, High jugular bulb, Eroded tegmen & Lateral semicircular canal fistula.
- Petrous apex lesion.
- Meningoencephalic herniation.
- Glomus tumors, Jugular foramen tumors.
- Congenital anomalies of cochlea and ossicles.
- Otosclerosis- shows double cochlear sign with demineralization around cochlea (Otospongiosis).
- Fibrous dysplasia of otic capsule and temporal bone.
- Intracanalicular vestibular schwannomas.
NOSE
- Paranasal sinusitis.
- Sinonasal polyposis-to look for extent of disease, bony erosions and dangerous anatomical variations (for surgical planning).
- Paranasal sinus tumors.
- Inverted papilloma of nasal cavity.
- Lesions of skull base, pterygopalatine and infratemporal fossa.
THROAT
- Lesions of larynx, laryngopharynx, parapharyngeal and retropharyngeal spaces.
3. CT scan with 3 D reconstruction– It reconstructs 3 D images and provides information of the morphology that was not apparent in conventional CT scan.
Indications:
- Facial trauma- 3D CT scan show better delineation and extent of fracture with relation to surrounding structures.
- Paranasal sinuses and osteomeatal complex better delineated by 3 D reconstruction.
- Temporal bone 3 D reconstruction helps in better understanding of the anatomy of external, middle and inner ear.
- Head and neck tumors are better evaluated and helps in surgical planning for conservative procedures.
4. MRI is an imaging modality that produces cross-sectional images of human body in various planes without using ionization radiation. The images are obtained by exciting hydrogen protons of human body which then emit signals. The resultant images have an excellent tissue contrast which can differentiate between muscle, ligament, fat bone, fluid and pathological tissue in body. The unit of MRI is Tesla. Clinical MRI units usually operate at magnetic field strength of between 0.3 and 1.5 tesla. There are different sequences used for imaging in MRI. Commonly used sequences are T1 and T2.
Typical tissue appearance in MRI commonly in as follows:
Tissue | T1- weighted | T2- weighted |
CSF | Dark | Bright |
Fat (within bone marrow) | Bright | Light |
Inflammation | Dark | Bright |
Uses in ENT and head neck surgery:
- For evaluation of skull base, parapharyngeal and infratemporal lesions.
- Diffusion is a specialized form MRI sequence which helps to differentiate between Cholesteatomas and mucosal otitis media. Cholesteatoma appears bright in diffusion.
- High resolution T2 sequence known as CISS (Constructive Interference in Steady State) is used for evaluation of cochlear nerve, cochlea and looking for small intracanalicular acoustic neuromas.
- Contrast study is needed for detection of neoplasms, its extent of infiltration.
- Evaluation of mucoceles, encephaloceles and CSF rhinorrhea is done by MRI cisternography.
- MR Angiography is helpful for identifying vascular loops in hemifacial spasms and trigeminal neuralgia.
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