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Radiology in Head and Neck INTRODUCTION Radiology is a continually evolving medical specialty Since the discovery of xrays. Resulting in the numerous imaging modalities One should bear in mind that most imaging techniques utilizing ionizing radiation, including plain films, computed tomography (CT) and nuclear medicine Carry with them a lifetime risk of developing cancer.
Radiology in Head and Neck Presenter : Kanato T INTRODUCTION Radiology is a continually evolving medical specialty Since the discovery of x-rays Resulting in the numerous imaging modalities One should bear in mind that most imaging techniques utilizing ionizing radiation, including plain films, computed tomography (CT) and nuclear medicine Carry with them a lifetime risk of developing cancer Radiological Investigations Useful To The ENT Surgeon X-rays Ultrasound CT MRI PET Scans Barium Swallow Angiography Dacryocystography Sialography Orthopantomogram X-ray photons What Is an X-Ray? An x-ray is a discrete bundle of electromagnetic energy called a photon similar to other forms of electromagnetic energy such as light, infrared, ultraviolet, radio waves, or gamma rays Having no electrical charge, x-rays are more penetrating than other types of ionizing radiation (such as alpha or beta particles) and are therefore useful for imaging the human body Image Appearance Four basic densities: Air is black or very dark fat is generally gray and darker than muscle or blood Bone and calcium appear almost white Items that contain metal (such as prosthetic hips) and contrast agents also appear white The contrast agents are barium for gastrointestinal studies and iodine for most intravenously administered agents Image clarity Depends on kVp, mA, Time (sec) If radiograph is too light Increase kVp (increase the penetrating power or energy of the x-ray photons) Increase mA (produce more photons) Or to increase time (produce more x-ray photons) If a radiograph is too dark (overexposed) decrease kVp, mA, or time Conventional Radiology Temporal Bone: Law’s View, Schullars view, Stenver’s View, Transorbital View, Submentovertical View Nose and Paranasal Sinuses: Water’s View, Caldwell View, Lateral View, Right and Left Oblique Views, Lateral and Occlusal Views of Nasal Bone Neck: Lateral View and Anteroposterior Views of Neck, Soft Tissue Lateral View Nasopharynx, Submandibular Salivary Gland Law’s View (Lateral view of Mastoid) In 1913, Dr Frederik Law described lateral view of mastoid bone Sagittal plane of the skull is parallel to the flim X ray beam is projected 15 degree cephalocaudal Structures seen: External auditory canal (EAC) (superimposed on internal auditory canal (IAC)), mastoid air cells, tegmen, lateral sinus plate temporomandibula r joint Schullar’s view 1906, Dr Arthur Schuller, an Austrian neuroradiologist, described an oblique view of mastoid bone X-ray beam is projected 30° cephalocaudal and prevents superimposition of two sides of mastoid bones Structures seen: EAC superimposed on IAC, mastoid air cells, tegmen, lateral sinus plate, condyle of mandible, sinodural angle and atticoantral region (key areas for cholesteatoma and its erosion) DISADVANTAGES Long image acquisition time More chance of motion artifacts Difficult to stage both primary tumour and neck nodal disease Higher cost and less availability Absolute contraindications to MRI include patients with cardiac pacemakers, cochlear implants, and ferromagnetic intracranial aneurysm clips Those patients at risk for metallic orbital foreign bodies should be screened with plain films or CT before MRI Applications of MRI Tumors of nasopharynx, oropharynx, oral cavity and tongue „Extracapsular spread of tumor from nodes „Perineural spread and extension beyond gland of salivary gland tumors „Tumors of nose and paranasal sinuses: Distinguish between tumor and obstructed sinus secretions (hydrated fluid,viscous, desiccated); Perineural spread to anterior cranial fossa, orbit, parapharyngeal space and pterygopalatine fossa and cribriform plate extension „Lesions of IAC, facial nerve canal, and jugular foramen; acoustic schwannoma „Skull base tumors Radionuclide imaging Intravenously administered radiopharmaceuticals such as technetium-99m (99mTc)pertechnetate concentrate selectively in certain tissues and emit gamma radiation detected by a gamma camera It provides two-dimensional display of physiological and functional changes in tissue Technetium-99m (99mTc)pertechnetate scan: In salivary gland imaging 99mTc pertechnetate imaging may be useful for assessing salivary gland function in autoimmune and inflammatory disease of the salivary glands If obstructed, the degree of obstruction as well as the follow-up of obstruction after treatment can be assessed In evaluating neoplasms of the salivary glands the findings of the 99mTcpertechnetate scan are almost pathognomonic of Warthin's tumor and oncocytoma Thyroid imaging Most nuclear medicine imaging uses various isotopes of iodine (131I and 123I), Technitium-99m pertechnetate to determine thyroid function, identify hot or cold nodules, or access extent of thyroid masses and tumors 1- % of hot nodules – malignant Upto 25 % of cold nodule – malignant Positron emission tomography The positron emission tomography provide a means of identifying pathology based on altered tissue metabolism Imagining technique relies on a radioactive molecule(radiotracer) that decay with positron emission The radiotracer is given intravenously to the patient and is taken into cells Malignant cell trap more radiotracer compare to non malignant cells The local radiotracer concentration can be measured PET image lack anatomical details, which can be overcome by combining with CT/MR using software technique Depending on the radiotracer used different aspects of tissue metabolism can be measured An analogue of glucose, 2-[18F] fluoro-2deoxy-D-glucose (FDG) which reflects glucose metabolism is commonly use Positron Emission Tomography Used for staging and evaluation of recurrence for primary head and neck tumors, detecting distant lymph node, soft-tissue and skeletal metastases More accurate than CT or MRI in detecting residual or recurrent nodes Highly reliable after – months of end of treatment Indications of FDG with integrated PET/CT SCC patients with equivocal nodal disease following conventional assessment; -suspicion of recurrent/residual disease Patients with occult primary tumors Post-treatment papillary and follicular thyroid cancer patients with elevated thyroglobulin and negative 131-I scan Patients with clinical suspicion of more disease than conventional assessment demonstrates Patients where resectability is in doubt Effect of radiation The effects of radiation are usually classified into two categories, depending on the intensity of the radiation and the time period of exposure These electrons may damage DNA molecules directly or produce free radicals that can chemically damage genetic material; either effect may result in cell death or mutation These categories are referred to as stochastic effects deterministic effects Stochastic effects The severity of stochastic effects is independent of the absorbed dose Under certain exposure conditions, the effects may or may not occur There is no threshold and the probability of having the effects is proportional to the dose absorbed Example: radiation induced cancer, genetic effect Deterministic effects severity of certain effects on human beings will increase with increasing doses There exists a certain level, the "threshold", below which the effect will be absent This kind of effects is called "deterministic effects“ Example: cataract, erythema, infertility etc References Adam Grainger & Allison's Diagnostic Radiology 5th ed Basic Radiology LANGE clinical science Scott-Brown’s Otorhinolaryngology, Head and Neck Surgery 7th edition Surgery of ear Glasscock Shambaugh 6th edition Mohan Bansal Disease of Ear, Nose and Throat Head and Neck Imaging, Peter M Som Internet