Replies to This Discussion

Permalink Reply by Dr.Muhammad Bashir Malik on June 9, 2011 at 3:37am

Dear Sir

One thing is very clear that ultrasound has advantage of non invasive as well as real time imaging modalities but few limitations especially for the extension of lesion and staging for malignant lesions however for vascular study and flow pattern Doppler ultrasound is of much value in all aspects like cost effective non invasive, easy availability but operator dependent.

warm regards   

Permalink Reply by Syed Amir Gilani on September 16, 2011 at 10:37am

Imaging Modalities

Potential imaging modalities include conventional radiographs, ultrasound (US), computed tomography (CT), magnetic resonance imaging (MRI) and nuclear medicine. Conventional radiographs are used for evaluation of patients with stridor, suspected retropharyngeal abscess or adenoid hypertrophy. Ultrasound is ideal for optimally determining whether a mass is cystic or solid, as well as for assessing whether a node is suppurative and for guiding abscess drainage. In addition, it is the imaging modality of choice in children with suspected thyroglossal duct cyst, not only to prove the cystic nature of the midline neck mass but also to confirm the presence of a normal- appearing bi-lobed thyroid gland in the lower neck.Ultrasound is also ideal for evaluating patients with suspected fibromatosis colli.Ultrasound, CT, or MRI can be used for evaluating jugular vein patency in patients with suspected Lemierre syndrome (internal jugular vein thrombophlebitis and septic emboli secondary to pharyngotonsillitis). CT and/ or MRI are frequently used to evaluate the total extent of more diffuse diseases, including inflammatory, congenital, and neoplastic processes. Since imaging with MRI frequently requires sedation in children less than 6 or 7 years of age, CT of the neck is more frequently performed on these children. CT of the neck is also frequently performed in combination with CT of the chest/abdomen/pelvis in children with neoplasms such as lymphoma. CT is ideal for evaluating osseous erosion in children with suspected rhabdomyosarcoma, with MRI frequently performed as an adjunct in patients with suspected intracranial or intraspinal extension. MRI is the preferred method of imaging in children with suspected hemangioma of infancy, congenital vascular malformations, cervical neuroblastoma, and neurofibroma. Nuclear medicine imaging is frequently used in combination with CT and/or MRI for evaluation of children with neuroblastoma (I-123), lymphoma (gallium-67 citrate or fluorodeoxyglucose positron emission tomography [FDG-PET]), osteomyelitis (technetium [Tc]-99m-methylene diphosphonate [MDP], gallium-67 citrate) and other neoplasms.

Permalink Reply by Syed Amir Gilani on September 16, 2011 at 10:39am

Choice of Imaging Modality:

CT is usually considered the basic initial study of the neck. It should be performed as a post-contrast examination with the patient supine and their head in a neutral position. Contrast is necessary to best differentiate pathological borders from normal tissue and to best separate adenopathy from vessels. Thus, CT examination should be ordered as a contrast study unless there is a medical reason not to give iodinated contrast. The scan should start above the skull base and extend caudally to at least the top of the manubrium. The scan should be performed as continuous 3 mm thick scans or as spiral scans with reconstructions at 2 mm. If skull base invasion is clinically suspected, a coronal scan of this area should be included as part of the initial examination.

One of the reasons CT is considered the basic imaging modality is because it has been shown that overall it evaluates lymphadenopathy better than MRI. That is, although MRI can also identify such disease, it is generally not as accurate as CT, it is more expensive than CT, and it takes longer both to perform the study and interpret the examination than CT. In the neck below the hard palate, CT is also generally considered the modality of choice due, in part, to its faster scan time than MRI and thus less degradation artefact due to swallowing and vascular pulsations.

In general, MRI is most often utilized as the primary imaging modality when evaluating tumor spread in the paranasal sinuses, cavernous sinuses, dura, brain, nasopharynx, oropharynx, palate, base of tongue, and floor of mouth. That is, the closer to the skull base, MRI offers more advantages over CT. MRI is also the modality of choice for evaluating perineural tumor spread. The MRI studies should include non-contrast and post contrast sequences. Although sequences can vary from one imaging center to another, most such studies should have at least T1-weighted, T2-weighted (spin echo or fast spin echo) and T1-weight post contrast fat suppressed series. Most of these sequences should be obtained in the axial and coronal projections. If applicable, sagittal images can also be obtained.

If one follows this imaging approach, there still will be cases that are initially imaged with one modality that then require a second study using the other imaging modality. Thus, if the initial examination is an MRI and there is skull base or facial bones invasion, CT often better shows the bone and often provides additional information helpful in surgical planning. Conversely, if CT is the initial study and retropharyngeal or perineural disease is suspected, MRI often adds complimentary information. This is also true for tongue base and floor of mouth cancers. In general, both examination are necessary on only about 10%-20% of cancer patients, however, in these cases, the surgeon can make the most informed treatment decisions possible.

It is best to discuss these difficult cases with the radiologist ahead of time to get the imaging input concerning the modality(s) of choice.

With the development of multidetector CT scanners, excellent reconstructions can be now be achieved in any plane with resolution indistinguishable from the that of the primary scan plane. In addition, with the more universal use of power contrast injectors, better perspicuity of pathology can be obtained. As a result, some of the advantage of MRI over CT may be diminishing in such areas such as the base of tongue, skull base, nasopharynx and parapharyngeal spaces.

Once a suspected deeply situated tumor mass is identified on a conventional CT or MRI study, CT guided biopsy should be considered. This technique is relatively painless to the patient and, if performed with a cytologist present, usually allows a tumor diagnosis to be confirmed. This approach often obviates the need for open surgical biopsy, especially in cases where curative surgery may not be feasible.

Ultrasound examination of superficial masses is recommended in children over CT or MRI. The ultrasound study of superficial lymph nodes can also distinguish metastatic nodes from reactive nodes by assessing nodal morphology and hilar vasculature, among other criteria. Ultrasound biopsy is also a valuable technique for masses in the thyroid gland and for primarily superficial masses. Deeply situated masses are probably more often biopsied by the CT guided technique.

The present generation of PET scanners have superior resolution to the prior units. In the untreated patient, a positive PET study allows identification of tumor, especially in difficult cases where no obvious mass was seen clinically or on either CT or MRI. However, the presence of inflammation in the post operative and/or post irradiated patient can also cause a positive PET study. As a result, PET is now often used in the difficult post treatment patient for its negative predicative value. Thus, a negative PET study has a very high correlation with the absence of tumor.