الفهرس 
Normal Anatomy of the neckOnly 14 pages are availabe for public view
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Abstract
A neck mass is a common finding and can present a difficult
diagnostic challenge. Neck masses can be divided into three main
categories: tumour and tumour like lesions, cystic and inflammatory
lesions. A variety of imaging techniques (like US, FNAUS, CT and
MR) can help in characterization of neck masses, but their
performance remains, however, unsatisfactory.
Diffusion-weighted imaging (DWI) is a noninvasive MRI technique
that provides image contrast dependent on the molecular motion of
water. Therefore, DWI provides in characterization of different tissues
and lesions.
The developments of echo-planar imaging (EPI), high gradient
amplitudes, multichannel coils, and parallel imaging have been
instrumental in extending the applications of DWI and increasing its
use for the evaluation of extracranial diseases. The extent of
translational diffusion of molecules measured in the human body is
referred to as the apparent diffusion coefficient (ADC). The ADC is
expected to vary according to the cellular density of the lesion.
Diffusion weighted imaging is successfully used in detection of
tumours. Tumours are frequently more cellular than the tissue from
which they originate, thus appear as high signal intensity (restricted
diffusion) at DWI. Metastases appear as high-signal-intensity foci at
DWI.
Summary and Conclusion Ch VIII
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The Diffusion weighted image can be used in differentiation between
benign and malignant lesions. The mean ADC value of benign solid
lesions is significantly higher than that of malignant tumors. The
differences in ADCs may reflect distinct differences in the
histopathologic features of the benign and malignant tumors.
Malignant tumours treatment modalities can produce edema, fibrous
inflammatory reaction, and scarring of the adjacent normal soft tissues.
On routine MR imaging, residual or recurrent lesions and treatmentinduced
changes show similar imaging characteristics and are,
therefore, difficult to distinguish.
By using the Diffusion weighted MRI, the mean ADC values for
residual or recurrent tumors are significantly lower than that for posttreatment
changes. Residual or recurrent lesions appeared as areas of
low signal intensity on the ADC map, while, post-treatment changes
appeared as areas of high signal intensity.
Also diffusion weighted imaging is helpeful for predicting treatment
response, as cellular tumor with low baseline pretreatment ADC values
respond better to chemotherapy or radiation treatment than tumors that
exhibit high pretreatment ADC values.
Diffusion-weighted MRI with ADC map can help the differentiation of
non-necrotic malignant from benign lymph node, delineation of the
solid viable part of the lymph node and even allows detecting small
adenopathies.
Summary and Conclusion Ch VIII
211
Metastatic and lymphomatous nodes appear hyperintense on DWI and
hypointense on ADC maps; adversely inflammatory nodes are
hypointense on DWI and hyperintense on ADC maps. The addition of
diffusion-weighted MRI to routine MRI provides additional useful
physiological and functional information regarding characterization of
the cervical lymph nodes.
The MRI criteria for metastatic lymph node include enlarged size of
minimal axial diameter of 8 to 9 mm in level II and 7 to 8 mm for the
rest of neck, shape tend to be spherical, extracapsular tumor spread and
abnormality of the internal architecture.
In Diffusion weighted imaging, the presence of necrotic areas greatly
affected the ADCs of metastatic nodes, resulting in large variability in
ADC values in the affected node.
All MRI criteria for nodal metastasis detection are helpful for
characterization of nodal metastasis. However, ADC values and
abnormal signal intensity on T1- and T2-weighted images are the most
reliable and significantly correlated to metastatic nodes.
The Diffusion weighted MRI can differentiate between nodal
Squamous cell carcinoma and lymphoma. The ADC values of
lymphoma were significantly lower than those of SCC.
DWI even differentiates between different grades of SCC. The ADC
values were significantly greater in the well and moderately
Summary and Conclusion Ch VIII
211
differentiated squamous cell carcinomas than in the poorly
differentiated squamous cell carcinomas.
Also DWI is useful in soft tissue tumours differentiation, in where the
ADC of myxoid tumours is significantly higher than that of nonmyxoid
tumors, because of the high mucin and low collagen contents
of mexoid tumours.
DWI also differentiates paraganglioma from other soft tissue tumours
of paraganglioma like criteria, in where the mean ADC of
paraganglioma is higher than the paraganglioma like tumours this
might be due to the vascular architecture of paraganglioma.
Diffusion weighted MRI with ADC map can be used in differentiation
between cystic and solid lesions, as the ADC value of cysts is generally
markedly higher than that of benign and malignant tumours. It can also
differentiate between different types of cysts and between cysts and
neoplastic or inflammatory necrotic lesions depend on its contents of
protein. The higher protein component in the fluid will increase the
viscosity and decrease the water proton mobility.
So the mean ADC of the benign cystic lesions is markedly higher than
both infammatory and tumoural necrosis and the ADC of the tumoral
necrotic lesions is markedly higher than that of infective necrotic
lesions (abscess and lymphadenitis), because in cystic or necrotic
tumors, the amount of the inflammatory cells and debris is much less
than the abscess cavity