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Type:
Educational Exhibit
Keywords:
Tissue characterisation, Neoplasia, Experimental investigations, Diagnostic procedure, Ultrasound, Experimental, Elastography, Ultrasound physics, Pancreas, Abdomen
Authors:
S. Crosara, M. D'Onofrio, R. De Robertis, S. Canestrini, E. Demozzi, R. Pozzi Mucelli; Verona/IT
DOI:
10.1594/ecr2014/C-0686
Findings and procedure details
SOLID LESIONS
As well known,
pancreatic ductal adenocarcinoma is a firm mass,
stiffer than the adjacent parenchyma [10],
owing to the presence of fibrosis and marked desmoplasia,
and therefore it is characterized by a higher wave velocity value (Fig.
4 and Fig.
5).
A wide range of values results also from our personal experience and only few data have been reported in the literature.
Our latest unpublished data identify a velocity cut-off value (4 m/s) with 100% specificity and 100% positive predictive value (Tab) in diagnosing pancreatic ductal adenocarcinoma.
Pancreatic stiffness measured by ARFI is reported to be high also in patients with chronic pancreatitis [11],
thus making a differential diagnosis difficult.
ARFI can also be applied in the detection of pancreatic lesions (Fig.
6),
improving their conspicuity thanks to the stiffness difference between the lesion itself and the pancreatic gland.
CYSTIC LESIONS
ARFI has not been tested only in solid tissues evaluation [6,12-14].
Although mechanical waves (US) propagates through solids and shear waves are highly attenuated in fluids in which only longitudinal waves or shear wave reflection at the solid-fluid interface may be measured,
the wide range of differences of fluids in vivo led to test ARFI also on fluids and different responses have been obtained according to their viscosity and the presence of suspended particles [15-18].
In the daily clinical practice,
cystic masses are still characterized and classified at imaging on the basis of their morphology,
architecture and vascularization (parietal thickness,
the presence and vascularity of septa and parietal nodules,
the presence of calcifications and communication with the main pancreatic duct) [17].
Nevertheless,
the definitive diagnosis of pancreatic cystic lesions sometimes still requires an invasive analysis of the cystic content.
Morover,
fluids in vivo can be really different.
The test of ARFI on fluids provided different responses according to viscosity: serous cystadenoma is characterized by simple fluid content (in wich the propagation speed of shear wave is always represented by the non-numerical value “XXXX/0”) [16],
whereas mucinous cystic lesions have high viscous and particle fluid content (in complex fluids,
more viscous than water,
numerical values are obtained) [16,18].
In accordance with pathologic descriptions of fluids contained in different pancreatic cystic lesions,
their complex nature could be determined by the presence of mucin,
as in mucinous cystic neoplasms (Fig.
7) and mucinous intraductal papillary tumors (Fig.
8),
or as result of intralesional bleeding or necrosis,
as may occur in pseudocyst.
To distinguish mucinous cystic lesions (potentially malignant) from serous cystic lesions (mainly benign) and to confirm the datain the literature [17],
the result “XXXX/0” was considered indicative of simple liquids (comparable to water) (Fig.
9).
To identify lesions containing complex fluids,
and therefore potentially mucinous,
two different methods of reading can be used in our experience [19]:
1.
At least two numerical values obtained when performing 5 measurements;
2.
The prevalence of numerical values obtained irrespective of the number of measurements.
On the basis of the results obtained in our experience [19],
ARFI imaging with Virtual Touch Tissue Quantification could be of additional value in the characterization of pancreatic cystic lesions by noninvasive fluid evaluation.
The good sensitivity (68.8%) of the first reading method (at least 2 numerical values obtained when performing 5 measurements) and the excellent specificity (100%) of the second method (prevalence of numerical measurements) for the diagnosis of mucinous cystic neoplasms and intraductal papillary mucinous neoplasms (unpublished data) with Virtual Touch Tissue Quantification show how this technique could represent an important medium for characterization of mucinous pancreatic cystic lesions (potentially malignant) as well as diagnostic and therapeutic management.
In particular,
the first method of diagnosis can be used to exclude malignancy or to identify those patients eligible for follow-up.
Because of its high specificity,
the second method,
can be used to confirm malignancy in those patients who are candidates for surgical resection.