Abstract
Pancreatic carcinoma is an extremely high-grade malignant tumor with fast development and high mortality. The incidence of pancreatic carcinoma continues to increase. Peripancreatic invasion and metastasis are the main characteristics and important prognostic factors in pancreatic carcinoma, especially invasion into the nervous system; pancreatic nerve innervation includes the intrapancreatic and extrapancreatic nerves. A strong grasp of pancreatic nerve innervation may contribute to our understanding of pancreatic pain modalities and the metastatic routes for pancreatic carcinomas. Computed tomography (CT) and magnetic resonance imaging (MRI) are helpful techniques for depicting the anatomy of extrapancreatic nerve innervation. The purpose of the present work is to show and describe the anatomy of the extrapancreatic neural plexus and to elucidate its characteristics using CT and MRI, drawing on our own previous work and the research findings of others.
Keywords: Computed tomography, Magnetic resonance imaging, Extrapancreatic neural plexus
INTRODUCTION
Pancreatic carcinoma is a type of tumor associated with high mortality, and even in the early stages, peripancreatic invasion and metastasis are observed[1,2]. The pattern of cancer invasion via neural routes (perineural invasion) has been studied extensively, and 53% to 100% of results have reported neural invasion in pancreatic carcinoma. The perineural invasion and the degree of perineural invasion, especially of the extrapancreatic neural plexus, can provide some useful information for planning surgery, and it has also been shown to be an important prognostic factor for pancreatic carcinoma by several studies[3-16]. The innervation of the pancreas is a very important factor in the progression of disease, primarily of the biliary tract and pancreas and in surgical procedures[3,6,11,16]. It is critical for the anatomy of the extrapancreatic innervation of the pancreas to be made clear. Several studies have offered descriptions of the innervation of the pancreas[3,17,18].
The major celiac ganglia are distributed around the pancreas, and its nerve fiber branches not only mediated effective internal and external secretion in the pancreas but are also related to abdominal algesia. Neurotropic growth is one of the important biological features of pancreatic carcinoma[19,20]. Extrapancreatic neural plexus invasion was not only the prognostic indicator of pancreatic carcinoma but also related to the retroperitoneum recurrence after operation[21]. For the relief of intractable epigastric and back pain caused by advanced pancreatic carcinoma or other advanced epigastric tumors, computed tomography (CT)-guided celiac plexus block was widely launched in clinics[22-25]. Therefore, to understand the celiac ganglia that are invaded by epigastric malignancy, improving the likelihood of success for celiac plexus block, reducing complications, and correctly identifying celiac ganglia are essential.
The development of modern imaging technology has permitted imaging of the extrapancreatic neural plexus[12,26,27].
ANATOMY OF EXTRAPANCREATIC NERVE PLEXUS
Innervation of the pancreas by the sympathetic division of the autonomic nervous system occurs via the splanchnic nerves, and innervation by the parasympathetic division occurs via the vagus nerve[28]. Both types of nerves are generally accompanied by blood vessels. Both nerve divisions contribute efferent (motor) fibers to the walls of the blood vessels, the pancreatic ducts, and the pancreatic acini and visceral afferent (pain) fibers. For vagal afferent innervation, the major portion descends in the gastroduodenal branch toward the duodenum, pancreas, and pylorus[29].
The abundance of nerve fibers and their encasement of the neural plexus of pancreas, which consists of the intrapancreas nerve interlaced with the extrapancreatic, and the peripancreatic and retroperitoneal distribution of many netlike nerve fibers are the main reasons that pancreatic carcinoma easily causes nerve invasion and metastasis. The extrapancreatic neural plexus has six parts[30,31], including the following.
The neural plexus of the pancreatic head
Concerning the innervation of the pancreas, Yoshioka et al[32] and Yi et al[3] explained that the plexus pancreaticus capitalis (PLX) could be divided into two parts, PLX-I and -II. The main routes for both of the nerves from the celiac plexus and the ganglia to the pancreas include two parts, one being the direct route from the celiac ganglia to the posterior surface of the head of the pancreas (PLX-I) and the other route extending from the bilateral celiac ganglion to the left margin of the uncinate process, via the plexus, around the superior mesenteric artery (SMA) (PLX-II)[1] (Figures 1 and 2). Yi et al[3] also reported that the plexus from the celiac plexus to the pancreas head was divided into the anterior hepatic plexus and the posterior hepatic plexus; the former ran along the common hepatic artery, and the latter ran below and behind the portal venous system. The PLX-I represents approximately 20% of the fibers derived from the posterior hepatic plexus. The PLX-II is the portion most often invaded by pancreatic carcinoma, and it is reported to be involved in 74%-90% of cases of pancreatic head carcinoma[4,33].
The celiac plexus
The celiac plexus is the center of the viscus and composed of celiac ganglia, several large and small nerves that terminate with the celiac ganglia, several nerve fibers that originate from the ganglia, and the abdominal branch of the posterior vagal trunk. The celiac plexus is located in front of the superior segment of the abdominal aorta, surrounding the celiac trunk and the root of the SMA[34,35] (Figure 3). At dissection, most of the celiac ganglia were between thoracic 12 and lumbar 1 (T12 and L1), and these ganglia were found in the upper part of the retroperitoneum, in front of the diaphragmatic crura, medial to the adrenal glands, and near the aorta between the origin of the celiac artery and the SMA[26] (Figures 4 and 5).
The plexus around the superior mesenteric artery
There are many pancreatic branches from the SMA to the right edge of incisure of the pancreas, the center and to the right of the region behind the head of pancreas, which bypass the dorsal mesentery (Figure 6).
The hepatic plexus
This route and its branches go from the liver to the back and superior borders of the pancreatic head along the common hepatic artery and proper hepatic artery (Figure 7).
The aortic plexus
This route and its branches travel around the aorta and extend to the head and uncinate process of the pancreas (Figure 8A).
The splenic plexus
This route travels along the splenic artery, and the main route and its branches reach the tail of the pancreas (Figure 8B).
CT FINDINGS OF EXTRAPANCREATIC NERVE PLEXUS
Multi-detector row CT allows thinner images (1.0 or 0.5 mm) to be reconstructed, enabling clear identification of the details of the pancreatic and peripancreatic anatomies[36].
The neural plexus of the pancreatic head can be demonstrated clearly with CT imaging (Figures 9 and 10), showing a characteristic strand-like structure (Figure 10). Dal Pozzo et al[37] performed CT at the level of the celiac trunk and the SMA to identify the celiac ganglia. The celiac ganglia appeared as small lines, oval or laminar structures lower in density than the diaphragm; some were the same density as the diaphragm. In cadavers, the celiac ganglia on CT thus indicated corresponded exactly-by position, morphology, and dimensions-to the anatomic structures previously described in vivo (Figures 11 and 12). Rathmell et al[38] report the anatomy of the celiac plexus block using CT. We performed CT scanning on six cadavers and found that all of the left celiac ganglia were satisfactorily observed, whereas five out of six of the right celiac ganglia were satisfactorily shown. All of the celiac ganglia in the 6 cadavers were located between T12- L1, and their morphology was primarily laminar. The appearance of the celiac ganglia was high density (Figure 11). In addition, we also observed celiac ganglion in normal adults using CT. We found that both sides of the ganglia were of moderate density, the same as the liver and spleen or slightly lower than the diaphragma crura, in 650 cases (Figure 12).
MR FINDINGS OF EXTRAPANCREATIC NERVE PLEXUS
We studied the magnetic resonance imaging (MRI) findings of the celiac ganglia in cadavers and found that MRI can show the celiac ganglia accurately when the ganglia are large and labeled with gadolinium. These findings in cadavers can be a reference for identifying the celiac ganglia in vivo[26] (Figure 13).
On MRI in cadavers, all of the right and left ganglia were identified and found to be hyperintense relative to the liver and spleen (Figure 13). Seventy-five percent (75%) of celiac ganglia were located at the level between the celiac artery and the SMA, in front of the diaphragmatic crura and close and medial to the aorta. Twenty-five percent (25%) of celiac ganglia were at the level of the SMA. The celiac ganglion appeared lamina-shaped (85.38%), nodule-shaped (10%) and sickle-shaped (4.62%) (Figure 13). Both celiac ganglia were depicted at the same level on 83.33% of MRI images. Almost all celiac ganglia could be seen at the level of the pancreas. At the level of the head and body of the pancreas, the right (41.67%) and left (58.33%) celiac ganglia could be seen; at the level of the head of the pancreas, the right (25%) and left (16.67%) celiac ganglia could be seen; at the level of the body and tail of the pancreas, the right (33.33%) and the left (25%) celiac ganglia could be seen[26]. In healthy adults, the celiac ganglia characteristics were identical, in terms of position, morphology, and dimensions, to the anatomic structures previously described in cadavers. Most of the celiac ganglia were lamina- or line-shaped (Figures 13 and 14).
CONCLUSION
The anatomy of extrapancreatic neural plexus should be emphasized. The plexus includes six main parts, and the neural plexus of the pancreatic head is very important because it is easily invaded. These modern imaging techniques (CT and MRI) satisfactorily demonstrated the anatomy of the extrapancreatic nerve, which corresponded to the anatomy of the cadaver. The clear recognition and understanding of the innervation of the pancreas is necessary for surgical treatment of patients who have suffered nerve invasion by pancreatic carcinoma.
Footnotes
Supported by National Nature Science Foundation of China, No. 30370436
Peer reviewers: Aytekin Oto, MD, Associate Professor of Radiology, Chief of Abdominal Imaging and Body MRI, Department of Radiology, University of Chicago, 5841 S Maryland Ave, MC 2026 Chicago, IL 60637, United States; Weiguang Yao, PhD, Department of Medical Physics, Regional Cancer Program, Sudbury Regional Hospital, 41 Ramsey Lake Road, Sudbury, Ontario P3E 5J1, Canada; Dr. Charikleia Triantopoulou, Konstantopouleion Hospital, 3-5, Agias Olgas street, Athens 14233, Greece
S- Editor Cheng JX L- Editor A E- Editor Zheng XM
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