The main reasons for performing FS examination are to evaluate the completeness of resection and also to check if ductal dilatation is active or passive, in order to avoid an excessive pancreatic resection.
In this paragraph, we will firstly discuss the value of FS according to the degree of dysplasia and the location of IPMN lesions in branch and/or main ducts. Then we will give the specificities according to the type of resection (i.e. PD, distal pancreatectomy, medial pancreatectomy, enucleation and total pancreatectomy).
These guidelines apply mainly to non invasive IPMN. Indeed, for IPMN with obvious malignant transformation, an hemi-pancreatectomy with lymphadenectomy is indicated, thus limiting discussion about the extent of pancreatic resection.
Guidelines to extend pancreatectomy: The standard option
There is no consensual agreement about the management of the residual pancreas according the pathological analysis of the pancreatic margin at FS. It well known that, in surgical series, the rate of invasive carcinoma in patients with IPMN involving the main duct is high, ranging from 45% to 57% vs
6% to 37% for branch-ducts IPMN[9
]. Furthermore, the risk of malignant transformation also greatly depends on the topography (i.e. branch ducts versus main duct) of the lesions: indeed, the 5-year risk of malignant transformation is 63% and 15% in main duct and branch ducts lesions respectively[16
]. As a matter of fact, branch-duct IPMN lesions are presently managed nonoperatively if asymptomatic and without morphological signs suggestive of malignant transformation[16
]. Then, according to the above data, in our center we analyze separately the lesions in main-duct and branch ducts[8
]. We treat even a minimal lesion involving the main duct by additional resection[8
]. Conversely, we tolerate residual mild dysplasia limited to branch ducts since it can be hypothesized that branch-duct IPMN-adenoma which is left in place carries a very delayed risk of recurrent evolutive disease[16
]. So, our standard option is to extend the pancreatectomy if FS reveals: (1) at least IPMN adenoma on the main duct; or (2) at least borderline IPMN on branch ducts; or (3) invasive carcinoma.
However, the decision to extend or not pancreatectomy does not exclusively depend on the FS result but also on age, general condition and presumed stage of the disease (malignant or benign). As a first example, the value of total pancreatectomy for invasive IPMN when the transection margin is involved by dysplasia is debated: some authors advocate extending pancreatectomy until a disease-free margin on the main pancreatic duct is obtained[22
] but most others, considering that long-term prognosis is affected mainly by the invasive component, do not recommend extending the pancreatectomy in this setting provided there is no invasive disease on the margin[10
]. As a second example, leaving IPMN adenoma in main duct may be acceptable in a high-risk patient while presence of high-grade dysplasia should in most cases lead to accept an additional resection.
Management of frozen sectioning according to the type of resection
Technical possibilities of extending the pancreatic resection greatly vary according to the different types of resection. Furthermore, consequences of pancreatic resections also vary between the different procedures and according to the size of the residual pancreas.
After PD, the risk of de novo
diabetes after PD is low, ranging from 0 to 7%[26
]. Some patients keep a normal endocrine function with a 5 to 6 cm pancreatic remnant limited to the tail. Lastly, since IPMN usually predominates in the right pancreas or is limited to this side[6
], it is possible in most cases to perform a complete resection.
According to these data, when the FS result on the pancreatic neck indicates to extend the resection, we recommend to remove a 2 to 3 cm additional pancreatic segment (progressively separated from the splenic vessels with ligature of their collaterals) and to check to the new transection margin by additional FS; if needed, a third or even fourth additional pancreatic resection can be performed (Figure ). The pancreatic tail can be preserved and anastomosed to the digestive track if its length is at least 5 to 6 cm to ensure a significant endocrine function[29
]. If the residual is less than 5 cm, three options are possible: (1) to try to perform an anastomosis which can be technically difficult with an uncertain long-term benefit; (2) to suture the margin and leave in place the remnant tail which can lead to a prolonged pancreatic fistula; and (3) to remove it, thus avoiding postoperative pancreatic complications but leading to a pancreatoprive diabetes. The former option can be chosen if the patient is young and there is no suspicion of residual disease.
Figure 5 Standard options to determine extent of pancreatectomy according to results of frozen sectioning of the pancreatic margin after pancreaticoduodenectomy and distal pancreatectomy. FS: Frozen sectioning; MD: Main duct; BD: Branch duct; CBD: Common bile (more ...)
It must be underlined that the attitude of successive resections with iterative FS during PD can limit the risk of surgically induced diabetes and, at the most, the risk of total pancreatectomy while suppressing all “risky” epithelium. As a matter of fact, in our previous series of 90 PD with FS, at least two margins (from 2 to 4) were examined by FS in 37% of procedures. Also, of the 127 patients in whom a partial pancreatectomy with FS was planned, only 9 (7%) ultimately underwent total pancreatectomy[8
In selected cases, a very short resection (limited to the tail) can be performed. In this case, it is easy to extend the resection if indicated by the FS result. In contrast, if the whole distal pancreas has been removed with division of the neck, the possibilities of extending the pancreatectomy are limited. The head-neck junction can be resected with division of the pancreas at the anterior edge of the common bile duct (or slightly on its left) provided the gastroduodenal artery has been mobilized with division of its pancreatic collaterals or even resected. This creates a wider transsection margin with a likely higher risk of fistula but with another possibility of FS (Figure ). If this latter margin is involved by IPMN lesions indicating an additional resection, this usually leads to complete the pancreatectomy by means of a PD provided the operative risk is low. Taking into account that IPMN lesions rarely predominate on the distal pancreas[6
], the risk of completing pancreatectomy during distal pancreatectomy is low but may exist. For this reason, the patient should be aware of this possibility.
The management of both margins analysis during medial pancreatectomy associates the analysis of each margin as performed for PD and DP[8
]. However, especially if there is some suspicion of segmental involvement of the main duct, FS results on both margins should be known before any additional resection is started. As an example, finding mild dysplasia on the main duct of the left margin should not indicate necessarily to extend resection to the left if high-grade dysplasia is present on the right-margin which should imply to resect the pancreatic head.
In this indication, FS is performed in order to: (1) to check, as for other procedures, if the resection is complete. For this purpose, the communicating duct is analyzed and is considered as a branch-duct with a cut-off tolerating only mild dysplasia as described above. Since the communicating dust is usually small in diameter (less than 1 mm), the surgeon must mark it with a stitch or give it separately; and (2) to exclude invasive malignancy which requires an oncological resection[31
]. For this purpose, the cyst is opened by the pathologist who select a suspect area if present i.e. papillae, mural nodule or wall thickening. Since there is no strict correlation between gross aspect and histology in case of microinfiltrative adenocarcinoma, we recommend to routinely perform this analysis. Moreover, the histological grading of dysplasia in the cyst can help to analyze the communicating duct which is always limited in size.
Total pancreatectomy: In some patients, a total pancreatectomy is planned. However, it can be interesting to perform it as a two-step procedure event if it is more complicated. Indeed, passive dilatation associated with IPMN can mimic diffuse main duct involvement. Passive dilatation can be located upstream from a stenosis (usually due to invasive carcinoma) but also downstream from a mucin-producing lesion resulting in ductal dilatation towards the papilla.