Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_1441_Библиотеки_им_академика_М_И_Перельмана.pdf
296 Mesenteric component of exure mobilization
Separation of the colon from underlying fascia continues
along the descending colon toward the colic component
of the exure. Colofascial separation here completes colic
detachment (Figure 20.1d).
To achieve colofascial separation, the colon may be
peeled or stripped off the underlying fascia. is is asso-
ciated with some bleeding that stops with packing and
tamponade. Alternatively, the interface between colon
and fascia may be diathermy separated or sharply sepa-
rated using dissecting scissors. Once the colic component
is fully mobilized, it can be medialized to demonstrate the
mesofascial interface.
Mesenteric component
e mesenteric component of the exure (i.e., the splenic
mesenteric conuence) is best conceptualized in terms of
longitudinal and radial axes. e longitudinal axis occurs
from the transverse to left mesocolon (or vice versa). e
radial axis extends from the nonintestinal (attached) zone to
the intestinal (nonattached) zone of mesentery (Figure 20.1e).
As described earlier, the transverse mesocolon is par-
tially mobilized once the greater omentum and spleno-
colic reection have been separated from it. ese activities
address the longitudinal axis of the exure. Continuing the
process of left mesofascial separation as far medially and
cephalad as possible fully separates or detaches the mesoco-
lon across its radial axis (i.e., from attached to nonattached
zones). Aswith colofascial separation, mesofascial separa-
tion can be conducted either by stripping the mesentery o
the retroperitoneum or diathermy division at the mesofas-
cial interface. Mesofascial separation has been completed
when the middle colic adipovascular pedicle is encountered
and further mobilization impeded by this.
At this stage, the mesenteric, colic, and peritoneal com-
ponents of the exure have been fully mobilized.
HEPATIC FLEXURE
e principles of hepatic exural mobilization are identical
to those of splenic exure mobilization and likewise can be
detailed in terms of anatomic components.
Peritoneal component
Mobilization of the hepatic exure will be described in
terms of its peritoneal, colic, and mesenteric components
(Figure 20.2a and b). When the right colon is retracted medi-
ally, traction is transmitted to the right peritoneal reec-
tion, which can then be divided sharply (i.e., peritonotomy)
(Figure 20.2c). e index nger of the left hand can be placed
beneath the right peritoneal reection and directed toward
the hepatic exure. e peritonotomy is then extended
onto the nger as far as the hepatocolic peritoneal reec-
tion (Figure 20.2c). Some surgeons use hemostatic sealant
devices to divide the hepatocolic peritoneal reection, while
others advocate sharp division and tamponade by packing.
In general, the greater omentum does not extend to over-
lie the hepatocolic refl ction but it can do in patients with
considerable visceral adiposity. In these patients, the omen-
tum fuses with the hepatocolic peritoneal refl ction. In this
context, the omentum should fi st be separated from the
transverse colon medially (see splenic flexu e).
As with the splenic exure, peritonotomy permits access
to the colofascial interface. Following completion of the
peritonotomy of the right peritoneal and hepatocolic peri-
toneal reection, the hepatic exure remains attached by its
colic and mesenteric components.
Colic component
When the right colon is retracted medially the colofascial
interface comes under tension, and the interface between
colon and fascia is exaggerated (Figure 20.2d). e right
colon can be peeled from the fascia by gentle traction with
countertraction on the fascia. Alternatively, the fascial
interface can be diathermy divided. is process is then
continued proximally up to the colic component of the
hepatic exure. e hepatic exure now remains attached
at the mesentery.
Mesenteric component of the hepatic
exure
As with the splenic exure, the hepatic mesenteric compo-
nent is best considered in terms of its longitudinal (i.e., the
conuence between right and transverse mesocolon) and
radial axis (spanning from the attached mesentery to non-
adherent intestinal margin) (Figure 20.2e). Mobilization
along the longitudinal axis involves extending right meso-
colonic mobilization as far cephalad and medial as pos-
sible. Care is taken during the medial component, where
the second and third parts of the duodenum (and head
of the pancreas) are encountered. With these maneuvers,
the mesenteric conuence at the hepatic exure is fully
detached along both longitudinal and radial axes. Further
mobilization is limited by the middle colic adipovascular
pedicle. By now, however, one will notice that the hepatic
exure is fully mobile and the right colon can be fully
medialized.
ILEOCOLIC MESENTERIC FLEXURE
e central principles are based on peritoneal, intestinal,
and mesenteric continuity and are identical to those for
splenic and hepatic exure mobilization (Figure 20.3a).
Peritoneal component
e rst step is to divide (i.e., peritonotomy) the ileoce-
cal peritoneal reection at the inferior aspect of the ileoce-
caljunction (Figure 20.3b). is reection is an extension
of the peritoneal reection at the base of the small intestinal
Ileocolic mesenteric exure 297
Hepatic flexure
(e)
Peritoneal
component
Fascial
component
Mesenteric
component
(c) (d)
(a)
(b)
Colic
component
Fascial
component
Mesenteric
component
Peritoneal
componen
t
Right peritoneal
reflection
Intact
Mesenteric
component
Figure 20.2 (see also QR 11 and 12) (a) 2.5D image derived from a 3D digital model of the hepatic exure. (b) The exure
(including all components) has been slightly displaced from adjacent structures to demonstrate continuity of each and
contiguity between each. (c)Sectionthrough the exure demonstrating the right peritoneal reection and its relationship
to underlying colic andmesenteric exural components. (d) Section through the ascending colon (after peritonotomy) it
has been separated from the underlying fascia (i.e., colofascial separation). (e) Demonstration of mesenteric component of
hepatic exure in terms oflongitudinal and radial axes.
298 Mesenteric component of exure mobilization
mesentery (i.e., where the latter curves onto the posterior
abdominal wall and becomes adherent). Peritonotomy
of the ileocecal peritoneal reection is continued later-
ally onto the right peritoneal reection (Figure 20.2b)
and medially onto the small bowel mesenteric reection
(Figure20.3c).
Colic and mesenteric components
Once the peritoneal refl ction has been divided, only the
colo- and mesofascial interface remain attached. As ear-
lier, the flexu e is best thought of in terms of radial and
longitudinal axes. e former extends from attached to
nonattached intestinal mesenteric margin. e latter
includes the continuity between the small intestinal and
right mesocolon. Th s continuity has an apex at the ileoce-
cal junction.
Given that the ileocecal junction is generally mobile,
there is a short or limited colofascial plane in this region.
In cases where the intestinal component is attached, then
a colofascial interface will be encountered and the compo-
nents are separated (Figure 20.3). e intestinal component
of the ileocecal junction is lied anteriorly, away from the
retroperitoneum, which places the latter under stretch and
transmits traction to the interface. is exaggerates the
interface and the components may be separated either by
peeling the mesentery off the fascia or by dividing through
the fascia.
At the right colon, colo- and then mesofascial sepa-
ration is completed. At the small bowel mesentery, fur-
ther mesofascial separation mobilizes the mesentery o
the retroperitoneum and the inferior vena cava comes
intoview. By now, however, the entire ileocecal exure will
have been fully detached from the fascia and underlying
retroperitoneum.
DUODENAL AND SIGMOIDAL FLEXURES
e principles of mobilization or detachment of the ex-
ures are similar for all exures. e peritoneal component
is divided, which permits access to the mesenteric-fascial or
mesosigmoid-fascial plane. Mesenteric-fascial separation
above, below, and at the exure leads to mobilization along
both longitudinal and radial axes and completes exural
detachment.
FUTURE DIRECTIONS
e exures have traditionally been viewed as challeng-
ing from a technical standpoint. e above descriptions
provide a roadmap along which exural mobilization or
detachment may be conducted in a universally reproduc-
ible manner. As with other aspects of colorectal surgery, this
provides an anatomic basis for the international standard-
ization of exural mobilization.
SUMMARY
e exures can be understood as comprising four continu-
ous and contiguous structures. Two of these, the peritoneum
and colon, are centered on a mesenteric conuence. In con-
ceptualizing exures in these terms, exural detachment
and resection are greatly simplifi d and thus reproduced.
Ileocecal peritoneal re˜ec tion
(a)
(b)
Fascial
component
Mesenteric
component
Peritoneal
component
Peritoneal
component
Peritoneal
component
Intact
Figure 20.3 (a) 2.5D image derived from a 3D digital model of the ileocecal exure. (b) The exure (including all components)
has been slightly displaced from adjacent structures to demonstrate continuity of each and contiguity between each.
References 299
REFERENCES
1. Treves, F., Lectures on the anatomy of the intestinal
canal and peritoneum in man. Br Med J, 1885.
1(1264): 580–583.
2. Sehgal, R. and J.C. Coffey, Historical development of
mesenteric anatomy provides a universally applica-
ble anatomic paradigm for complete/total mesocolic
excision. Gastroenterol Rep, 2014. 2(4): 245 –250.
3. Culligan, K. etal., The mesocolon: A prospective
observational study. Colorectal Dis, 2012. 14(4):
421–428; discussion 428–430.
4. Culligan, K. etal., The mesocolon: A histological
and electron microscopic characterization of the
mesenteric attachment of the colon prior to and
after surgical mobilization. Ann Surg, 2014. 260(6):
1048–1056.
5. Coffey, J.C., Surgical anatomy and anatomic
surgery—Clinical and scientic mutualism. Surgeon,
2013. 11(4): 177–182.
6. Coffey, J.C. etal., Terminology and nomencla-
ture incolonic surgery: Universal application of
a rule-based approach derived from updates on
mesenteric anatomy. Tech Coloproctol, 2014.
18(9):789–794.
7. Coffey, J.C. etal., Mesenteric-based surgery exploits
gastrointestinal, peritoneal, mesenteric and fascial
continuity from duodenojejunal exure to the
anorectal junction—A review. Dig Surg, 2015. 32(4):
291–300.
8. Ellis, H. and V. Mahadevan, Clinical Anatomy:
Applied Anatomy for Students and Junior Doctors.
Wiley, Chichester, U.K., 2013, pp. 85–89.
9. Netter, F.H., Atlas of Human Anatomy. Elsevier
Health Sciences, Philadelphia, PA, 2014,
pp.263–268, 269–276.
10. Sinnatamby, C.S., Last’s Anatomy: Regional and
Applied. Elsevier Health Sciences, New York, 2011,
pp. 234–238, 247–259.
11. Standring, S., Gray’s Anatomy: The Anatomical Basis
of Clinical Practice. Elsevier Health Sciences, U.K.,
2015, pp. 1085, 1143
12. Coffey, J.C. etal., An appraisal of the computed
axial tomographic appearance of the human
mesentery based on mesenteric contiguity from
theduodenojejunal exure to the mesorectal level.
Eur Radiol, 2016. 26(3): 714 –721.
13. Peirce, C. etal., Digital sculpting in surgery: A novel
approach to depicting mesosigmoid mobilization.
Tech Coloproctol, 2014. 18(7): 653–660.
301
21
Mesenteric considerations in resection
ofthetransverse colon
J. CALVIN COFFEY AND IAN LAVERY
Science is organised knowledge. Wisdom is
organised life.
Immanuel Kant
AIM
To demonstrate the mesenteric and peritoneal basis of
mobilization of the transverse mesocolon.
INTRODUCTION
Classical anatomic depictions of the transverse mesocolon
describe it as inserting directly into the posterior abdominal
wall along a linear attachment [1–7]. As per these descrip-
tions, the line of attachment extends from the hepatic exure
across the upper abdomen to the splenic exure. According
to the current appraisal of mesenteric anatomy, the trans-
verse mesocolon is formed by a coalescence of both hepato-
colic and splenocolic mesenteric conuence, at the middle
colic adipovascular pedicle [1,2,7–10]. As such the transverse
mesocolon does not have a linear attachment to the poste-
rior abdominal wall per se. Instead, it is mainly comprised
of mesenteric regions attached over a broad area. From this
zone of mesofascial adhesion, the mesocolon extends to the
transverse colon itself. At the intestinal boundary, it elongates
considerably in tandem with the transverse colon.
e greater omentum is draped over the transverse meso-
colon and focally adherent at several points. Furthermore,
a peritoneal refl ction occurs between the under surface of
the greater omentum and the upper margin of the transverse
colon and although an anatomic constant, it has yet to be
named. If one considers the transverse mesocolon in the
context of these anatomic arrangements, then its mobiliza-
tion and division become a straightforward technical matter
that can be readily conducted in a reproducible manner.
LAPAROSCOPIC/ROBOTIC MOBILIZATION
AND DIVISION OF THE TRANSVERSE
MESOCOLON
Laparoscopic/robotic mobilization
ofthegreateromentum
In general, transverse mesocolic mobilization is conducted
either as part of an extended right or left mesocolectomy,
or total mesocolic excision. As the latter is more common,
this will be used as the platform to describe steps in its
Aim 301
Introduction 301
Laparoscopic/robotic mobilization and division of the
transverse colon 301
Laparoscopic/robotic mobilization of the greater
omentum 301
Laparoscopic/robotic mobilization of the splenic exure 302
Laparoscopic/robotic mobilization of the transverse
mesocolon 303
Identication of the mesenteric margin 303
Laparoscopic/robotic division of the middle colic
adipovascular pedicle 303
Open transverse mesocolic mobilization and division 305
Mobilizing the greater omentum from the
transversemesocolon 305
Mobilization from the left 305
Mobilization from the right 305
The mesenteric root region 305
Future directions 309
Summary 309
References 309
302 Mesenteric considerations in resection ofthetransverse colon
mobilization. In total mesocolectomy, the left and right sides
are fi st mobilized by some authors, while others commence
on the left and progress proximally around the transverse
mesocolon toward the right side.
As a fi st step, many mobilize the greater omentum o
the transverse mesocolon, thereby gaining access into the
lesser sac. To do this, an assistant holds up the greater
omentum with the patient in the head up position while
the surgeon places countertraction on the greater omen-
tum (Figure 21.1). e greater omentum is divided in a
hemostatic manner. e division commences distal to the
gastroepiploic arcade so as not to compromise the lat-
ter. Ingeneral, in this region, the greater omentum is not
attached to the underlying mesocolon, which means that
omentotomy here accesses the lesser sac proper. Once
opened in this region, the omental division is continued le
and laterally to the junction between right and left gastro-
epiploic vessels. Atthe lateral extreme of the lesser sac, the
omentum is adherent to underlying transverse mesocolon.
Adhesions here must be divided to fully expose the underly-
ing mesocolon (Figure 21.2) [11–13].
Laparoscopic/robotic mobilization
ofthesplenicexure
At the flexu e proper, the omentum and splenocolic refl c-
tion coalesce to a variable degree and oen it is not possible
to dierentiate either. Continued division of the omentum/
refl ction here will bring the surgeon around to the le
peritoneal refl ction. In general at this stage, and in par-
ticular if one retracts the splenic component of the flexu e
to the right iliac fossa, a mesofascial interface is identiable.
Th s is the interface between the splenic mesenteric conu-
ence and Toldt’s fascia (Figure 21.3).
Left (Toldt’s )
mesocolic fascia
Toldt’s fascia between
mesocolon and
retroperitoneum
Mesenteric componen
t
of splenic flexure
Splenic flexure
Coalescence of greater
omentum and
splenocolic reflection
Figure 21.3 (See also QR 2/5.) Robotic view of mesofascial
interface formed between the mesenteric component of
the splenic exure and underlying Toldt’s fascia. When the
transverse mesocolon is retracted toward the right iliac
fossa the fascia is placed under stretch and the interface
formed between it and the mesocolon becomes apparent.
Transverse
mesocolon
Omentomesocolic
adhesions
Omentomesocolic adhesions
Greater
omentum
Figure 21.2 Laparoscopic view of omentomesocolic
adhesions that are divided in order to fully separate the
omentum from the mesocolon. This activity is essential as
it later permits the surgeon fully isolate the middle colic
adipovascular pedicle.
Transverse mesocolon
upper surface
Lesser sac
Entering lesser sac
Greater omentum
Figure 21.1 (See also QR 2d/10.) Laparoscopic view of the
greater omentumand the manner in which it is grasped
to enabledivision. Lateral to the gastroepiploic arcade
the omentum is not attached to the upper surface of the
transverse mesocolon. As a result, its division provides the
surgeon with direct and unimpeded access to the lesser sac.
Laparoscopic/robotic mobilization and division of the transverse mesocolon 303
Laparoscopic/robotic mobilization
ofthetransverse mesocolon
Before describing mobilization of the transverse mesocolon,
it is important to describe the anatomy of the operative fi ld
(see Chapter 20 for details). e left mesocolon and colon
will have been mobilized. e left peritoneal and splenocolic
reection will have been divided, and the greater omentum
freed from the upper surface of the transverse mesocolon.
Finally, a mesenteric margin will have been created follow-
ing division of the inferior mesenteric artery and vein, as
well as intervening mesentery (Figure 21.4). e divided
edge of the mesentery is a crucially important landmark
and provides the starting point for transverse mesocolic
mobilization and division [11–13].
Identication of the mesenteric margin
e patient is placed in a slight head up position. e greater
omentum attached to the stomach is deected up under the
left hemidiaphragm. e left colon (just distal to the splenic
exure) is lied toward the anterior abdominal wall and to
the le. e transverse colon (just proximal to the splenic
exure) is lied toward the anterior abdominal wall and to
the right. e tension created is transmitted to the mesoco-
lon that is “opened out” (Figure 21.5). ese activities expose
the divided margin of the mesocolon (Figure 21.6). e
mesocolon can be directly divided at this point because the
greater omentum has been dissected off the upper surface of
the transverse mesocolon (see earlier). Mesocolic division
using a tissue sealant device is continued until the middle
colic adipovascular pedicle is reached near the midline.
Laparoscopic/robotic division of the
middlecolic adipovascular pedicle
e middle colic vessel originates from the superior mes-
enteric artery at the mesenteric root region (Figure 21.7).
is relationship is important to bear in mind. If dissection
Left mesocolon
Transverse mesocolon
Mesenteric margin
Figure 21.4 (See also QR 1/6 and 7.) The mesenteric mar-
gin. This is created as a result of peritonotomy of the peri-
toneal reection at the right side of the mesosigmoid and
division of the inferior mesenteric adipovascular pedicle. It
is important to identify as it provides the starting point for
mesenterotomy of the transverse mesocolon and isolation
of the middle colic pedicle.
Lesser
sac
To mesenteric
root region
Middle colic
adipovascular pedicle
Transverse
mesocolon
Middle colic adipovascular pedicle
Undersurface of
transverse mesocolon
Figure 21.5 Laparoscopic view of the transverse
mesocolon that has been spread and thereby “opened
up,” to expose the middle colic vascular pedicle.
Thisactivity is crucial in identifying the transverse
mesocolon and permitting its division.
Transverse
mesocolon
Lesser sac
Mesenteric
root region
Origin of middle colic
from mesenteric
root region
Mesenteric root region
Figure 21.6 (See also QR 1/8.) Laparoscopic view differen-
tiating avascular mesenteric regions on either side of the
middle colic adipovascular pedicle.
304 Mesenteric considerations in resection ofthetransverse colon
of the middle colic is too low, then the superior mesenteric
artery could be compromised. To avoid this, the middle
colic is best divided high up along its mesenteric pedicle.
e approach is based on the presence of avascular mes-
enteric regions occurring on either side of the middle colic
vascular pedicle (Figure 21.8).
e avascular mesentery, on either side of the pedicle,
is divided using a tissue sealant device such as the har-
monic scalpel. is isolates the pedicle for further dissec-
tion. e fat of the pedicle is slowly dissected through in
a stepwise and gradual manner under high magnication.
Given that the greater omentum was already freed from the
upper surface of the mesocolon, the middle colic vessel can
be skeletonized circumferentially. Once exposed, it can be
securely clipped (or stapled) and divided (Figure21.9).
Where there is an artery there is a vein and so care
must be taken to identify this and manage it using the
same approach (Figure 21.9). At the right side of the
middle colic adipovascular pedicle, a further interpe-
dicular mesocolic region occurs between the right (pres-
ent in 25%) and middle colic vessels. This again can be
directly divided as the greater omentum was separated
off the transverse mesocolon as described earlier. This
completes laparoscopic transverse mesocolic mobiliza-
tion [11–13] .
Transverse mesocolo
n
Middle colic vessel
Skeletonization of middle colic vessel
Lesser sac
Figure 21.8 Laparoscopic isolation of the middle colic
pedicle by dividing avascular mesocolic regions on
eitherside.
T
ransverse mesocolon
Transverse mesocolon
Middle colic vein
Middle colic artery
Lesser sac
Clipping and division of middle colic vessels
Figure 21.9 Laparoscopic view of middle colic vein after
skeletonization and clip application.
Root of mesentery
Superior
mesenteric
artery
Middle
colic
artery
(a)(b)
Superior
mesenteri
c
artery
Middle
colic
artery
Figure 21.7 (See QR 1/4.) Digital image demonstrating the relationship between the middle colic adipovascular pedicle
and the mesenteric root region. (a) View from the right side. (b) View from the left side.
Open transverse mesocolic mobilization and division 305
OPEN TRANSVERSE MESOCOLIC
MOBILIZATION AND DIVISION
e principles here are identical to that of laparoscopic/
robotic mobilization of transverse mesocolon and, similarly,
are entirely mesenteric and peritoneal based. It is usually con-
ducted as part of total mesocolectomy. In keeping with this,
the splenic exure has been detached, the inferior mesenteric
adipovascular artery, and vein divided. As for laparoscopic/
robotic mobilization, a mesenteric margin will be apparent,
which serves as a starting point for transverse mesocolic
mobilization (see the “Mobilization from the le” section).
Mobilizing the greater omentum from the
transverse mesocolon
e greater omentum is attached to the transverse colon and
mesocolon at four points. ese include (1) the omentocolic
refl ction, (2) focal adhesions between the undersurface of
the omentum and the cephalad surface of the mesocolon,
fusion with the (3) hepatocolic peritoneal refl ction and
(4) the splenocolic refl ction. Most surgeons commence
mobilization in the midline with division of the omentocolic
refl ction.
e greater omentum is lied upward placing tension
on the reection between it and the upper surface of the
transverse colon (Figure 21.10). e reection is divided
through and adhesions between the greater omentum and
the cephalad aspect of the transverse mesocolon divided.
Oen the degree of fusion between greater omentum and
underlying mesocolon can hamper identication of the
correct plane of dissection here. If there is doubt, then it is
important to err toward the greater omentum and not into
mesocolon. ere may be some bleeding, but this is usu-
ally controlled with artery clips. If one digresses into an
intramesocolic plane then bleeding is more extensive and
dicult to control. Sometimes nonanatomic dissection
is impossible to avoid. Notwithstanding this one should
always aim to return to the correct plane of dissection as
quickly as is feasible.
Due to the coalescence of greater omentum with the
hepatocolic reection on the right and the splenocolic
reection on the le, it can sometimes be dicult to
identify a plane in these regions. is region of anatomy
is poorly understood and represents an area for future
development.
Mobilization from the left
In general, the surgeon will be approaching from the left side
of the midline, as in a total mesocolectomy. In this case, the
divided edge of the left mesocolon will be apparent and is
an important starting landmark for division (Figure21.11).
e inferior mesenteric vein (IMV) may be apparent and
can be isolated, clipped, divided, and ligated. Isolation of
the IMV again depends on the presence of avascular mes-
entery on either side of it (Figure 21.11). Such is the relative
importance of the free margin of the mesentery on the le
that an illustration from an alternative view point (i.e., from
below to up) is provided in Figure 21.12.
Mobilization from the right
e hepatocolic reection has usually been divided up to
the point at which the greater omentum adheres to it. In
general, coalescence of the two structures is such that they
cannot be separated and the surgeon divides through the
greater omentum. is exposes the upper surface of the
transverse mesocolon. e later is simply detached from
the underlying fascia by mesofascial separation in this
region. is is continued from lateral to medial until fur-
ther detachment is impeded by the mesenteric root region
where the superior mesenteric artery comes through the
pancreas (Figure 21.13).
The mesenteric root region
All that remains for complete mobilization and separation
of the transverse mesocolon is for its division at the mes-
enteric root region. Here, the middle colic pedicle arises
from the superior mesenteric pedicle and passes toward the
transverse mesocolon. e middle colic vessel can give o
the right colic, when this is present (Figure 21.14a), before
it divides into its main branches. In general, it is usually
safest to divide the main branches rather than the middle
Greater omentum
Omentocolic reflection
Transverse colon
Omentocolic reflection (open surgery)
Figure 21.10 Intraoperative view of the omentocolic
reection and its division, thereby partially separating the
greater omentum from the upper surface of the trans-
verse mesocolon.