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7 Cellular Anatomy of the Mesentery 57
connective tissue is primarily composed of elastin helices. It is feasible the helical
shape of these facilitates return to a normal conformation following stretch.
No studies to date have examined the regions where the reflection arises from the
parietal peritoneum and continues as the visceral. One of the reasons for this lies in
the fact that the peritoneum is continuous, and there are no anatomical landmarks
that precisely define specific regions.
Histology of Toldt’s Fascia
Wherever an organ comes into close proximity with the abdominal wall it does not
fuse directly with the wall. Instead, a connective tissue occurs between the organ
and the abdominal wall. This is Toldt’s fascia. Although flimsy and variable in
composition it is a universal finding that likely contributes to maintaining the organ
in position.
Few studies have examined the fascia in detail. The connective tissue composition remains to be confirmed but it would appear from early findings that it is
comprised of loose connective tissue. Culligan et al. examined the fascia and found
that in 30% of cases it contained lymphatic channels. This is highly relevant as it
indicates that it plays a role in fluid absorption.
The relationship between the fascia and mesentery extends beyond simple
adhesion. It appears to coales ce with the connective tissue surrounding the major
vessels as these enter the mesentery. Given that this connective tissue is also
continuous with that of the lattice contained within the mesentery, it means there is
a continuity between mesenteric, adventitial and fascial connective tissue. The
scientific and clinical relevance of this continuity remains to be determined.
The Mesentery in Disease States
Changes in disease states are described in detail elsewhere but will be briefly
discussed here. Several disease states lead to an alteration in the histology of the
mesentery. Again, findings here can also be considered as preliminary and requiring
further characterization. For example, the surface of the mesentery is altered in
peritoneal carcinomatosis in which peritoneal deposits arise in a sporadic distribution. These deposits extend into the mese ntery to a limited degree but never
appear to penetrate deep into the substance of the mesentery (i.e. they are not
locally invasive). It is not known whether peritoneal deposits are distributed in this
manner nor is it known why (despite having an apparent capacity of spread) they
are not locally invasive.
The surface mesotheluim of the mesentery is substantially altered in mesenteric
sclerosis in which there is pronounced fibrosis and thickening. The factors involved
are under intensive investigation as this phenomenon frequently leads to failure of
58 M. G. Kiernan and J. C. Coffey
peritoneal dialysis in patients with renal failure. Mesenteric panniculitis is characterized by mesenteric infiltration with acute and chronic inflammatory cells.
There are a number of subtypes but as with sclerosis, the etiology and pathophysiology remains to be elucidated.
.
Future Directions
It is essential to characterize the region where the mesentery intersects all
abdominal digestive organs. This is particularly important as, given continuity, any
signal that passes from one to another must pass through this region. As such to
date it is virtually unchartered in terms of what is known about it.
Suggested Reading
1. Culligan K, Walsh S, Dunne C, Walsh M, Ryan S, Quondamatteo F, Dockery P, Coffey JC.
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–
56. https://doi.org/10.1097/SLA.0000000000000323. PMID: 24441808.
Part III
Diagnostic Procedures
Radiography of the Mesentery
Scott Sorensen and Abraham H. Dachman
Plain Films of the Abdomen
Description of Procedure
Plain films of the abdomen are often the first exam done for abdominal symptoms.
They are readily available, inexpensive and can be tailored to the clinical question.
Indications
Common indications are abdominal pain, clinical concern for ileus versus
mechanical obstruction, constipation to evaluate for stool burden, to search for
signs of ischemia or perforation and position and location of radiopaque objects
such as tubes and catheters.
8
Complementary Procedures
Since plain films are often non-specific or non-diagnostic, CT is the most common
alternate complimentary procedure.
Contraindications
There are no absolute contraindications to plain radiography. However it is
advisable to minimize the use of ionizing radiation in general and a greater level of
S. Sorensen A. H. Dachman (&)
The University of Chicago, MC 2026 5841 S. Maryland Ave., Chicago, IL 60637, USA
e-mail: ahdachma@uchicago.edu
© Springer Nature Switzerland AG 2021
E. D. Ehrenpreis et al. (eds.), The Mesenteric Organ in Health and Disease,
https://doi.org/10.1007/978-3-030-71963-0_8
61
62 S. Sorensen and A. H. Dachman
caution should be used for children, women of child bearing age, and all young
individuals. When doing portable radiography, there is often a small amount of
scatter radiation to surrounding patients, e.g., in the setting of a shared room such as
an open ICU. Views such as cross table lateral views shoul d be avoided in circumstances where adjacent patients will be exposed.
Preparation of Patient
No patient preparation is needed for plain radiographs. Overlying radiopaque
objects should be removed such as clothing and jewelry.
How the Procedure Is Performed
The procedure is normally performed by a technologist. Images can be obtained in
various ways depending on the indication. Supine, prone, right and left side down
decubitus views, recumbent or erect lateral views, cross-table lateral views are some
common examples.
Typical Abnormal Findings
Depending on the disease process, plain films might show ileus, obstruction,
intramural air, free intraperitoneal air, extrinsic compression from a mesenteric
mass or abnormal location due to internal hernia. Several examples are shown
throughout the book.
Complications
None.
Computed Tomography (CT)
Description of Procedure
Computed tomography (CT), has become the mainstay for evaluation of peritoneal
and mesenteric disease. X-rays passing through the body to a set of detectors is used
to create helical images that are reconstructed in the axial, coronal and sagittal
planes. Three-dimensional reconstructions can be used to depict disease and the
relationship of mesenteric structures.
8 Radiography of the Mesentery 63
Indications
Most suspected mesenteric diseases can be imaged with CT.
Complementary Procedures
Plain films and MRI are the main complementary procedures, although ultrasound
can be complimentary to look for fluid collections in the peritoneal cavity. Compared to MRI, CT is less expensive, and less sensitive to patient movement. It can
be performed in patient with implanted medical devices that might preclude MRI
examinations.
Contraindications
There are no absolute contraindications.
Relative Contraindications
Radiation should be minimized or avoided in children, pregnant women and young
patients. Some patients are claustrophobic and have trouble if the face or upper
chest is in the gantry. This can be avoided for most CT of the abdomen and pelvis.
Intravenous contrast is relatively contraindicated in patients with reduced renal
function, old age or known long standing conditions that may diminish renal
function. In some cases, a reduced volume of contrast may be used.
Intravenous contrast is iodine based and patients may have allergic reactions.
When necessary, patients can be pre-medicated with steroids and antihistamines.
This pre-medication usually commences 12 hours prior the administration of
contrast.
Preparation of Patient
Metal objects that might affect the scan should be removed. Most patients are asked
to not eat or drink for several hours prior to the scan. When oral contrast is used, it
is administered about 1 or more hours prior to scan.
How the Procedure Is Performed
CT can be performed in different phases: pre-intra venous contrast, post intravenous
contrast in standard portal venous phase or as a CT angiogram in the arterial phase.
Delayed excretory phase can be performed when needed. Oral contrast can be either
64 S. Sorensen and A. H. Dachman
omitted or used as needed, although most non-emergent CT is done with oral
contrast. CT enterography is a specialized study using low density contrast to
distend the entire small intestine.
Scans are fast and require only a short breath hold. The patient must lie still to
avoid motion artifacts. The contrast injection lasts for 10–30 seconds and might
produce a warm, flushed sensation and a metallic taste in the mouth that lasts a
minute or two.
Typical Abnormal Findings
Specific diseases are shown through this book.
Complications
Intravenous contrast can result in allergic reactions, usually mild. Severe allergic
reactions are uncommon. Extravasated contrast in the arm may occur when there is
poor venous access. Transient diminished renal function can occur especially in the
elderly and in patient with underlying renal damage.
Additional Comments
Note that much has been written about the theoretical risk of radiation from CT.
There is no conclusive evidence that radiation at small amounts delivered by a CT
scan causes cancer. Nevertheless, the good practice principles of using radiation
doses “as law as is reasonably achievable” aka “ALARA” should be employed.
Modern scanners now have many different methods to reduce patient radiation dose
compared to those just a few years earlier.
Magnetic Resonance Imaging (MRI)
Description of Procedure
MRI uses magnetic fields and electric filed gradients to generate images of the
body. Unlike CT it does not employ ionizing radiation. It has the advantage of
providing good soft tissue contrast. It is therefore commonly used to evaluate
organs of the abdomen and in the context of this book, inflammatory bowel disease
and vasculitis. Often, intravenous contrast agents are used.
8 Radiography of the Mesentery 65
Contraindications
There are many contraindications including certain types of metal in the body that
might move when exposed to strong magnetic fields.
Relative Contraindications
Claustrophobic patients may not be able to tolerate an MRI without sedation. Some
so-called ‘open’ MRI scanners can be used at the expense of image quality. Patients
with impaired renal function may be unable to undergo contrast enhanced scans.
Generally pregnant women in the first 3–4 months of pregnancy should avoid MRI.
Breast feeding women who receive intravenous contrast should pump breast
milk before the study and wait about 24 hours before breast feeding.
Preparation of Patient
Some items need to be removed before going into the MRI room, e.g., cards with
magnetic strips, electronic devices, hearing aids, watches, metal jewelry, hairpins,
etc. Some cardiac pacemakers, aneurysm clips and neurostimulators are MRI
compatible and some are not.
How the Procedure Is Performed
The patient lies on a table with a narrow bore gantry and undergo es several scans
that can take 15–45 minutes (sometimes up to an hour) depending on the nature of
the scan. Common pulse sequences are T1 weighted, T2 weighted, proton density
weighted, gradient echo, inversion recovery diffusion and perfusion weighted and
MR angiography (MRA). MRI fluoroscopy sequences can be used in some cases.
Typical Abnormal Findings
Several examples of mesenteric disease depicted with MRI are shown in this book.
Complications
Renal function can be impaired by intravenous contrast agents such as Gadolinium.
Inadvertent use of MRI in patients who have internal metallic objects can also have
consequences.
66 S. Sorensen and A. H. Dachman
Conventional Angiography
Description of Procedure
Catheter angiography is performed suing X-ray guidance on fluoroscopy and
catheterization of a vessel to permit injection of iodinated contrast. In the case of
abdominal disease, a femoral route is commonly used to access the aorta or inferior
vena cava depending on whether an arterial or venous injection is needed. Rapid
sequential images are obtained during the injection of contrast.
Indications
Angiography can be done for diagnostic or therapeutic purposes. In the case of
mesenteric disease the vascularity and organ of origin of a mass can be determined.
Vasculitis, aneurysms, dissection and arteriovenous malformations involving single
or multiple vessels can be diagnosed. Bleeding can be treated with coil
embolization.
Complementary Procedures
CT and MR angiography often supplant the need for conventional angiography.
Contraindications
Severe bleeding diathesis.
Preparation of Patient
Patients should not eat for about 12 hours prior to the exam. They should remove
metallic jewelry, etc. Medications that affect bleeding are usually withheld. The
same concerns for reactions to iodinated contrast for CT apply. Likewise, breastfeeding should be withheld for about 24 hours after the test. Sedation is often used
and thus patients should be accompanies and not drive themselves home.
How the Procedure Is Performed
A sterile room is used to perform angiography. The radiologists wear gowns,
masks, hats and gloves similar to an operating room. A catheter is inserted via a
small skin incision into a blood vessel. The machine consists of a table for the
8 Radiography of the Mesentery 67
patient and one or two X-ray tubes, which can be positioned around the patient.
Video monitors display the images produces.
A technologist and radiologist work together to insert an IV line, sterilely prepare the skin at the site of catheter placement and place the catheter. The radiologist
will manipulate the catheter into the desired position before the contrast material is
injected. After the procedure the catheter is removed and pressure is applied to the
site for 10–20 minutes. The procedure may take 1–2 hours.
Complications
As with surgery, complications can be mild or sever and include pain, bleeding and
infection. There may be allergic reactions to the iodinated contrast and effects on
renal function. Blood clots can form on catheters and dislodge.
PET Scan
Description of Procedure
Positron emission tomography (PET) uses radioactive agents (radiotracers), a
detection camera and computer to study the tissue function of organs and tumors.
Indications
In the case of mesenteric disease, there are few specific disease processes that can
benefit from PET scanning, in particular searching for carcinomatosis or metastatic
disease elsewhere for primary tumors known to be PET avid.
Complementary Procedures
Conventional imaging can often stage neoplastic disease without the need for PET.
Relative Contraindications
Some claustrophobic patients have anxiety.