It can occur due to infiltration of the mesenteric fat with inflammatory cells,
fluid (oedema,
lymph,
blood),
malignant cells and fibrosis
In the normal mesentery,
the blood vessels are clearly visualised due to low attenuation of the mesenteric fat
In case of misty mesentery,
the vessels lose their sharp interfaces and may be partially / completely effaced; Typical features include a left-sided distribution,
a ‘fat halo’ sign,
nodules and a pseudotumorous hyperdense stripe.
Mildly enlarged lymph nodes are seen,
calcification may rarely be seen.
It is associated with malignancy,
surgery,
infection,
autoimmune conditions and trauma
Thrombosis of the superior mesenteric vein may be associated with increase in fat density,
probably due to oedema
Conditions causing misty mesentery appearance on CT scan:
Oedema – heart failure, hypoalbuminemia,
portal hypertension,
inferior vena cava obstruction
Inflammation – pancreatitis,
appendicitis,
inflammatory bowel disease,
diverticulitis
Haemorrhage / trauma
Neoplasms – lymphoma,
pancreatic carcinoma,
colonic carcinoma,
breast carcinoma,
GIST,
carcinoid
Idiopathic – mesenteric panniculitis
Lymphoedema due to obstruction of lymphatics
A ‘Misty mesentery’ is a non-specific finding on CT scans and a cause for this should be sought.
CT changes consistent with mesenteric panniculitis include positive findings; a left-sided distribution,
‘fat-halo’ sign,
pseudotumorous hyperattenuation stripe,
nodules and the absence of features suggesting haemorrhage,
neoplasia,
lymphoedema.
Mildly enlarged lymph nodes are seen,
calcification may rarely be seen.
It may be surrounded by a hypoattenuated fatty "halo sign" and a surrounding hyperattenuating pseudocapsule
It has been suggested that there are two pathological subgroups: Mesenteric Panniculitis ,
representing the very large major subgroup where inflammation and fat necrosis predominate and Retractile /Scelrosing Mesenteritis {rare},
where fibrosis and retraction predominate,
with mass lesion and areas of calcification,
it may coexist with malignancies including lymphoma,
breast,
lung & colonic cancer,
melanoma.
Findings could be identical changes seen in carcinoid tumour.
Mesesentric panniculitis is an inflammatory infiltration of the mesentery with variable mesenteric inflammation.
The prevalence of mesenteric panniculitis on CT scans is around 0.6%,
usually seen in patients over 50 years of age{though two of our patients were 40 years old},
slight male predominance.
It is usually self-limiting,
however,
follow up studies are usually recommended.
The radiological diagnosis of mesenteric panniculitis is based on classical CT signs: the presence of a well-defined "mass effect" on neighbouring structures constituted by mesenteric fat tissue of inhomogeneous higher attenuation than adjacent retroperitoneal or mesocolonic fat and containing small soft tissue nodes (sign}..
The differential diagnosis includes all disorders that can affect the mesentery.
The most common ones are lymphoma,
well-differentiated liposarcoma,
peritoneal carcinomatosis,
carcinoid tumor,
retroperitoneal fibrosis,
lipoma,
mesenteric desmoid tumor,
mesenteric inflammatory pseudotumor,
mesenteric fibromatosis and mesenteric edema.