Sandwich sign | Radiology Signs

Answer:

The sandwich sign is the appearance of confluent mesenteric nodal masses lying anterior and posterior to the mesenteric vessels, with the perivascular fat and the superior mesenteric artery and vein preserved between them like the filling of a sandwich. The nodal tissue is typically homogeneous, of soft tissue attenuation and mildly enhancing, without necrosis or calcification before treatment. The diagnostic value lies less in the shape than in what the encased vessels do: in mesenteric lymphoma the vessels are surrounded but neither narrowed, occluded nor retracted, and the intervening fat stays clean. That behaviour separates it from the two principal mimics. Carcinoid and other desmoplastic mesenteric deposits tether and kink the vessels, spiculate the surrounding fat and usually calcify, producing bowel wall ischaemia and thickening; tuberculous mesenteric adenopathy produces low attenuation nodes with rim enhancement and often ascites and peritoneal thickening. Mesenteric nodal disease occurs in roughly half of non-Hodgkin lymphomas, particularly follicular and diffuse large B-cell subtypes, and is uncommon in Hodgkin lymphoma, so the sign carries subtype information as well. FDG PET/CT is used for staging and response assessment, and image-guided core biopsy rather than fine-needle aspiration is required because subtyping needs architecture.

Why is it called so?

The two slabs of nodal tissue above and below the layer of mesenteric vessels and fat resemble the two slices of bread enclosing a sandwich filling.

Pathophysiology

Lymphomatous nodes in the small bowel mesentery enlarge along the vascular pedicle and coalesce as their capsules are breached, forming a lobulated mass that grows around rather than into the mesenteric vessels. Lymphoma provokes little or no desmoplastic reaction, so the adventitia and perivascular fat are not invaded and the vessels remain patent and straight even when completely enveloped. The tumour is soft and infiltrative, which is why it conforms to the mesenteric leaves instead of displacing them and why bowel obstruction is uncommon despite bulky disease.

Alternative names: Hamburger sign; mesenteric sandwich

Other associated named signs: Misty mesentery, the aneurysmal dilatation sign of small bowel lymphoma, and the spoke wheel pattern of desmoplastic carcinoid metastases

References

1. Karaosmanoglu D, Karcaaltincaba M, Oguz B, Akata D, Ozmen M, Akhan O. CT findings of lymphoma with peritoneal, omental and mesenteric involvement: peritoneal lymphomatosis. Eur J Radiol. 2009;71(2):313-7. PMID: 18513906.