A large volume of extracellular mucin with embedded malignant glands is seen dissecting into muscularis of the bladder.
Variable cellularity of the glandular component can be appreciated here. Although enteric histologic subtype (resembling colonic adenocarcinoma) often have mucin as a component, the mucinous or colloid subtype has much more prominent mucinous background.
The mucinous or colloid subtype consists of glands embedded in pools of mucin. Signet ring cells may be seen mucinous carcinomas, however, to classify the tumor as 'signet-ring', the tumor must be composed almost entirely of signet ring cells or poorly differentiated cells with intracytoplasmic mucin.2 It is important to make this distinction because signet ring carcinomas carries a very grim prognosis.
Primary vesical adenocarcinomas are rare, accounting for approximately 2% of all bladder cancers. These neoplasms are broadly divided into urachal and non-urachal categories, depending on whether or not the neoplasm is associated with the urachus (which connects the bladder to the allantois in the developing fetus - yes, time to dig out that embryology textbook from medical school).
Both urachal and non-urachal bladder adenocarcinomas have several histologic subtypes. For non-urachal adenocarcinomas, the histologic subtypes are listed as follows in the order of frequency: adenocarcinoma NOS, signet-ring, enteric, mucinous and signet-ring. Interestingly, urachal adenocarcinomas have a different order of frequency, with mucinous and enteric histologic types being the most common, followed by the mixed subtype, signet-ring subtype and adenocarcinoma NOS.1
Grossly, the bladder wall may be thickened due to the infiltration of signet ring cells, giving a 'leather bottle' look to the bladder, also known as linitis plastica. Note that this imagery refers to leather bottles of olden times.
For a more comprehensive discussion of bladder adenocarcinomas, please visit our case for this entity (see link below).
1 Mills SE, ed. Sternberg's Diagnostic Surgical Pathology.4th Ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2004: 2060-2062.
2 Fletcher CDM, ed. Diagnostic Histopathology of Tumors. 3rd Ed. Philadelphia, PA: Elsevier; 2007: 539-543.