External hemorrhoids swollen but not thrombosed - why not drain on their own?

Question

I've used web search and have read now quite a number of articles on hemorrhoids, the key info as far as I understood:

1. hemorrhoids / haemorrhoids term is used to refer to both decease (HD from now on) and anatomical hemorrhoidal fibrovascular cushions / anal cushions.
2. everybody is talking about how to get rid of them and how long they persist. Definitive cause is not known and I have not found any info on how quickly/long HD forms.
3. many articles contain classification: internal and external and 4 degree classification of severety. Some have info that 4 degree classification is for internal HD.
4. thrombosis is complication and it is not that common.

Note: I've already closed a lot of tabs in web browser, maybe add links later if needed / beneficial.

Hemorrhoids are fibrovascular cushions containing arteriovenous communications that are located in the subepithelial space of the anal canal and are a normal part of human anatomy. (Thompson WH. The nature of hemorrhoids. Br J Surg 1975; 62:542–52.) They are separated into internal and external hemorrhoids based on location above or below the dentate line, respectively. There are three primary cushions located in the left lateral, right anterior, and right posterior quadrants, each with an internal and external component, for a total of six primary hemorrhoidal cushions: three internal and three external. (THE AMERICAN SURGEON, August 2009, Hemorrhoids: Diagnosis and Current Management, SHAUNA LORENZO-RIVERO, M.D.)

I was trying to find out more about cushions anatomical structure via web search but as of now I mostly find about hemorrhoid ailments instead.

Qs:

1. I don't understand what if not blood clots prevents blood from leaving external hemorrhoid cushions after person leaves the toilet.

2. Is there an info on how quickly/long HD forms, how it progresses usually with time (especially external)?

Also everywhere HD classification is by degree of protrusion. But external hemorrhoid pathology is out of anorectum, does it really mean it is of 4th degree?

P.S. symptomatic hemorrhoids is very common, I found surprising on this site there is still no tag for it (same for "rectal", "anorectal" tags).

Answer 1

The fibrovascular cushions you describe are part of normal anal anatomy and are sometimes called haemorrhoid cushions.

Haemorrhoid, as a noun, is usually used to refer to a pathological condition with enlargement of this tissue and the presence of symptoms.

I'm not quite sure exactly what your question "I don't understand what if not blood clots prevents blood from leaving external hemorrhoid cushions after person leaves the toilet." refers to. Blood does leave the cushions, to some extent, after straining ceases and the pressure in the anal area is reduced. Some blood would remain in these tissues but the blood that built up during straining would then return to the rest of the vascular system.

If you mean why would haemorrhoids remain enlarged and symptomatic if no clot is present, this would be due to relatively persistant changes to the tissue due to the swelling, with enlargement of the vascular spaces.

4th Degree haemorrhoids referred to haemorrhoids that do not return spontaneously into the anus after defecation nor can they be returned by manual pressure.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3342598/