The anatomy of a heart, and a water bottle

by Lorien E. Menhennett

As I explained in my last post, medical descriptions are sometimes a little … strange. Some of them, as I learned yesterday, are also generation-dependent.

I was sitting at my desk after a long day in the hospital, studying for my medicine shelf exam (aka final exam). While doing cardiology review questions on my laptop, I came across a scenario in which a woman had a pericardial effusion. Essentially, this is a collection of fluid surrounding the heart. The chest x-ray was described as showing a “‘water bottle’ heart shape.”

Below is an image I found online that’s similar to the one from my practice question. Think about your conception of a water bottle, then look at the image.

This is the chest x-ray of a patient with a pericardial effusion.

Staring at my laptop screen, I thought to myself, “This doesn’t look like any water bottle I’ve ever seen.” I tried to think creatively, how one might fit a Fiji, Evian, or Aquafina bottle into that globular shape. Try as I might, I failed.

So I Google-image-searched this phrase: “pericardial effusion water bottle silhouette.” Most of the images that came up looked just like the one above. That didn’t help me. But when I found this image on Radiopaedia, an online collection of radiology cases, (see below) the analogy suddenly made sense. Whoever first compared the heart silhouette in a pericardial effusion to a water bottle probably never saw a plastic, disposable water bottle, like the ones we use today. His (and it was most likely a “he” since most doctors were men back then) conception of a water bottle was very different from mine. As Radiopaedia explains, “The fluid-filled pericardial sac casts a cardiac silhouette that resembles an old-fashioned leather water bottle.”

The “water bottle-shaped heart” in pericardial effusion explained, with a visual aid. From Radiopaedia.com.

I initially felt satisfied with my investigation, but the journalist in me cried out for confirmation from a second source. So I went back to Google images, digging a little deeper. And I found these:

This interpretation of “water bottle” was quite different. I don’t really consider these glass bottles “water bottles” in the same way I do both the plastic bottles of today and the old-fashioned leather bottle in the Radiopaedia image. But then again, what do I know? Maybe around the time x-rays were first being used clinically, in the late 1890s, the vessels above were considered “water bottles.” I’m a little skeptical of this, but the image with the greenish x-ray and the clear glass bottle comes from a well-respected medical journal, BMJ Heart. So it’s hard to discount this comparison completely.

To try and come up with a little more information, I Googled the same phrase “pericardial effusion water bottle silhouette” to look at text results too. The seventh result was a 2016 article from an international emergency medicine journal. The article is called “Message in a bottle: The use of chest radiography for diagnosis of pericardial effusion.” I didn’t read the entire article (I was studying for a test, remember?) but I did skim it, looking for “water bottle” references. The whole article is about using the “water bottle sign” to clue you into the presence of a pericardial effusion, and to help you decide whether to perform advanced imaging. The article actually refers to the water bottle sign 12 times. But not once does the article explain how this image looks like a water bottle, only that it does.

I am still studying for my test (I’ve got 48 hours left to master the field of internal medicine). So I must stop my descent into the rabbit hole of this question. Perhaps someone, somewhere in the world, still uses a water bottle that resembles the globe-shaped heart seen in a pericardial effusion x-ray. Perhaps that person would understand this arcane medical reference. But for the most part, at least to those of us in medicine who are using this reference today, it is outdated. It lives on, though, because as much as medicine is about progress, it is also about history.

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