Shunt Insufficiency

Definition

Shunt insufficiency is a pathological change in the esophagotracheal fistula (= the shunt), as the consequence of which fluid escapes from the esophagus into the trachea, along/around the voice prosthesis. There is no adequate seal between the esophagotracheal fistula and the voice prosthesis.

Frequency:13-27% of all voice prosthesis changes (27% Laccourreye O. et al. (1997), 13% Op de Coul BM et al. (2000), 26% de Raucourt D. et al. (1998)

Ill. A. The shunt is swollen, with the flange of the voice prosthesis cutting in.

Iii. B. Following removal of the voice prosthesis, it can be seen that necrotic tissue developed (1) under the compression by the prostheses flanges.

Ill. C: Dilated atrophic shunt, wall thickness 3 mm, and in the typical “pear-shape”.

Ill. D: Dilated atrophic shunt, 3 mm wall thickness on the cranial circumference and 6 mm on the caudal circumference.

Pathophysiology

We differentiate between two types of shunt insufficiency: the infected necrotic shunt, and the dilated atropic shunt.

Infected necrotic shunt

An infected necrotic shunt occurs acutely as the result of a local infection of the shunt and prosthesis. The swelling of the shunt leads to a compression of the shunt tissue between the flanges of the voice prosthesis (ill. A), which results in necroses of the shunt tissue. Leakage occurs as these necroses break down.

Development of an infected necrotic shunt

A: The voice prosthesis is correctly positioned in the shunt.

B: The shunt swells, e.g. as the result of an infection. The flanges of the voice prosthesis are pushed to the outside, exerting pressure on the shunt tissue.

C: If the flange of voice prosthesis presses against the shunt tissue, this will result in necrosis of the shunt tissue between the flanges.

D: The necrotic shunt tissue is broken down by infection. The shunt becomes unstable and no longer seals properly. This results in periprosthetic leakage. The voice prosthesis may be lost.

Dilated atrophic shunt

The dilated atrophic shunt occurs slowly, often after many years of the voice prosthesis being used without problems. The shunt gradually becomes thinner, until the voice prosthesis is no longer sealed properly. Prosthesis lengths of 4 mm and less are not unusual. In some cases, systemic causes may be found for shunt atrophy (poorly managed Diabetes mellitus, tumor recurrence, cachexia, hypothyroidism etc.). If the systematic disease is successfully treated, the shunt situation usually also improves.

Development of a dilated atrophic shunt

E: A healthy shunt seals perfectly against the voice prosthesis.

F: The shunt atrophies. The voice prosthesis is loose, and shorter ones are constantly chosen in order to provide an adequate seal.

G: Continued atrophy results in dilation of the shunt. Very short prostheses do not seal properly either. The result is periprosthetic leakage.

Table comparing the two types of shunt insufficiency

Shunt type	Infected/necrotic shunt	Dilated/atrophic shunt
Pathology	Infection, swelling, pressure by the prosthesis flange, necroses	Atrophy, scarring, dilation of the shunt
Occurrence	Acute, e.g. in cases of infection, radiotherapy or following surgery	Slowly following unproblematic prosthesis performance
Prognosis	Good, often a one-off occurrence	Moderate, often chronic problem
Frequency	~50% of all periprosthetic leaks	~50% of all periprosthetic leaks

Symptoms of shunt insufficiency

The main symptom of shunt insufficiency is periprosthetic leakage when attempting to swallow. It shows that rather than the voice prosthesis being responsible for the leak, the shunt is in fact not closing properly around the prosthesis. Often, an examination will reveal a widening, inflammation or necrosis of the shunt. Even short-term prosthesis losses should be followed by examination of the shunt to establish its stability.

Diagnosis of shunt insufficiency

If a periprosthetic leak occurs when the patient attempts to swallow and the voice prosthesis is of the correct length, or if the insertion of a correctly measured voice prosthesis fails to remedy a periprosthetic leak, then the shunt is insufficient. In line with the above criteria, clinical examination and anamnesis will enable the practitioner to differentiate between an infected necrotic and a dilated atrophic shunt.