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Chapter 21 (page 98)
Pyloric membrane, web or diaphragm has been defined as a thin, circumferential mucosal
septum in the pyloric region, projecting intraluminally perpendicular to the long axis of
the "antrum". It is composed of two layers of gastric mucosa, with a central core of
submucosa and muscularis mucosae; the external muscular and serous coats do not take
part in its formation. In the majority of cases a central or eccentric aperture is present,
varying from a pinhole to several millimeters in diameter; in a few cases the membrane
was unperforated or complete (Rowling l959; Melamed et al. l960; Gerber l965; Parrish
et al. l968; Felson et al. l969; Bell et al. l977; Mitchell et al. l979; Jinkins et al. l980).
Pyloric membrane is generally regarded as a congenital anomaly. It is usually associated
with symptoms and signs of gastric outlet obstruction. In incomplete membranes
symptoms may only occur in adult life, the aperture preventing obstruction for many
years (Cremin l969; Jinkins et al. l980). The condition has been described in premature
and newborn infants, in older infants and children (Touroff and Sussman l940; Gerber
l965; Farman et al. l968; Cremin l969; Bell et al. l977; Fujioka et al. l980; Jinkins et
al. l980), and in adults (Farman et al l968; Felson et al l969; Melamed et al l960; Ghent
and Denton l974; Ghahremani l974), the ages in adults ranging from 32 to 85 years.
A typical radiographic sign is a radiolucent line 2.0 to 3.0 mm in width, perpendicular to
the long axis of the "antrum", representing the membrane (Felson et al. l969). The region
between the membrane and the pyloric aperture may be filled with barium, resembling
the duodenal bulb; the "double-bulb" appearance is another chracteristic sign (Parrish et
al. l968; Felson et al. l969; Bell et al. l977).
In the great majority of cases described in the literature, the membrane was located 1.0 to
4.0 cm proximal to the pyloric aperture; it could perhaps best be designated a
"prepyloric" membrane in these cases (vide infra). In a few instances it was very close
to, or at the pylorus ("true pyloric membrane"); one case of Rowling (l959), one of
Dineen and Redo (l963), one of Gerber (l965), two of Felson et al. (l969) and one of
Mitchell (l979) fall into this category. In isolated instances (one case of Felson et al., and
one of Ghahremani), a membrane was seen 7.0cm proximal to the pylorus.
In the prepyloric category, the distance of the membrane from the pyloric aperture varied
from 1.0 to 2.0 cm in children (Bell et al. l978), and from 1.5 to 4.5 cm in adults
(Ghahremani l974). The majority of membranes in adults were located at a distance of
1.5 to 4.0 cm from the pylorus (Rowling l959; Melamed et al. l960; Parrish l968;
Cremin l969; Felson et al. l969; Ghahremani l974; Bell et al. l977; Mitchell et al. l979;
Jinkins et al. l980).
We have not encountered reports in which the prepyloric membrane was described in
relation to the pyloric sphincteric cylinder. However, in many descriptions and their
accompanying illustrations, it was noted that the prepyloric membrane occurred in the
location of the left pyloric loop. This is especially well demonstrated in illustrations
accompanying the case report of Rowling (l959), that of Melamed et al (l960), the 3 cases
of Parrish et al. (l968), the 2 of Cremin (l969), the one of Ghent and Denton (l974), most
of the 10 cases of Bell et al. (l977), the 2 cases of Fujioka et al (l980) and the 4 of Jinkins
et al. (l980). It appears to us (but it has not been proved) that, in the majority of cases,
the prepyloric mucosal membrane occurs on the luminal aspect of the left pyloric loop of
the muscularis externa, in the same way as the mucosal and submucosal parts of the
pyloric ring are located on the luminal aspect of the right pyloric loop (to form the pyloric
ring). It is interesting to note that Parrish et al. (l968) found a definite thickening in the
muscularis externa underlying the membrane in one of their cases; this could
conceivably be due to the left loop.
Fujioka et al. (l980) also reported 2 cases of pseudowebs, in whom radiographic
examination had shown typical signs of prepyloric membranes; at operation and
endoscopy no abnormality was found. In these cases the "webs" were probably caused
by prominent, circular mucosal folds. It should be possible to differentiate permanent
webs from circular mucosal folds by the characteristic movements and change in position
of the folds during contraction of the sphincteric cylinder, as discussed in Chapters 2 and
13. However, a circular mucosal fold may occasionally be permanent, simulating a web
- Bell MJ, Ternberg JL, McAlister W, et al. Antral diaphragm: cause of gastric
outlet obstruction in infants and children. J Pediatr l977, 90, 196-
- Bell MJ, Ternberg JL, Keating JP, et al. Prepyloric gastric antral web: a puzzling
epidemic. J Pediat Surg l978, 13, 307-313.
- Cremin BJ. Congenital pyloric antral membranes in infancy.
Radiology l969, 92, 509-512.
- Dineen JP, Redo SF. Pyloric obstruction due to mucosal diaphragm.
Surgery l963, 53, 674-676.
- Farman J, Cywes S, Werbeloff L. Pyloric mucosal diaphragms. Clin
Rad l968, l9, 95-99.
- Felson B, Berkmen YM, Hoyumpa M. Gastric mucosal diaphragm.
Radiology l969, 92, 513-517.
- Fujioka M, Fisher S, Young LW. Pseudoweb of the gastric antrum in infants.
Ped Radiol l980, 9, 73-75.
- Gerber BC. Prepyloric diaphragm, an unusual abnormality: a case report.
Arch Surg l965, 90, 472-480.
- Ghent CN, Denton D. Mucosal diaphragm of the gastric antrum: case report and
review of the literature. Canad J Surg l974, 17, 274-278.
- Ghahremani GG. Nonobstructive mucosal diaphragms or rings of the gastric
antrum in adults. Amer J Roentg Rad Ther Nucl Med l974, 121, 236-
- Jinkins JR, Ball TI, Clements JL, et al. Antral mucosal diaphragms in infants and
children. Ped Radiol l980, 9, 69-72.
- Melamed A, Haukohl RS, Callan E. Pyloric antral mucosal diaphragm with
transpyloric mucosal prolapse. Radiology l960, 74, 452-457.
- Mitchell KG, McGowan A, Smith DC, et al. Pyloric diaphragm, antral web,
congenital antral membrane: a surgical rarity? Brit J Surg l979, 66,
- Parrish RA, Kanavage CB, Wells JA, et al. Surg Gynaec Obstet l968,
- Rowling JT. The prepyloric septum: a rare anomaly. Brit J Surg
l959, 47, 162-166.
- Touroff ASW, Sussman RM. Congenital prepyloric membranous obstruction in
premature infant. Surgery l940, 8, 739-755.
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