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Journal of the Anatomical Society of India

Suspensory Muscle of Duodenum: In Human Foetuses of Manipuri Origin

Author(s): Singh, N.S; Singh, M.S; Devi, N.D; Singh, Y.I.

Vol. 52, No. 2 (2003-07 - 2003-12)

Department of Anatomy, Regional Institute of Medical Sciences, Imphal, Manipur. INDIA

Abstract

The gross anatomy and histology of the suspensory muscle of duodenum were studied in 50 human foetuses ofManipuri origin, 34 males and 16 females, in the ages of 21 weeks to 40 weeks.

Abdominal cavity of each foetus was opened. After gross anatomical observation, the suspensory muscle complex of duodenumwas removed en-bloc and fixed in Bouin's fluid. Serial paraffin sections, 5 micrometers thick, were prepared and stained alternately withHaematoxylin and Eosin, Van Geison's, Masson's Trichrome, and Voerhoff's Haematoxylin stains.

Morphologically two distinct structures: (a) Accessory muscle (der Hilfmuskel) and (b) Suspensory muscle of duodenum were identified, occupying cranial and caudal positions respectively. From 28 weeks onwards, an intermediate fibrous zone began to form but didnot develop into a true tendon even at full term. Light microscopy showed presence of skeletal muscle fibres in the accessory muscle, in allspecimens. In the suspensory muscle of duodenum, smooth muscle fibres were detected from 27 weeks onwards, developed further withgrowing age and were continuous only with outer longitudinal muscle coat of the duodenal wall. Considerable amounts of connective tissuefibres were demonstrated but elastic fibres were not seen except in the wall of blood vessels.

Thus, Accessory muscle and suspensory muscle of doudenum are separate entities. No intermediate tendon is formed. Accessorymuscle is striated, while suspensory muscle of duodenum contains smooth muscle fibres continuous only with outer longitudinal musclelayer of the duodenal wall. No elastic fibres can be seen in the intermediate fibrous zone.

Key words: Der Hilfmuskel, duodeno-jejunal flexure, coeliac artery, superior mesenteric artery, crus of diaphragm and duodenum.

Introduction:

Hodson (1908) opined that Manipuris, the indigenous people of Manipur, India, are totally distinct. He further quoted Dr. Brown (1874) as stating that the general facial characteristics of the Munniporie (Manipuri) are of Mongolian type and are decidedly a muscular race. There is no recorded report on the study of the suspensory muscle complex of duodenum amongst this idigenous people.

Treitz (1853) was reported to have pioneered the description of the Suspensory Muscle of Duodenum (SMD) as a structure extending from duodenojejunal flexure to fibrous tissues surrounding the root of Coeliac and Superior mesenteric arteries (Jit, 1952). Treitz (1853) further described the presence of the Accessory muscle (AM) or der Hilfmuskel, extending from the oesophageal opening of diaphragm to the region of the cranial end of SMD. Most of the works were conducted on human adults. Very few workers studied the SMD during its developmental stages in human foetuses and early neonatal period. Jit (1952), Zypen & Revesz (1984) and Hola (1994) studied the structure in human foetuses having age ranges from embryonic stage to full term, but with different opinions.

Jit (1952) reported that the SMD and AM were different entities particularly in the early foetal life, but after 25 weeks collagenous bundles joined the two muscles without forming an intermediate tendon.

Hola (1994) had named it "the suspensory muscle complex" and described it as having two parts: the suspensory muscle proper caudally and the AM cranially. Some connections between the two parts were reported in 6 females and 3 larger male foetuses. Controversy still remains on whether the AM and the SMD are two distinct entities as suggested by Jit (1952); or are they two parts of a single identity (suspensory muscle complex) as suggested by Holla (1994). Most of these workers have reported that the SMD, histologically, contains smooth muscle fibres having continuity with smooth muscle coats of the duodenal wall; while the AM contains skeletal muscle fibres.

The present study assays to find out the morphology and histology of the suspensory muscle complex of the duodenum in various stages of development of the human foetuses of Manipuri origin.

Materials And Methods:

Fresh 50 foetuses, 34 males and 16 females, free from any gross anatomical abnormality, ranging from 21 weeks to 40 weeks (155 mm to 450mm-CR length), were collected from the Department of Obstetrics and Gynaecology, RIMS, Imphal which were the products of terminated pregnancies under the Medical Termination of Pregnancy Act of India, 1971. All the specimens were preserved in 10% Formol-Saline for 10 days. Gestational ages were estimated from obstetrical history and Crown-rump (CR) lengths. The foetuses were divided into 5 groups of 21-24, 25-28, 29-32, 33-36 and 37-40 weeks of age, each group having 10 foetuses.

The abdominal cavity of each foetus was opened; loops of the small intestine traced proximally and duodenojejunal flexure located. Different parts of the duodenum were exposed and studied for the attachments of SMD. The liver was removed piecemeal and the two crura of diaphragm studied for attachments of the AM. The roots of the coeliac and superior mesenteric arteries were located and studied for attachments of caudal and cranial ends of the AM and the SMD, respectively.

The AM and SMD were removed en bloc from all the foetuses and fixed in Bouin's fluid. After embedding in paraffin, 5 micrometers thick serial sections were cut longitudinal to the SMD in the parasagittal planes. Sections were stained alternately with Haematoxylin & Eosin, Van Geison's, Masson's Trichrome, and Voerhoff's Haematoxylin stains for differentiation of muscle fibres, collagen fibres and elastic fibres. The methods described by Kieman (1999) were followed throughout the histological procedures. The stained sections were studied under different magnifications of an Olympus Trinocular Research Microscope (CH40RF200) and photographed.

Observations and Results:

The SMD was demonstrated in 47 foetuses of 22 weeks to 40 weeks, except in 3 foetuses of 21 weeks. The AM could be identified in all the cases.

Gross Morphology:

In 3 foetuses of 21 weeks, the sites for the SMD were occupied by underdeveloped loose and diffuse connective tissue without proper shape and structure. However, at 22-23 weeks, an anlage of the forthcoming structure could be recognised. From 24 weeks onwards, a triangular structure attached caudally to the 3rd and 4th parts of duodenum and cranially to the connective tissues around the root of superior mesenteric artery (RSMA) could be identified in all the remaining cases. The caudal attachment showed extensions to the 2nd part of duodenum in 4 foetuses of 32, 34, 36 and 38 weeks and also to the duodenojejunal flexure in 16 (32%) foetuses of 28 to 40 weeks. Its cranial attachment also showed extensions to the connective tissues around root of coeliac artery (RCA) in 21 (42%) foetuses of 24 to 40 weeks.

The AM could be identified in all the 50 foetuses extending from the right crus of diaphragm cranially, to the RCA caudally. Its cranial end had additional attachment to the left crus of diaphragm in 6 (12%) foetuses of 36-40 weeks; while caudally its attachment extended to RSMA in 21 (42%) foetuses of 24-40 weeks.

The fibrous extensions interconnecting the two entities became progressively prominent from 28 weeks in 21 (42%) foetuses, but remained diffusely distributed. There were no signs of tendon formation.

Microanatomy of SMD:

At 27 weeks (240mm CR length) a few small bundles of smooth muscle fibres could be detected near the duodenal wall supported by an abundant amount of loosely arranged collagen fibres (Fig. No.1). In specimens of 36-40 weeks, the smooth muscles were more prominent and continuous with the outer longitudinal muscle coat of duodenal wall, but not with the inner circular layer (Fig. No.2). Blood bessels were seen in the SMD and elastic fibres could be detected in the wall of larger blood vessels only (Fig. No.3).

Microanatomy of AM:

The AM was composed of skeletal muscle fibres supported by collagenous fibre bundles and was demonstrable by light microscope in all the specimens examined.

Discussion:

Grobler (1977) and Snell (1981) observed that the SMD was a simple fold of peritoneum from the right crus of diaphragm to the duodenojejunal flexure. Jit (1952) and Holla (1994), however, reported two separate structures: the AM and the SMD proper. Zypen and Revesz (1984) also described it as a single structure and demonstrated a narrow mid-portion of fibrous tissue in newborns.

Two separate and distinct entities, the SMD and the AM were observed in this series. The AM or der Hilfmuskel, was recognizable from 21 weeks, which developed and differentiated into a distinct form by 40 weeks. The primordium of SMD was demonstrable from 22 weeks and progressively grew into a definite form by 40 weeks. Gray, (1918) described that it commenced from the connective tissue around the coeliac artery and left crus of diaphragm only. however, in this study, the AM or der Hilfmuskel arose from the right crus of diaphragm in all the 50 cases with additional attachment to the left crus in 6 cases (12%) only. Extension of the caudal attachment of SMD from the 3rd and 4th parts of duodenum to duodeno-jejunal flexure occurred in 16 (32%) cases at an increasing rate with the advancement of foetal age. The fibrous tissue, interconnecting the SMD and the AM, did not develop into a definite tendon even at full term.

Histological findings of the present study were similar to those of Jit (1952), Zypen & Revesz (1984) and Holla (1994). Microscopically, smooth muscle fibres could be detected at an earlier age of 27 weeks, instead of at 28 weeks (Jit, 1952). The smooth muscle fibres were continuous with the outer longitudinal muscle layer of the duodenum, without any continuity with the inner circular layer. Costacurta (1972) and Holla (1994), however, reported continuity with both muscle coats of duodenum.

Haley & Perry (1949), Costacurta (1972) and Jit & Grewal (1977) mentioned the presence of elastic fibres in adult tissue. However, in this study of foetal tissue no elastic fibres could be demonstrated except in the walls of larger blood vessels. Presence of skeletal muscle fibres in the AM or der Hilfmuskel is an opinion shared by all those who have worked on foetal tissue.

Hollinshead (1971), Romanes (1986) and Mc Minn (1994) reported a single fibromuscular structure. In the present series however, two separate fibromuscular structures that might or might not have interconnections by fibrous tissues were demonstrated as described by Bannister (1995).

The present study shows that, in the Manipuri foetuses, the SMD and the AM are two morphologically and histologically separate entities fully formed by 36 to 40 weeks of gestation. Histologically, the AM is made up of striated muscle, whereas the SMD is composed of smooth muscle fibres that are continuous only with the outer longitudinal muscular layer of the duodenal wall. There is no interconnecting tendinous structure except some fibrous tissues devoid of any elastic fibres.

References:

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Fig.1

Photomicrograph showing smooth muscle fibers in the suspensory muscle of Duodenum. Van Geison's Stain X 200. Sf= Smooth muscle fibres, Cf = Collagen Fibres, Dw = Duodenal wall.

 

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Fig. 2

Photomicrograph of the suspensory muscle of duodenum with Duodenal wall. Masson's Trichrome stain x 200. Dw = Duodenal wall, Sf = Smooth muscle fibres, Cf = Collagen fibres.

 

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Fig. 3

Photomicrograph of elastic fibres present in the walls of blood vessels only. Voerhoff's Haematoxylin stain x 200. Ef = Elastic fibres, Cf = Collagen fibres.

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