Communications of the median nerve in foetuses.

BACKGROUND: Communications between the median, ulnar and musculocutaneous nerves in the arm, forearm and hand were reported in adult cadaveric and electrophysiological studies. These communicant branches may lead conflicting clinical and electrodiagnostic outcomes. While there are many studies on adult patients or cadavers, there is poor regarding foetuses. The present study was conducted to examine the frequencies of these communications and their coexistences in human foetuses. MATERIALS AND METHODS: Anterior aspect of the forearms of 50 foetuses (29 females, 20 males, and 1 unknown) were dissected bilaterally (totally 100 sides) for this purpose. RESULTS: Communications between the median and the musculocutaneous nerves in the arm were found unilaterally in 4%. Communications from the median to the ulnar nerve in the forearm were encountered unilaterally in 22%, and bilaterally in 12%; from the ulnar to the median nerve in the hand unilaterally in 28%, and bilaterally in 12%. Coexistence of all these variations was not encountered in any foetus. But coexistence of two different types of communicant branch was encountered in 4%. CONCLUSIONS: Precise knowledge of nerve communications, variations and rate of coexistences in foetuses may have significance for clinicians and researchers dealing with subjects in foetal period.

Topographical anatomy of the pronator teres muscle and median nerve: a study using histological sections of human fetuses.

The median nerve passes through the humeral and ulnar heads of the pronator teres muscle (PT), although variations such as absence of the ulnar head may exist. We observed histological sections of the upper extremity from 24 embryos and fetuses. In the early stage, the PT extended between the radius and the medial epicondyle of the humerus, but no candidate for the ulnar head was found. In mid-term fetuses, the ulnar margin of the PT was attached to the elbow joint capsule. Moreover, in late-stage fetuses, a small deep part of the PT arose from the thick joint capsule of the humero-ulnar joint near the coronoid process of the ulna. This joint capsule also provided the most proximal origin of the flexor digitorum profundus muscle. Therefore, we considered fetal PT origin from the capsule as a likely candidate for the ulnar head. Consequently, the PT seemed to develop from a single anlage through which the median nerve passed, but later - possibly after birth - a small PT origin from the joint capsule appeared to obtain an aponeurosis connecting the muscle fiber to the ulna. This secondary change in PT morphology might explain the muscle variation seen in adults.

Formation of median nerve from single root on left side and communicating branch from median nerve to musculocutaneous nerve on right side.

We report here a rare variation of median nerve in an adult male cadaver observed during routine cadaveric dissection. A meticulous dissection was performed and the observations were noted. On left side, median nerve was formed from lateral cord. On right side, median nerve was formed by fusion of two slightly longer roots. The communicating branch from median nerve goes laterally to join musculocutaneous nerve. This communicating branch lies between biceps brachii and brachialis muscle and gives small branches to brachialis muscle. Knowledge of these variations is important to anatomists, radiologists, anaesthesiologists and surgeons, which may contribute to the explanation of diagnosis and surgical treatment, which can prevent any postoperative complications during surgery. The knowledge of this anatomical variation is important specially when performing plexus bloc or Latarjet's procedure.

Accessory head of flexor pollicis longus muscle in fetuses and adult cadavers and its relation to anterior interosseous nerve.

This study was conducted to examine the accessory head of flexor pollicis longus muscle (ahFPL) and its relation with the anterior interosseous nerve (AIN) in human fetuses and adult cadavers. Ninety fetus forearms and 52 adult cadaver forearms were dissected to evaluate the incidence, morphology, and innervation of the ahFPL. The ahFPL was observed in 29/90 (32%) of the fetus forearms and 20/52 (39%) of the adult cadaver forearms. The overall side incidence was 34.5% (49/142) among total forearms examined. On the other hand, the population incidence of ahFPL was 42% (19/45) in fetuses while it was 50% (12/24) in adult cadavers. So, the overall incidence in humans was 44.9% (31/69) in the population studied. Compression of the AIN in the forearm by the ahFPL is known as one of the causes of the anterior interosseous nerve syndrome (AINS). So, the relation of ahFPL with the AIN was evaluated, and in light of previous classifications a modified new classification is proposed. The most common relation detected in this study was Type IVa (71.4%) (AIN and its branches coursed posterior to the ahFPL). While Type I was not observed in this study, the incidences of Type II, Type III, and Type IVb (all AIN branches 'without AIN itself' coursed posterior to the ahFPL) were 2%, 14.3%, and 12.3%, respectively. The Types I, IVa, and IVb are thought to be associated with complete or incomplete types of AINS and Type III with incomplete type of AINS only.

Anatomical variability of median nerve formation in human foetuses in clinical aspect.

BACKGROUND: The median nerve is an important nerve leaving the brachial plexus. Median nerve damages may result from tunnel syndromes or injuries. The nerve anatomical variants are of great clinical importance in hand surgery. OBJECTIVES: Clinical evaluation of median nerve divergence from brachial plexus morphological variability in foetal period. MATERIAL AND METHODS: The material consisted of 220 brachial plexus sections derived from 110 foetuses aged 14-32 weeks of foetal life (50 females and 60 males, in CRL: 80-233 mm). The survey incorporated the following methods: dissection, anthropological, image digital acquisition, Image J computer transformation system, GIMP programme and statistical methods. Typology assessment was based on 0/1 system. Sexual dimorphism and symmetry were examined. RESULTS: Median nerve left directly lateral cord in 5 cases. In 59 (26.81%) plexuses, anterior division of middle trunk co-created median nerves anomalies. The total of 9 types of anterior division of middle trunk as well as of median nerve were distinguished. Median nerve double root leaving lateral cord was observed in 10 (9.09%) cases, whereas triple lateral root was seen in one case. In 1/3 of the examined plexuses, median nerve roots combined to form the nerve beneath humeral bone head and even in ½ of the bone distal length (type II and III). Type II prevailed more often on the left side. CONCLUSIONS: Median nerve roots as well as the median nerve itself are characteristic for significant morphological variability. Nerve roots low junction into median nerve is clinically favourable as it can prevent nerve damage during injuries.

The motor branches of median and ulnar nerves that innervate superficial flexor muscles: a study in human fetuses.

PURPOSE: We aimed to describe the distribution of the motor branches of the median and ulnar nerves that innervate the superficial flexor muscles in detail, as well as to determine any communication between these two nerves in a series of 100 human fetuses. METHODS: This study was performed on 200 upper limbs from 100 fetuses. However, the motor branches of the median nerve were determined on 50 upper limbs because of the developmental properties of medial epicondylar muscles. RESULTS: The motor branch, which innervates the pronator teres, is classified into two types and four subtypes. The flexor carpi radialis branch arose as a single branch in 30% of the cases. The innervation of the flexor digitorum superficialis was also performed by a single muscular branch in 88% of the cases and by two branches in 12% of the cases. The ulnar nerve was classified into two types according to the number of muscular branches in the forearm. Martin-Gruber anastomosis was observed in 7.5% of the cases. CONCLUSIONS: These results show differences from classical definitions regarding the muscular branching patterns of the median and ulnar nerves. We suggest revisiting the classical descriptions of innervation patterns of pronator teres, palmaris longus and flexor carpi radialis muscles, since the variations observed in their innervation patterns are more diverse than has been described.

Vagus, hypoglossal, and median nerves in human development.

In spite of the wealth of literature on the changes of the neurons in development of the brainstem and the spinal cord in vertebrates, the alterations of the cranial nerves and somatic nerves during the prenatal period was largely neglected. Particularly in humans, little information was available. The article reports the changes in the vagus, hypoglossal, and median nerves in the fetus and term babies. The changes of proportion of different-sized nerve fibers are documented. The patterns were different in the three nerves and the hypoglossal nerve seemed to show "pruning" of fibers during this period.

Observation of the relationship between the shape of skeletal muscles and their nerve distribution patterns: a transparent and microanatomic study.

BACKGROUND: There are many gaps in the understanding of the neuroanatomy of skeletal muscles with regards to the nerve distribution pattern and shape of the muscles. This study was designed to examine the entire intramuscular nerve-distribution patterns of various human skeletal muscles. METHODS: The relationships among nine skeletal muscles with various architecture (rhomboid major, biceps brachii, flexor pollicis longus, rectus femoris, sternohyoid, trapezius, masseter, digastric muscles) and their nerve-distribution patterns were investigated in four fetal cadavers using the Sihler staining method. The diameter and number of extramuscular (main) and major nerve branches, the number of minor nerve branches, and anastomoses were examined and evaluated statistically. RESULTS: With regards to the number of extramuscular (main) nerve branches, the rhomboid major muscle resembled the flexor pollicis longus, trapezius, masseter, and sternohyoid muscles, and the anterior belly of the digastricus muscle (p > 0.05), whereas it was significantly different from the rectus femoris, the posterior belly of digastricus, and the long and short heads of the biceps brachii (p < 0.05). Trapezius and masseter muscles were different from all of the skeletal muscles that were studied with regards to the diameter of main branches (p < 0.05). The masseter muscle had the largest diameter (p < 0.05). With regards to the number of minor nerve branches, the sternohyoid muscle was significantly different from all the skeletal muscles that were studied (p < 0.05) except the short head of the biceps brachii, rectus femoris, and the posterior belly of digastricus (p > 0.05). As for the number of neural anastomoses, the sternohyoid muscle was statistically different from all skeletal muscles that were studied (p < 0.05) except the masseter and trapezius muscles (p > 0.005). CONCLUSIONS: A surgeon's thorough knowledge of the relationship between the shape and nerve distribution pattern of skeletal muscles is important in successful reinnervation and regeneration of these muscles. It might also be useful in the field of muscle transplantation.

Abnormal cutaneous nerve outgrowth: a secondary effect of methyl triazene teratology in developing mouse limb buds.

The cutaneous branches originating from the superficial distal division of the ulnar nerve exhibit abnormal developmental features in 70.2% of the forelimb buds from embryos submitted 2 or 3 days earlier to methyl triazene administered to their pregnant mother. Similar abnormalities characterize the preaxial ventral cutaneous nerve of the thumb in 17.8% of forelimb primordia. The affected nerves undergo anticipated growth with respect to the normal schedule, follow abnormal pathways through areas of extensive cell death, and finally reach the apical ectoderm where they run in close contact with the basement membrane without forming a plexus. Histological observations gathered in pyronin-methyl green stained serial sections as well as in whole limb buds after cholinesterase method suggest that three factors probably contribute to modify nerve outgrowth: (1) a discrepancy between the rate of nerve progression and that of mesodermal growth in the prospective zeugopod territory which is preferentially affected by the teratogen; (2) facilitated nerve pathfinding into areas strongly hit by triazene-induced mesodermal cell death; and (3) alteration or abolition of some unknown ectodermal influence necessary to stimulate selective guidance of terminal sensory afferents and to maintain them transiently at some distance from the epidermis.

Central reorganization of sensory pathways following peripheral nerve regeneration in fetal monkeys.

Transection of a sensory nerve in adults results in profound abnormalities in sensory perception, even if the severed nerve is surgically repaired to facilitate accurate nerve regeneration. In marked contrast, fewer perceptual errors follow nerve transection and surgical repair in children. The basis for this superior recovery in children was unknown. Here we show that there is little or no topographic order in the median nerve to the hand after median nerve section and surgical repair in immature macaque monkeys. Remarkably, however, in the same animals the representation of the reinnervated hand in primary somatosensory cortex area (area 3b) is quite orderly. This indicates that there are mechanisms in the developing brain that can create cortical topography, despite disordered sensory inputs. Presumably the superior recovery of perceptual abilities after peripheral nerve transection in children depends on this restoration of somatotopy in the central sensory maps.

Outgrowing nerves in the foreleg of a mouse embryo as viewed by three-dimensional reconstruction from electron micrographs.

Electron micrographs from serial cross-sections of 12-day-old mouse forelegs were digitized and three-dimensional reconstruction of the data was carried out on an Apple Macintosh Quadra 700 computer using a program especially designed for this purpose. Two nerve endings of the palmar net of the median nerve were visualized together with their accompanying Schwann cells and the surrounding processes of fibroblasts. Naked axons invade straightly into the embryonic connective tissue and serve as contact guidance for the Schwann cells to follow. Fibroblasts with long processes extend around the axons with a parallel orientation. Contacts between axons and fibroblasts are occasionally observed. It is unclear whether the parallel orientation of nerve endings and fibroblast extensions have any biological significance.