854 published articles
Congenital variations are more common in men than in women (1.5-2.0:1). Variations and anomalies of the reproductive tract, however. are less common in men. Genital variations with renal agenesis are reported found in 12% of men and 40% of women.
Variations of the Lobes and Fissures of the Lungs An accessory inferior lobe is frequently found on the undersurface, extending up onto the medial surface in front of the pulmonary ligament. This lobe may be indicated by a shallow fissures or be clearly defined. It may present a tongue-like projection inward or may comprise the entire medial portion of the base, but usually consists of one-fifth to one-third of the base. The lobe may occur on either side or on both; it is larger and more frequently well-defined on the right, but more often present, or at least indicated, on the left.
A foramen is commonly found near the upper lateral angle, a little below the superior tubercle of the thyroid cartilage, which transmits the superior laryngeal artery and rarely some fibers of the external branch of the superior laryngeal nerve. The foramen represents a cleft between the fourth and fifth branchial bars. It is common for one of the superior horns to be shorter than the other, and also common for one to be absent, more frequently on the left side. The thyroid cartilage may articulate with the hyoid bone.
There may be supernumerary (two to four) puncta. Duplication of the canaliculus is rare (1:60,000). The puncta are occasionally imperforate. Diverticula of sinuses in the lacrimal duct may occur, or the nasolacrimal duct may be doubled. Reference Wolff, E. (1954) The Anatomy of the Eye and Orbit, 4th ed., Lewis, London.
According to Gutierrez, 40% of pathologic conditions of the urinary system are due to variations. Urologic variations are found in 10% of vertebral variations, in 15% of meningocele or myleomeningocele, in 25% of double anus, 42% of duplication of colon, 90% of duplication of genitalia (Cernak, 1989). The kidneys sometimes vary from their normal form, being either longer and narrower or shorter and more rounded. The characteristic fetal lobulation may persist in the adult (7%). Occasionally, one kidney is very small, while the other is proportionally enlarged.
The iris may be partially or totally absent (coloboma). In some cases, the irides differ in color (congenital heterchromia). The embryonic pupillary membrane may persist; the pupillary membrane was described by Waschendorff in 1738.
The most important variations are related to defective development and imperfect fusion of the component müllerian ducts, which are often associated with anomalies of the uterus. When these ducts fail to reach the urogenital sinus, the vagina (and often the uterus) may be absent. Vaginal agenesis was first described by Realdus Columbus in 1572. Duplication, more or less complete, follows persistence of separate or imperfectly fused müllerian ducts.
The chief anomalous conditions of the uterus are due to defective development or imperfect fusion of the müllerian ducts, which unite to form the usual organ. Arrested development of the lower part of these fetal canals accounts for the complete absence of the uterus and vagina. Depending on the extent to which failure of fusion occurs, all degrees of doubling are produced.
Apart from various locations that accompany malposition of the uterus and ovary, variations of the uterine tube usually depend on developmental faults traceable to imperfect or aberrant formation of the müllerian ducts. Retention of the fetal tortuosity, stunted development, or complete absence may involve one or both tubes. Complete doubling of the uterine tubes may occur in association with supernumerary ovaries.
Abnormalities in the sex organs of the female are, for the most part, due to developmental deviations. Anomalies of the reproductive tract are more frequent in women than men (1.5-2.0/1). Incomplete or modification of its descent from the abdomen affect the final position of the ovary. It may retain its original suprapelvic position and lie above or upon the psoas major muscle. If the female gubernaculum (ovarian ligament) fails to adhere to the uterus the ovary may follow the round ligament and pass partly or entirely through the inguinal canal into the labium majus.
The mammae frequently develop asymmetrically, the right often being larger and lower than the left. While absence of one or both mammae is very rare, with or without associated absence of the nipple, an increase in their number is relatively common occurrence. The supernumerary mammae vary in the extent to which they are developed, being represented sometimes by well-formed accessory glands (polymastia) that may become functioning organs, but more often, particularly in the male subject. Only by rudimentary nipples (polythelia) or even pigmented areas suggesting areolae.
Cases of individuals with a functional ovary and uterus (with monthly bleeding) and with a penis., testicle (with spermiogenesis), epididymis, seminal vesicle, and prostate have been reported.
The eyelids may be absent. The margin of either lid is sometimes notched or fissured. The palpebral fissure may be wider or narrower than usual, or the lids may be united by vascularized tissue. The muscles of the lid occasionally fail to develop. Supernumerary eyelids may occur.
Most of the variations in the thyroid gland are due to a partial persistence of the median or thyroglossal duct. The most obvious example of this persistence is the lobus pyramidalis. In one study, it was found in 104 of 153 cases (nearly 68%) while in another study it was found in only 24 of 60 cases (40%). It is usually attached to the isthmus on the left side of the median plane, but it may join either of the lateral lobes. It is usually connected above the hyoid bone.
The size and shape of the thymus is variable. It may be located behind the brachiocephalic vein. It occasionally contains aberrant parathyroid tissue. According to Jaretzki, III, et al., (1977) eighteen of twenty-two patients (82%) had surgically important variations in thymic anatomy in the neck, in the mediastinum, or in both. The authors provided the following table: THYMUS VARIATIONS Jaretzki, III., et al.
These glands vary considerably in size and shape: they may be pyramidal, quadrilateral, foliate, or spherical. The right gland is usually quadrilateral, the left foliate (leaf-like). In one study, the gland varied in length from 3.5 to 7.3 cm, in width from 1.5 to 4.0 cm, and in thickness from 0.3 to 1.8 cm. The right and left glands, on average, vary only slightly. One or both glands may be absent in their normal position. Accessory suprarenal glands are occasionally found, varying in size from a pinhead (1 mm) to a large pea (5 mm).
The pineal body is variable in size and is calcified in 40% of subjects over 20 years of age, but rarely in individuals under this age. Because calcium is visible on x-ray it is a significant and useful aid in diagnosis of space-occupying lesions within the skull. Choroid plexus and habenular calcification have also been useful in diagnosis of lesions of the nervous system. Calcified choroid plexus has a reported incidence of 6.1-28% in all persons over 20 years of age. Pineal calcification occurs in 33 - 76% of the white population.
The usual text description of the parathyroid glands hold true in only about 25% of cases studied; their number and location is highly variable. They may be located within the thorax embedded in thymic tissue, in the posterior mediastinum, and in the areolar tissue associated with the pericardium. In one study of 86 glands, 76 were found dorsal to the thyroid gland, one at the ventrocaudal pole and nine caudal to it.
