Hypoplasia of the kidney

Renal hypoplasia is a congenital anatomical pathology, when the organ is considered normal in histological structure, but its size is far from the normal range. Apart from its abnormal size, the reduced kidney is no different from a healthy organ and is even capable of functioning within its miniature size.

[ 1 ], [ 2 ], [ 3 ]

Epidemiology

According to autopsy data, renal hypoplasia occurs in 0.09-0.16% of cases.

[ 4 ], [ 5 ], [ 6 ], [ 7 ], [ 8 ], [ 9 ], [ 10 ]

Causes renal hypoplasia

The cause of renal hypoplasia is insufficient mass of the metanephrogenic blastema with normal ingrowth and inducing effect of the metanephros duct. Therefore, all nephrons have a normal structure and are functionally competent, but their total number is 50% less than normal. In essence, this is a miniature norm. The contralateral kidney has a larger number of nephrons. Therefore, the total function is usually not affected.

It is believed that renal hypoplasia, like any other hypoplasia, is a defect of intrauterine development. Violation of intrauterine organ formation is closely related to external and internal factors affecting the body of a pregnant woman. Renal hypoplasia, the causes of which most often lie in the underdevelopment of the metanephrogenic blastema, which is the smallest nodes of specific blastema cells, can be a hereditary pathology. If the blood supply to the blastema nodules is impaired, they are unable to activate the formation of glomeruli and renal tubules, the organ cannot develop and acquire normal sizes. Renal hypoplasia can be caused by the following reasons:

• Primary underdevelopment (hypogenesis) associated with genetic predisposition.
• Pyelonephritis that develops in utero or before the age of one year.
• Secondary inflammatory process in hypoplastic kidneys, which are vulnerable in terms of inflammation of interstitial tissues.
• Intrauterine thrombosis of the renal veins, leading to underdevelopment of the organ.
• Oligohydramnios, insufficient volume of amniotic fluid.
• Anomalies in fetal position.
• Maternal infectious disease – influenza, rubella, toxoplasmosis.

Some authors, specialists in nephropathology, believe that most often the causes of renal hypoplasia are of an intrauterine inflammatory nature and are provoked by hidden pathologies in the rudiments of the glomeruli and renal pelvis.

Hypoplasia can also be provoked by external factors that affect the health of a pregnant woman, these include the following reasons:

• Ionizing radiation.
• Injuries, including abdominal contusions.
• External hyperthermia is a woman’s prolonged exposure to the scorching sun, in abnormally hot conditions.
• Alcohol abuse, chronic alcoholism.
• Smoking.

[ 11 ], [ 12 ], [ 13 ]

Pathogenesis

On pathological section, the hypoplastic kidney has the cortical and medullar layers typical of renal tissue and a narrow, thin-walled artery.

Almost half of children diagnosed with renal hypoplasia also have other anomalies – doubling of a solitary kidney (the only, relatively healthy one), eversion (exstrophy) of the urinary bladder, abnormal location of the urethra (hypospadias), narrowing of the renal artery, cryptorchidism.

[ 14 ], [ 15 ], [ 16 ], [ 17 ]

Symptoms renal hypoplasia

If the pathology is unilateral, and the solitary (the only relatively healthy) kidney functions normally, hypoplasia may not show symptoms throughout life. If the solitary kidney does not fully cope with the double function, the hypoplastic organ may become inflamed, pyelonephritis develops with a typical clinical picture characteristic of this disease. Often, the cause of persistent arterial hypertension in a child is precisely renal hypoplasia. Chronic nephropathic hypertension often leads to the need to remove the hypoplastic kidney, since the renin-dependent form of the disease does not respond to drug treatment and becomes malignant.

The pathology of organ underdevelopment can manifest itself more clearly in a clinical sense:

• The child is clearly lagging behind in physical and mental development.
• Paleness of the skin, puffiness of the face and limbs.
• Chronic diarrhea.
• Subfebrile temperature.
• Multiple signs similar to the symptoms of rickets - softening of bone tissue, characteristic protruding frontal and parietal tubercles of the skull, flat back of the head, curvature of the legs, bloating, baldness.
• Chronic renal failure.
• Arterial hypertension.
• Constant nausea, possible vomiting.

Bilateral hypoplasia has an unfavorable prognosis for children in the first year of life, since both organs are unable to function and are not subject to transplantation.

Unilateral renal hypoplasia rarely manifests itself with specific symptoms and is detected accidentally during a medical examination or comprehensive examination for a completely different disease.

Renal hypoplasia in newborns

Congenital anomalies in the formation of the genitourinary organs have, unfortunately, become increasingly common in recent years. Renal hypoplasia in newborns accounts for almost 30% of all detected congenital malformations of the fetus. Bilateral renal hypoplasia in infants is detected in the first days or months of life after birth, since neither kidney is able to function normally. The clinical signs of general renal hypoplasia are as follows:

• Developmental delay, possible absence of congenital reflexes (support reflex, protective reflex, Galant reflex, others).
• Uncontrollable vomiting.
• Diarrhea.
• Subfebrile body temperature.
• Clear signs of rickets.
• Intoxication due to poisoning by the products of one's own metabolism.

Severe bilateral renal hypoplasia in newborns is characterized by rapid development of renal failure, which often leads to the death of the infant in the first days after birth. If hypoplasia affects one to three segments of the organ, the child may be viable, but he or she develops persistent hypertension.

Unilateral hypoplasia is characterized by low concentration capacity of the viable organ, but when conducting biochemical analyses, blood indices are within normal limits. Arterial hypertension may develop at a later age, usually during puberty.

Renal hypoplasia in newborns is a congenital anomaly resulting from external or internal influence on the fetus. That is why future mothers and pregnant women need not only to learn this information, but also to do everything possible to neutralize harmful factors affecting the fetus as much as possible.

[ 18 ], [ 19 ], [ 20 ]

Renal hypoplasia in a child

Renal hypoplasia in a child aged one year or more may not manifest itself for a long time and is detected during examination for acute pyelonephritis or persistent high blood pressure. Also, prolonged pyuria (pus in the urine) or hematuria (blood in the urine) may be the basis for a comprehensive nephrological examination. Parents should be alerted by the following symptoms, possibly indicating a pathological condition of the child's kidneys:

• Dysuria is urinary retention, polyuria (excessive urination) or frequent urination with small amounts of urine.
• Painful urination.
• Enuresis.
• Convulsive syndrome.
• Changes in the color and structure of urine.
• Complaints of pain in the lower abdomen or pain in the lumbar region.
• Swelling of the face and extremities (pastosity).
• Periodic increase in blood pressure.
• Constant thirst.
• Delay in physical development, weakness.

Renal hypoplasia in a child may be clinically manifested by the following signs:

• Dryness of the skin.
• Pale, sallow skin color.
• Swelling of the face in the preorbital area (around the eyes).
• Common swelling - limbs, trunk.
• Persistent hypertension and headache.
• Pathological generalized edema – anasarca (edema of intermuscular tissue and subcutaneous tissue), characteristic of nephrotic syndrome.
• Pyuria, hematuria.
• In boys – cryptorchidism (non-descended testicle into the scrotum).

Kidney hypoplasia in a child is described in some detail by the Swedish urologist Ask-Upmark as a segmental congenital pathology of the organ, in which hypoplastic parenchymatous areas of the organ are combined with underdevelopment of the arterial renal branches. According to the Swedish doctor, such a pathology most often "starts" with clinical symptoms at the age of 4 to 12 years in the form of hypertension, changes in the vessels of the fundus visible in the study, and uncontrollable thirst (polydipsia).

A congenital anomaly is most often determined during a medical examination regarding the child’s enrollment in a kindergarten or school, and less often during an examination regarding existing diseases not related to the kidneys.

Forms

In nephrological practice, renal hypoplasia is divided into three types:

1. Simple renal hypoplasia occurs when an insufficient number of nephrons and calyces is detected in the abnormal organ.
2. Hypoplasia combined with oligonephronia (bilateral hypoplasia with a small number of nephrons, glomeruli and an increase in connective tissue, dilated tubules).
3. Renal hypoplasia with dysplasia (malformations of renal tissue – embryonic glomeruli with unformed mesenchymal tissue, often with areas of cartilaginous tissue).

Hypoplasia of the right kidney

Hypoplasia of the right kidney is practically no different from hypoplasia of the left kidney, at least in neither clinical nor functional sense are these two anomalies distinguishable. Hypoplasia of the right kidney can be diagnosed either by chance or at the intrauterine stage of fetal development or during the initial examination of a newborn baby.

Differentiation of a hypoplastic organ is difficult, since hypoplasia on echography is extremely similar to another pathology - a shrunken organ, dysplasia, which is a separate disease. An insufficient number of renal glomeruli and calyces is the only difference between an abnormal kidney and a completely healthy one, the structure and functionality of the underdeveloped organ are preserved. The insufficiency of a hypoplastic kidney is compensated by a solitary kidney, that is, the kidney that remains relatively healthy. Hypoplasia of the right kidney means some hypertrophy of the left kidney, which increases, trying to do additional work. Anatomically, the right kidney should be located slightly lower than the left, since it is in contact with a fairly large right-sided organ - the liver. It is noted that hypoplasia of the right kidney is most often found in females, which is most likely due to the anatomical features of the female body structure. Hypoplasia of the right kidney, as a rule, does not require special therapy, provided that the left kidney is functioning normally. If no physiological abnormalities are detected other than hypoplasia, there is no urinary tract infection, no nephropathy, no urinary reflux (urine reflux), no treatment is required. Of course, if hypoplasia of the right kidney is detected, the left one should be protected to prevent its disease, which can lead to aggravated complications.

Regular medical check-ups, following a gentle salt-free diet, some limitation of physical activity, avoiding hypothermia, viruses and infections are quite sufficient measures for a full, high-quality life with one functioning kidney. If a severe condition develops, accompanied by nephroptosis of a single organ, arterial hypertension or acute pyelonephritis, nephrectomy is possible.

[ 21 ], [ 22 ]

Hypoplasia of the left kidney

Anatomically, the left kidney should be located slightly higher than the right, so hypoplasia of the left kidney may manifest itself with more pronounced clinical symptoms.

Signs indicating underdevelopment of the left kidney may include aching pain in the lower back. Apart from periodic pain, hypoplasia of the left kidney, as a rule, does not present any other signs. Sometimes a person can live his entire life with a hypoplastic left kidney without even suspecting it, especially if the right kidney fully provides homeostasis, although it is hypertrophied due to the vicarious (replacement) function. It should be noted that the absence of pathological symptoms in case of organ underdevelopment is not a guarantee of safety in the future: any infection, hypothermia, trauma can provoke pyelonephritis, the formation of persistent arterial hypertension and a significant decrease in the activity of the collateral working kidney. It is believed that hypoplasia of the left kidney is most often defined as a congenital pathology in males, although there is no accurate statistical information confirmed by the international medical community.

It should be noted that hypoplasia of the left kidney, as well as underdevelopment of the right kidney, have not been studied fully enough, so there are still disagreements in the field of standards of therapy for this anatomical pathology. Hypoplasia of the left kidney, provided that the right one is functioning normally, does not require treatment. The patient only needs regular examinations, it is necessary to periodically donate blood and urine for laboratory tests and undergo an ultrasound examination.

Diagnostics renal hypoplasia

Currently, it is sufficient to conduct MRI or MSCT, if necessary - in combination with dynamic nephroscintigraphy. In clinical terms, the condition of the contralateral kidney is of great importance in this defect, since its disease or injury can lead to renal failure.

Dysplastic kidney or true renal hypoplasia is characterized by a decrease in this organ with general underdevelopment of its structure, vessels, and this type of anomaly can be bilateral. The cause of renal dysplasia is insufficient induction of the metanephros duct for differentiation of the metanephrogenic blastema after their fusion. Clinically, this kidney malformation most often manifests itself as arterial hypertension and symptoms of chronic pyelonephritis, which is associated with the abnormal structure of both the intraorgan vascular network, main vessels, and the calyceal-pelvic system. Renal failure is characteristic of the bilateral process. Differential diagnostics of dysplastic kidney is carried out with dwarf and shrunken kidney.

[ 23 ], [ 24 ], [ 25 ], [ 26 ], [ 27 ], [ 28 ]

Differential diagnosis

Differential diagnostics of renal hypoplasia is performed with renal dysplasia and shrunken kidney. Hypoplasia is evidenced by the normal structure of the renal vessels, the calyceal-pelvic system, and the ureter, which could have been previously established by excretory urography, retrograde ureteropyelography, renal angiography, and dynamic nephroscintigraphy.

Treatment renal hypoplasia

If the cause of arterial hypertension is renal dysplasia or pyelonephritis is diagnosed against the background of this anomaly, then the following treatment for renal hypoplasia is indicated - nephrectomy.

Underdevelopment of one or both kidneys is a complex pathology, due to late detection and diagnosis. Renal hypoplasia treatment involves variable treatment, depending on the type of hypoplasia and the condition of the solitary, functioning kidney.

The treatment tactics for unilateral hypoplasia are developed taking into account the individual characteristics of the patient's health. Most often, therapeutic measures are similar to the treatment of patients with one kidney.

If the collateral kidney performs the double function in full, no special treatment is required. Therapeutic actions are possible only if pyelonephritis of the hypoplastic kidney is suspected. Some specialists recommend performing nephrectomy of the underdeveloped organ, even if the collateral kidney is healthy. This is explained by the fact that the underdeveloped organ is a potentially dangerous focus in the infectious and immune sense and can affect the healthy kidney.

Also, renal hypoplasia requires treatment in the case of persistent hypertension that does not respond to standard drug therapy. Removal of a hypoplastic kidney is usually indicated for adult patients. Children whose hypoplastic kidney is capable of functioning at least at 30% of its intended volume are shown dispensary registration, observation, regular examinations and symptomatic treatment if the slightest functional deviations are suspected.

If severe bilateral renal hypoplasia is detected, treatment must be surgical, usually removing both abnormal kidneys. The patient is placed on hemodialysis and undergoes a donor kidney transplant.

Forecast

If the anomaly is determined at an early age and diagnosed as bilateral hypoplasia, attempts can be made to restore and correct the water-electrolyte balance, neutralize azotemia (intoxication of the blood with nitrogenous products). However, with severe bilateral hypoplasia, the child most often dies from uremia and heart failure (decompensation). The prognosis is usually unfavorable; children with such a severe pathology live from 8 to 15 years.

[ 29 ], [ 30 ]