Platybasia is an anomaly of the structure of the skull, characterized by its flatter than normal base. It may have an innate, less often acquired character. Clinically, platybasia manifests itself with extreme flattening or in combination with other craniovertebral anomalies. For diagnosis, a high-quality radiograph of the skull in a lateral projection is often sufficient, sometimes a CT scan of the skull, MRI of the brain, radiography or CT of the cervical spine is required. In the absence or mild severity of clinical symptoms, platybasia does not need treatment. Surgical intervention is possible with a combined pathology with a pronounced clinic, it boils down to an increase in the size of the large occipital foramen.
General information
The term “platybasia” was proposed in 1857 by Rudolf Virchow. Translated from Greek, “basis” is the base and “platys” is flat, which most accurately expresses the essence of the anomaly. Platybasia refers to disorders of the development of the base of the skull, among which basilar impression, deflection of the posterior cranial fossa and convexobasia are also distinguished. In turn, this group of diseases is related to craniovertebral anomalies, which also include Chiari anomaly, Atlanta assimilation, atlantoaxial dislocation. An important point for practitioners in the field of neurology is the issue of differentiation of pathology of the craniovertebral zone. In this regard, clear radiographic and tomographic criteria for each anomaly have been developed to date.
Causes
The most common is primary, or congenital, platybasia. The causes of its development include genetic determinism and various teratogenic factors: radiation, taking certain medications or contact with chemicals during pregnancy, harmful addictions of a woman (drug addiction, alcoholism, smoking during pregnancy), metabolic disorders in her body (diabetes mellitus, hypothyroidism) and infections during pregnancy (syphilis, herpes, cytomegalovirus, toxoplasmosis, rubella). Primary platybasia is noted in mucopolysaccharidosis and Down syndrome. It is often combined with basilar impression, Chiari anomaly, osteochondropathy.
Secondary platybasia has an acquired character and occurs when the structure of the bones of the skull is disturbed. For example, with rickets, osteoporosis, osteomalacia, hypothyroidism, connective tissue dysplasia, deforming osteitis. It is often accompanied by a basilar impression.
Symptoms
With mild to moderate severity, platybasia does not give clinical symptoms. Signs of neurological disorders appear only at the III degree of flattening of the base of the skull and are caused by a reduced volume of the posterior cranial fossa. Such pronounced platybasia is characterized, first of all, by symptoms of intracranial hypertension: diffuse bursting headaches, a feeling of heaviness on the eyeballs, nausea, sometimes vomiting. There may be signs of autonomic dysfunction — hyperhidrosis, hot or cold flushes, tachycardia, fluctuations in blood pressure.
In cases where platybasia is combined with basilar impression, along with diffuse headaches, pain in the occipital region is observed, which may be unilateral. Due to compression of the cerebellum, moderate symptoms of cerebellar ataxia appear. As a rule, there are dizziness, nystagmus, uncertainty when walking due to some instability and staggering. Often patients complain of paresthesia in the hands and neck. There may be symptoms of damage to IX-XII pairs of cranial nerves (dysphagia, hearing loss, voice disturbance).
Diagnostics
With the I-II degree of flattening, platybasia is often revealed as an unexpected finding of the radiologist, since it does not manifest itself clinically in any way. Fundamental in the diagnosis of platybasia is the determination on the lateral projection of the skull of the basilar Weckler angle, or sphenobasilar angle. Its peak is the center of the Turkish saddle. The sides are formed by lines running from the apex to the frontal-nasal junction (nasion) and to the anterior edge of the occipital foramen (basion). The normal value of the Vecchler angle during skull radiography is in the range of 123-152 ° When assessing this indicator by the middle sagittal section of the MRI of the brain, the normal value of the angle varies from 125 to 143 °. It is depending on the size of the sphenobasilar angle that the platybasia is divided into 3 degrees. The radiological signs of platybasia include: an increase in the angle of the Vecchler, a shortened slope, an increased angle of inclination of the occipital opening to 40-50 °, preserved pneumatization of the sphenoid sinus, a decrease in the distance between the atlas and the apex of the temporomandibular joint to 19-20 mm at a norm of 21-39 mm.
To differentiate platybasia from basilar impression, it helps to determine the position of the epistropheus (process II of the cervical vertebra) in relation to the Chamberlain line passing through the opisthion of the occipital foramen and the posterior edge of the hard palate. Platybasia is characterized by the location of the epistrophe at the level of this line, for a basilar impression, the position of the epistrophe above the Chamberlain line is typical by 6-30 mm. In difficult diagnostic cases, with combined pathology of the craniovertebral region, along with cranial radiography, it is advisable to conduct CT of the skull, MRI of the brain, radiography of the spine in the cervical spine or CT of the spine, consultations of a neurologist, geneticist, ophthalmologist, neurosurgeon.
Treatment
In cases where platybasia does not manifest clinical symptoms, it does not need therapy. If there are signs of intracranial hypertension, they are limited to treatment aimed at reducing it. Acetazolamide is prescribed with a potassium preparation, 25% magnesium sulfate, it is recommended to avoid excessive physical exertion (especially somersaults, acrobatics, horizontal bars) and limit the time spent at the computer or TV.
In cases where platybasia is combined with basilar impression and symptoms of cerebellar ataxia and lesions of cranial nerves are expressed in the clinic, the issue of surgical intervention is being considered. The operation consists in resection of a part of the occipital bone with an increase in the size of the large occipital foramen, which reduces the pressure in the posterior cranial fossa, and, consequently, compression of the cerebellum and brainstem.
Prognosis and prevention
Platybasia has a favorable prognosis for both life and recovery. It is important to take into account the presence of platybasia during manual therapy in the craniovertebral region, and in the presence of other concomitant anomalies of this zone — to adequately weigh the need for manual treatment.
Prevention of congenital platybasia consists in adequate management of pregnancy, elimination of the risk of exposure to teratogenic factors on the fetus, the use of only those medications in the treatment of a pregnant woman that do not have a similar effect. Prevention of secondary platybasia is reduced to the prevention of rickets, osteomalacia and other diseases that occur with changes in the structure of bone tissue.
