1. Clinical data and methods
1.1 General data: 15 males and 13 females out of 28 cases. The average age was 48.5 years (16 to 64 years), and the duration of the disease ranged from 5 months to 18 years, with an average of 9.6 years.
1.2 Clinical manifestations: 27 cases with headache (18 cases with headache as the main symptom), 18 cases with numbness of both upper limbs, 8 cases with walking instability and muscle weakness, 3 cases with urinary and bowel disorders, and 3 cases with head trauma and subarachnoid hemorrhage.
1.3 Imaging examination
All patients underwent head and neck mri and craniocervical x-ray examination, including craniocervical junction x-ray plain film: skull base was found to be stuck and combined with atlanto-occipital fusion in 4 cases, and the skull base measurement showed that the dentate prominence exceeded the palato-occipital line and the basal line by 7 mm; head and neck mri: the cerebellar tonsils were herniated downward into the occipital foramen, and moderate hydrocephalus was found on the screen. There were 20 cases with cervical spinal cord cavity.
1.4 Surgical method
The patients were divided into two groups according to their clinical manifestations. a group of 18 cases: acm first, hydrocephalus second. The posterior cranial fossa decompression and occipital poolplasty were performed, the herniated cerebellar tonsils were removed, the median foramen of the fourth ventricle was explored and the adhesions were separated, and the cerebrospinal fluid circulation pathway was opened. b Group 10 cases: hydrocephalus was first and acm was second. The surgical approach is to first perform a cerebrospinal fluid shunt to lower the intracranial pressure. If the symptoms of medullary compression still could not be relieved, then posterior cranial fossa decompression and occipital pooloplasty should be considered.
2.Results
2.1 Surgical results
Group a: 15 cases had obvious improvement of symptoms after surgery, 3 cases had no relief of symptoms, and cerebrospinal fluid shunt was performed again. In 8 cases, the symptoms improved significantly after surgery, and 2 cases underwent occipital saphenoplasty again.
2.2 Follow-up results
Twenty-two of the 28 patients in this group were followed up, including 14 cases in group a and 8 cases in group b. The average follow-up time was 35 months. The average follow-up time was 35 months. 22 patients had good healing and no recurrence; 12 cases showed significant reduction of spinal cord cavity on review of head and neck mri.
3. Discussion
It is not uncommon to find combined hydrocephalus in patients with subungual herniation malformation of the cerebellum [1]. However, two cases should be distinguished according to their pathogenesis. In the first case, subcerebellar tonsillar herniation comes first and hydrocephalus comes second. That is, hydrocephalus is caused by the cause of subcerebellar tonsillar herniation. The patient’s primary disease is a subcerebellar tonsillar herniation malformation, and the herniated cerebellar tonsils compress the medulla oblongata and cause adhesions, resulting in occlusion of the cerebellar medullary pool and obstruction of normal cerebrospinal fluid circulation, causing obstructive hydrocephalus. In this case, the herniation of the inferior cerebellar tonsils is the “cause” and hydrocephalus is the “effect”. In the second case, hydrocephalus comes first and submicrocephalic tonsillar herniation comes second. The patient’s primary disease is hydrocephalus, and the chronic increase of intracranial pressure due to long-term hydrocephalus causes the cerebellar tonsil tissue in the posterior cranial fossa to herniate into the upper cervical spinal canal through the foramen magnum, forming a subcerebellar tonsil herniation malformation. In this way, hydrocephalus in turn becomes the cause of subcerebellar tonsillar herniation malformation (acm).
In clinical practice, it is sometimes difficult to distinguish which of the two conditions is present in some patients with subcerebellar herniation malformation combined with hydrocephalus. The following points can be of great help in correctly determining the etiology.
(1) Subcerebellar tonsillar herniation malformation first, followed by hydrocephalus. The symptoms of increased intracranial pressure appear late in the medical history, and often the symptoms of increased intracranial pressure appear only after a long period of time after the symptoms of medulla oblongata compression have appeared.
The clinical manifestations of hydrocephalus and intracranial pressure increase are not obvious, while the symptoms caused by acm (such as medullary compression and posterior group cranial nerve symptoms) are prominent. Patients are often accompanied by narrowing of the posterior cranial fossa. In recent years, many scholars have suggested that congenital developmental abnormalities resulting in a narrow posterior cranial fossa are an important cause of submicrocephalic tonsillar herniation malformations. In addition to acm, patients are often combined with other craniocervical junction malformations: flattened skull base, sunken skull base, atlanto-occipital fusion, etc.
(2) Hydrocephalus first and then the subungual herniation malformation of the cerebellum. The history of hydrocephalus is often found to be caused by intracranial infection, subarachnoid hemorrhage, traumatic brain injury or history of cerebral parasites. Patients have prolonged symptoms of increased intracranial pressure, with early and prominent signs and symptoms of high cranial pressure (e.g., headache, nausea, vomiting, optic papilloedema, etc.) and milder symptoms due to subhypophyseal herniation of the cerebellum. Patients generally do not have abnormal development of the posterior cranial fossa and have normal posterior cranial fossa volumes or supratentorial/inferior volume ratios. No other craniocervical junction anomalies are usually combined.
Two different causal causes of subungual herniation malformation of the cerebellum combined with hydrocephalus should be treated surgically with different procedures. In the first case, i.e., patients with hydrocephalus secondary to acm, the treatment focuses on the submicrocephalic herniation malformation, and the principles of treatment are posterior cranial fossa decompression, resection of the herniated cerebellar tonsils, exploration of the median foramen of the fourth ventricle and separation of adhesions, and the opening of the cerebrospinal fluid circulation.
In this way, the secondary hydrocephalus will be relieved. If the cerebellar tonsils are herniated for a long time and the adhesions are heavy, and the normal cerebrospinal fluid circulation cannot be restored after decompressive adhesions separation in the posterior cranial fossa, a shunt operation to reconstruct the cerebrospinal fluid circulation pathway can be considered again. In the second case, since hydrocephalus is the root cause of subcerebellar herniation malformation, blindly taking posterior cranial fossa decompression and subherniation cerebellar tonsillectomy surgery cannot solve the problem of hydrocephalus. The correct approach should be to first perform cerebrospinal fluid shunt surgery to lower the intracranial pressure [2]. In this way, most patients’ symptoms can be relieved. If the symptoms of medullary compression are not relieved after a period of observation (usually 3 months), posterior cranial fossa enlargement should be considered.