ANTIBIOTICS

Antibiotics are the medicines which are used to treat infections. Infections may be due to bacteria, fungi or virsuses. Almost everyone suffers from infection someimes in his life time.

Being infected is a bad feeling and everybody dislikes it. Sometimes, these infections are so dreaded that it is better to get immunity against such bad infections. So, vaccines are used to present such bad infections, Commonly used vaccines are BCG ( to prevent Tuberculosis), DPT ( to prevent Diphtheria, Pertusis and Tetanus), Anti Hepatitis B Surface antigen Vaccine ( to prevent infection against hepatitis B), Polio vaccine, etc.

But, all infections are not so dangerous, like common cold, sore throat, and small furuncle or small reddish pimple. Such infections usually subside by themselves due to the immunity of our own body. This immunity is mainly provided by white blood cells (WBCs) and lymphocytes present in our body. These act like Policemen patrolling our internal security. These security personnel detect and kill the foreign microbials or microorgaisms like bacteria.

Sometimes, infecions may overwhelming and required to be treated with antibiotics. Like common cold not subsiding and persisting for longer duration with superadded bacterial infection or sinusitis. Or, sore throat associated with yellowish sputum with cough and fever. So, we need to take antibiotics to treat such infections.

Infections may be superficial or deep, local or systemic. The infection depends upon virulence or the microorganism, resistance of the person, and living conditions. Like persons with diabetes with uncontrolled blood sugar level and patients on long term steroids have low resistance or immunity against the infecive microrgansms. Person living in crowded places with other people infected with communicable diseases are prone to acquire infections of the airborne diseases like tuberculosis, influenza, etc.

Skin infections are commonly caused by Staphylococcus aureus and Streptococcus. Invention  of Penicillins in 1928 by Scottish researcher, Alexander Flemming, made a great difference to the outcome of patients with infecions.

Sir Alexander Fleming

Sir Alexander Fleming was a Scottish physician, microbiologist, and pharmacologist. His best-known discoveries are the enzyme lysozyme in 1923 and the world's first antibiotic substance benzylpenicillin from the mould Penicillium notatum in 1928. The simple discovery and use of the antibiotic agent has saved millions of lives, and earned Fleming – together with Howard Florey and Ernst Chain, who devised methods for the large-scale isolation and production of penicillin – the 1945 Nobel Prize in Physiology/Medicine.

Penicillin was effective against fatal infections caused by bacteria. But, over time, these bacteria outsmarted the drug and developed resistance to these drugs. But, consistent efforts by the physicians, microbiologists, pharmacologists, biotechnologists and other inventors led to the development of many anti-microbial drugs which are commonly known as antibiotics.

So, commonly uses antibiotics are penicillins, cephalosporins, tetracyclines, macrolides, quinolones, anti-viral drugs, anti-fungal drugs, etc.

Common bacteria are described as Gram positive or Gram- negative. Gram positive bacteria are stained positively by Gram stain. 

Some bacteria produce exotoxins and some produce endotoxins. 

Tbe bacteria which produce exotoxins are Cornyebacterium diphtheriae, Clostridium tetani, C.botulinum, C.perfringens, Bacillus anthracis, Staphylococcus aureus, Streptococcus pogens ( all are examples of Gram positive bacteria).

Gram negative bugs which produce exotoxins are E.coli, Vibrio cholerae, and Bordetella pertusis. 

Endotoxin is a polysaccharide and is found in the cell wall of Gram-negative bacteria. 

Some bacteria do not stain well with Gram-stain, like Treponema, Rickettsia, Mycoplasma, Legionella pneuophila, Mycobacteria and Chlamydia.

For treponemes-darkfield microscopy and fluorescent antibody staining is used. 

Mycobacteria are acid-fast bacilli. Legionella is stained with silver stain.

Gram positive bacteria are broadly classified in 2 groups; Cocci and Bacilli.

Gram positive cocci are classified into two; catalase positive clusters ( Staphylococcus) and catalase negative chains ( Streptococcus). 

Catalase postive staphylococci are further classified into two groups as Coagulase positive ( S.aureus) and coagulase negative [ Staphylococcus epidermidis ( Novobiocin sensitive) and Staphylococcus saprophyticus ( Novobiocin resistant ].

Gram postive and catalase negative chains of cocci are Strptococcus. On the basis of hemolysis Streptococci are divided into 3 categories: Green ( partial ) hemolysis; Sterptococcus pneumoniae, Clear hemolysis Streptococcus pyogens ( group A Bacitracin sensitive), S.agalactiae ( group B, Bacitracin resistant) and 3rd category of streptococci with no hemolysis examples are Enterococcus ( E.fecalis) and Peptostreptococcus( anaerobe).

Exapmple of Gram positive bacilli ( rods) are: Clostridium ( anaerobe), Cornyebacterium, Listeria and Bacillus.

Gram negative bacteria which appear pink are broadly classified into three groups : Cocci, C0ccoid rods and rods. 

Gram negative cocci are Neisseria mningitidis and N.gonorrhoeae. These two are differentiated on the basis of Maltose fermenter chacteristic. N. menigitidis is Malose fermenter and N. gonorrhoeae is Maltose noferenter.

The examples of cgram negative coccoid rods are Hemophlus influenzae, Pasteurella, Brucella and Bordetella pertusis.

Gram negative rods are further subdivided into two subtypes based Lactose fermenter characteristic. Lactose fermenter gram negative rods are Klebsiella, E,coli and Enterobacter which are Fast fermenter and Citrobacter, and Serratia Slow fermenters.

Lactose nonfermenter gram negative rods are subdivided into two groups, based on oxidase property. Oxidase positive are Pseudomonas and oxidase negative are Shigella, Salmonella and Proteus.

Penicillin C is for intravenous use and Penicillin V is for oral use. 

Penicillin binds penicillin-binding proreins , blocks transpeptidase cross-linking of cell wall and activates autolytic enzymes. It is bactericidal for gram positive cocci and rods, gram negative cocci and spirochetes.

Methicillin, nafcillin have narrow spectrum and used against penicillase resistant Staphyloccus aureus.

Ampicillin, Amoxicillin have wider spectrum, penicillanse sensitive, also combined with clavulanic acid ( penicillanase inhibitor) to enhance spectrum. Amoxicillin has greater oral bioavailability than ampicillin. These two extended-spectrum penicillin and are useful against certain gram positive bacteria and gram negative rods ( Hemophilus influenzae, E.coli, Listeria monocytogens, Proteus mirabilis, Salmonella and enterococci). 

Carbenicillin, Piperacillin and Ticarcillin are extended spectrum penicillin and useful against Pseudomonas  and gram negative rods , susceptible to penicillanase, used with clavulanic acid.

Cephalosporins are beta lactam drugs. It inhibits cell wall synthesis 

Imipenem

      Imipenem is a broad spectrum, beta lactamase-resistant carbapenem. It is always administered with cilastatin which is inhibitor of renal dihydropeptidase 1 to decrease inactivation in renal tubules. Ii is used against gram positive cocci, gram negative rods and anaerobes. It is drug of hoice against Enterobacter. Its toxicity includes GI distress, skin rash, and CNS oxicity ( seizures).

Vancomycin

Aminoglycosides

Tetracyclines 

Macrolides

Chloramphenicol

Clindamycin

Sulfonamides

Trimethoprim

Fluroquinolones

Metronidazole

References: 

Wikpedia

Alexander Fleming (1881–1955): Discoverer of penicillin, Siang Yong Tan, Yvonne Tatsumura

Singapore Med J. 2015 Jul; 56(7): 366–367. doi: 10.11622/smedj.2015105

Intramedullary spinal cord Tumors

Intramedullary tumors are the tumors which are present in the spinal cord, i.e., inside the pial covering and substance of the spinal cord itself.

This diagram explains the location of the intramedullay tumors. Piamater is the innermost of three meninges ( Duramater, Arachnoid and Piamater). It covers the spinal cord. So the tumors outside of it may be IDEM ( intradural extramedullary) or extradural lesions. 

Spinal tumors are are classified as

 (1) extradural,

(2) intradural extramedullary, and

 (3) intradural intramedullary.

Extradural tumors are the most common spinal tumors and are usually of metastatic origin. 

Intradural Extramedullary (IDEM) tumors are mainly neurofibroma and meningioma.

Intradural intramedullary lesions comprise 20 to 30% of all primary spinal cord tumors.

Gliomas make up 80% of all intramedullary tumors. The gliomas are further subdivided into astrocytomas (60 to 70%) and ependymomas (30 to 40%). Hemangioblastomas are the third most frequent intramedullary spinal cord (IMSC) tumors, comprising 2 to 15% of all intramedullary tumors. Metastatic intramedullary tumors are rare but present in 2% of all intramedullary tumors. Lipomas are commonly associated with spinal dysraphism.

Intramedullary tumors constitute about 35-40% of all intraspinal tumors in children. In children intramedullary tumors are mainly developmental in origin, like dermoid, lipoma and epidermoid). In adults intramedullary tumors may arise later in life, like astrocytoma, ependymoma and hemangioblastoma.

Gliomatous and nongliomatous tumors constitute 90 and 10% respectively.

In 75% cases, the astrocytmas extend over 4 or less 4 vertebral segments. In some cases the lesions extends throughout the spinal cord, for example holocord astrocytomas.

Half of the central nervous system ependymomas are located in the spinal cord and, of these, 50% are located in the filum terminale. The next common site is the cervical cord.

Glioblastomas are not common.

Hemangioblastoms are rare, consist of less than 2% of primary spinal cord tumors.

Clinical presentation depends upon the site and size of the lesion.

MRI of spine with contrast is the investigation of choice.

                                  Intraoperative image of my adult patient where tumor is seen after posterior midline myelotomy. Histopathology of the tumor was suggestive of Pilocytic astrocytoma ( WHO grade 1 tumor)

The operating microscope, bipolar coagulators, intraoperative physiological monitoring ( somatosensory evoked potenial monitoring, motor evoked potential ) , microscissors, microdissectors, small tumor holding forceps, Cavitron Ultrasonic Surgical Aspirators (CUSA) , intraoperative USG ( Ultrasonography) are good for safe excision of intramedullary lesions.

References

Samartzis D, Gillis CC, Shih P, O'Toole JE, Fessler RG. Intramedullary Spinal Cord Tumors: Part I-Epidemiology, Pathophysiology, and Diagnosis. Global Spine J. 2015;5(5):425-35. And references as numbered below

Mechtler L L, Nandigam K. Spinal cord tumors: new views and future directions. Neurol Clin. 2013;31(1):241–268.

Grimm S, Chamberlain M C. Adult primary spinal cord tumors. Expert Rev Neurother. 2009;9(10):1487–1495.

DeSousa A L, Kalsbeck J E, Mealey J Jr, Campbell R L, Hockey A. Intraspinal tumors in children. A review of 81 cases. J Neurosurg. 1979;51(4):437–445.

Mandigo C E, Ogden A T, Angevine P D, McCormick P C. Operative management of spinal hemangioblastoma. Neurosurgery. 2009;65(6):1166–1177.

Ravi Ramamurthy. Spinal Intramedullary Tumours. Chapter 130, Volume 2, in Textbook of Operative Neurosurgery, B.I Publications Tvt Ltd, New Delhi, Pages1107-1113.

Surgical cases of Tuberculosis of Central Nervous System

Tubercuolosis (TB) continues to be a major public health concern, especially in developing countries. TB is one of the top 10 causes of death worldwide . In 2016, 10.4 million people fell ill with TB; and 1.7 million died from the disease. In 2016, an estimated 1 million children became ill with TB and 250,000 children died of TB. 
Tuberculosis of central nervous system (CNS) can be treated effectively with anti-tubercular therapy (ATT). ATT duration for treatment of CNS TB is 12 months ( 2 months intensive phase and 10 months continuation phase). Some cases of CNS TB require neurosurgical intervention. I am presenting 3 cases of cranial TB where the presentations were unusual leading to delay in the diagnosis. All these three cases were effectively treated with neurosurgery along with ATT.

Patient 1 was a middle aged female with history of headace of long duration. CT scan of head revealed extradural collection beneath the frontal bone. The frontal bone was thickened. This was unusual as duration of symptom was in years and the bone above the lesion was thickened.

 Surgical image showing  pus coming out of frontal bone bur hole

As intensity of the headadche increased , patient was advised surgery. On craniectomy about 60 ml of pus came out under pressure. Patient became asymptomatic after surgery and ATT.

Patient 2 was a middle aged male with history of trauma and swelling over the vertex of skull about 15 days back. Patient was suspected to have scalp hematoma and swelling and was advised antibiotics and analgesics. CT scan showed a scalp swelling over the cranium. Patient underwent surgery and about 40 mL of pus was drained and it was sent for culture/ sensititivity, Gram stain , AFB stain. It came out positive for Staphylococcus. But, despite of prescribing antibiotic according to sensitivity, wound was not healing. Later, wound was re-explored and remaining pus drained out and bony osteomyelitis of the cranium was evident. Craniectomy of the pariental bone at the vertex was done and sent for histopathological examination. Biopsy was suggestive of tuberculosis.

                                                  Surgical image of the patient showing calvarial osteomyelitis

Patient's surgical wound healed with antibiotic and ATT. He became asymtomatic after taking ATT.

Patient 3 was a child of about 14 year age. He presented in emergency of my Institute with history of headache, vomiting, deterioration of conscious level, weakness of right half of body and recurrent seizures. CT scan of the brain and MRI of brain with contrast revealed intracranial subdural hypodense collections in interhemispheric fissure and left fronto-parietal convexity of brain.

                         Surgical image showing burr hole in the frontal bone and pus coming out of subdural space
Frontal region incision was made and single burr hole made in frontal bone under general anesthesisa. Dura was coagulated and incision made in dura. About 80 mL of thick pus came out under pressure. Patient improved after surgery and ATT.

Many types of neurotuberculosis have been described; most common intracranial forms are tuberculous meningitis and tuberculomas.Tuberculous brain abscess and subdural empyema are extremely rare manifestations of central nervous system tuberculosis. Subdural empyema or collection of pus in the subdural space is mostly pyogenic.  Intracranial tubercular subdural empyema is very rare in pediatric population. Various  diagnostic  modalities  and  treatment options  are  available  for  managing central nervous system tuberculosis (CNS  TB).   But, outcome  remains of CNS TB is poor as clinicians  face  many challenges  in  the  management  of  the  tubercular infection  of  the  brain  and  spinal cord.

Treatment of CNS TB is challenging due to lack of specific biochemical tests and inability to get the pathological sample from deeply located eloquent areas of CNS without causing any neurological deficit. Moreover, it is unnecessary to operate for biopsy in a patient who has presented with a very small granulomatious lesion in brain or spinal cord. In such as situations neuro-radiology helps in managing CNS TB and it may be the only source of establishing diagnosis and evaluating treatment response. Role of radiological investigation has expanded from the initial diagnosis to the therapeutic interventions. In some Muli-drug- resistant (MDR) CNS TB cases, stereotaxy or Ultrasonogram (USG) or CT guided biopsy helps in obtaining pathological sample and drug sensitivity testing. A regular clinical and neuro-radiological follow-up is mandatory during the entire course of anti tuberculous therapy to take prompt decisions to change ATT and to reduce morbidity and mortality associated with CNS TB.

Traditionally, culture for the mycobacterium is considered as gold standard for diagnosis of TB. But,  tuberculin  test,  biochemical  investigations and  AFB  stain  and  culture  of  the  cerebrospinal fluid  or  granulation  tissue  provide  little  support for the management of CNS TB or its sequelae.  There should be high index of suspicion for the CNS TB in a patient who is from an endemic region. There may be extensive tubercular involvement of CNS even  in  absence  of  the  history of pulmonary diseases,  tubercular  contact  or  any  other neurological  deficit.  It is difficult  to assess  the therapeutic response in the early follow up period in view of the lack of sensitive and specific tests. Vigilant clinical observation and imaging studies is required in the early follow up period to identify the  worsening  or  new  emerging  signs  in  the patients  of  CNS  TB.  Imaging  studies  are becoming  the  major  decisive  tools  for  the empirical  therapy  and  early  follow  up  of  the patients to evaluate the therapy.

Intracranial tubercular subdural empyema can be effectively treated with ATT and burr hole evacuation of pus. Close clinical observation, neuroradiological assessment with CT scan or MRI and prompt therapeutic interventions   are  necessary  for starting the empirical anti-tuberculous  therapy and early follow up of the patients to evaluate the therapeutic response. 

 In all these cases pus was negative for Acid Fast Bacillus (AFB). This is very common observation. So, high index of suspicion and close follow up is required in suspected cases of cranial TB. Clinical observation with empirical ATT is key in the management of CNS TB cases.

References

1.       An unusual presentation of neurotuberculosis: subdural empyema . Case report. Cayli SR, Onal C, Kocak A, Onmus SH, Tekinen A. J Neurosurg 2001 Jun; 94(6): 988-91

2.       Global tuberculosis report 2017, WHO ( www.who.int)

3.       Pediatric intracranial subdural empyema caused by Mycobacterium tuberculosis- a case report and review of literature. Banerjee AD, Pandey P, Ambekar S, Chandramouli BA. Child Nerv System. 2010, Aug: 26(8): 117-20.doi 10.1007/s00381-010-1157-3 Epub 2010 May 2

4.       Intracranial tuberculous subdural empyema: case report. Van Dellen A, Nadvi  SS, Nathoo N, Ramdial PK. Neurosurgery 1998, Aug; 43(2), 370-3.

5.        Vijaykumar B, Sarin K, Girija Mohan. Tuberculous brain abscess and subdural empyema in an immunocompetent child: Significance of AFB staining in aspirated pus. Ann Indian Acad Neurol. 2012, Apr-Jun, 15(2):130-133.

6.       Gautam VKS, Khurana S & Singh R. Diagnostic and therapeutic challenges in the surgical management of CNS tuberculosis. International Journal of Medicine and Health Sciences, 2013, Vol-2;Issue-2, 161-169. 

Concussion

Concussion means transient loss of consciousness due to head injury.
Concussion is also known as Mild Traumatic Brain Injury (MTBI). 
It may be described as alteration of consciousness without structural damage as a result of head trauma. 

It is transient loss of consciousness or alteration in mental status like alteration in conscious level,  disturbance of vision or balance due to head injury.

Trauma to the head may cause sudden linear or rotational movement of the brain.  This sudden acceleration and deacceleration  movements of the brain and brain stem disrupts the normal cellular activities in the brain ( including fornix, corpus callosum, temporal lobe, frontal lobe) and in the the reticular activating system of the midbrain.  

Although, concussion is considered as mild head injury but sometimes it has sequelae. Headache, confusion, amnesia, blurring of vision, dizziness, fatigue  may persist for some time.  More alarming long term sequelae are the cognitive impairment, sleeplessness, difficulty in concentration,  irritability, anger, behavioural abnormalities, or maladjustment in the work or studies.

Plain CT scan of brain is the investigation of choice. It is normal in cases of concussion because it is a physiological impairment and so, no anatomical abnormality is seen on non-contrast CT scan of the brain. MRI of the brain is not required and  is unnecessary. MRI will demonstrate abnormalities in up to 25% of cases where CT is normal. But, I do not suggest MRI in cases of concussion because CT actually guides the treatment. So, if CT is normal there is nothing serious and no active neurosurgical treatment is required. MRI just adds to the apprehension of the patients and their relatives and it does not provide any additional information of any use to the neurosurgeon.

Symptoms usually resolve in approximately two weeks. But, symptoms may persist for longer period.

Every person with post traumatic concussion requires emotional support. 
Patient’s caregivers, family members, teachers and co-workers and colleagues must understand that some symptoms like irritability, headache, dizziness may be sequelae of concussion.  So,  a sympathetic and considerate attitude should be adopted towards the person who had suffered mild head injury with concussion and is experiencing long term sequelae of mild head injury. 
Symptomatic treatment of like dizziness may be trated with Betahistine or Cinnarazine. Headache is a common complaint and requires both medical and psychological support.
Neurotrophic vitamins like vitamin B complex, Methylcobalamin,  vitamin E are useful.  Anxiety, sleeplessness are very well managed with tablet Clonazepam 0.25 mg at night and Psychological support.

Spina Bifida, Spinal Dysraphism, Myelomeningocele and Meningocele

Spinal dysraphism means a spectrum of congenital anomalies of the spine and spinal cord.

Spina bifida is a common form of spinal dysraphism. The term spina bifida includes a wide variety of anomalies.
  
Congenital defect in the spine leads to spina bifida. This can be of two types: spina bifida occulta and spina bifida aperta.

In spina bifida aperta; visible lesion, like a swelling over the midline of the back may be noticed at the time of birth of a child. Such spinal dysraphism is known as Spinal Bifida Aperta.

But, a child may be having some abnormalty of the spine or spinal cord but without any externally visible lesion and overlying skin is intact, then it is known as Spina Bifida Occulta.  This defect of the vertebrae of the spine of a child may not be visible at the time of birth and there may be no visible exposure of meninges or neural tissue. And, there may be congenital defect only in the lamina of the vertebrae of the spine without any involvement of underlying spinal cord. This is known as spine bifida occulta.

But, in spina bifida aperta there is a visible or open defect in the spine. There may be congenital defect in vertebral arches with cystic distension of meninges which is filled with CSF and is known as Meningocele. If, in this congenital defect of the vertebral arches there is a cystic dilatation of meninges and cerebrospinal fluid along with neural tissue or spinal cord ( Myelon) , then it is known as Myelomeningocele. If Myelomengocele contains fat tissue, then it is known as Lipomyelomengocele.

Myelmeningocele is one of the congenital open neral tube defect present at the birth on the back of the newborn.

It is a common type of congental defect of the spine and its incidence is about 1 in 1,000 live births. Better nutrition and folic acid suplementatiion during the antenatal care of the mother decrease its occurrence.

Ultrasound study during the early antenatal care detects any occurrence of myelomeningocele in a fetus during pregnancy.

A newborn child should be assessed for any sensory or motor deficit due to meningocele or myelomeningocele. There may be associated congenital lesions, like cardiac lesions. Myelomeningocele may be associated with congenital hydrocephalus. So, MRI of the spinal cord and brain is investigation for choice for assessing a case of meningcele. MRI may show whether a swelling on the back of a child is only flled with CSF or does it contain any neural tissue. It detects any intraspinal extension, associated intrasinal dermoid, lipoma, dermal sinus, spina bifida, spinal dysrahism like duplication of the cord, any bony spur between the duplicated cord, Chiari malfomation, syrinx, hydrocephalus, thickened filum terminale, etc. So, MRI helps in diagnosis, surgical planning and predicting prognostic outcome.
.

   

Arachnoid cysts, Ependymal cysts, Benign intracranial developmental cysts

Intracranial Benign Developmental Cysts

Arahnoid cysts and Ependymal cysts

It is very common observation in brain imaging to find small cysts inside the brain. These cystic areas resemble and look like areas of the brain with normal cerebrospinal fluid. Such incidental finding increase anxiety in the person in whom brain imaging was usually  done for some other purpose. Such cysts are usually arachnoid cysts or ependymal cysts.

Arachnoid Cysts

Arachnoid cyst is a benign intracranial developmental cyst which is between two split layers of arachnoid and it usually contains clear colurless CSF.

So, arachnoid cyst is a cyst containing CSF and it forms due to splitting of the archnoid membrane. These are benign congenital malformation.

It is usually an incidental finding.

They are commonly seen in Sylvian fissure, cerebellopontine angle, supracollicular area, vermian area, sellar and suprasellar area, etc. This may appear at any age from infancy and adolescence to adults.

Arachnoid cyst may remain asymptomatic throughout life, only to be diagnosed incidentally by a neuroimaging study. Imaging often shows remodelling of bone, and imaging characteristics exactly mimic CSF on CT and MRI in most cases.

Symptoms and signs of arachnoid cyst depend on its size and location inside the brain and spinal cord.

Recommendation for incidentally discovered arachnoid cyst in adults: a single follow up imaging study in 6-8 months is usually adequate to rule-out any increase in size. Subsequent studies only if concerning symptoms develop.

Sylvian fissure archnoid cyst may present with headache, seizures, dysarthria (speech problem),  focal bulge in temporal region, exophthalmos, papilloedema, and hemiparesis.  X-ray skull or CT scan may show evidence of expansion of the middle cranial fossa, elevation of the lesser wing of the sphenoid, forward protrusion of the greater wing the sphenoid bone and outward expansion and thinning of the temporal bone. But expansion of skull in relation to arachnoid cyst is not an indication for surgery , but mass effect, displacement of midline structures and presence of obsructive hydrocephalus are indications for surgical intervention for middle fossa arachnoid cysts.

On CT, arachnoid cyst appear as low density, smooth bordered lesions having attenuation values similar to that of CSF. The cyst wall has well-defined margins and does not enhance after intravenous injection of contrast agent.

MRI is better at demonstrating multiplanar relationship and characteristics of the lesion on T1, T2, FLAIR, Diffusion weighted images and contrast, MTR ( Magnetization transfer ratio), MRS ( MR spectroscopy), MRA ( MR angiography)study. It helps in differentiating arachnoid cyst from epidermoid, dermoid, lipoma, ependymal cysts, tumors like low grade glioma & metastasis, old hemorrhage, cavernoma, hydatid cyst, hemangioma, and infective granulomas.

On T1 weighted image arachnoid cyst appears hypointense and on T2 weighted image it appears hyperintense like CSF. On T1 weighted MRI ,  lipomas will appear hyperintense as fat appears hyperintense on both T1 and T2 weighted images.

The high protein content of a nonhemorrhagic tumour cyst will cause the cyst to appearslightly hyperintense to CSF on proton density images. The associated peritumoural oedema of cystic astrocytoma will look hyperintense on FLAIR image of MRI.

Ependymal cysts and epidermoid tumors appear isointense or slightly hyperintense to CSF on proton-density images. Epidermoid tumors are more likely to be lobulated, have less distinct margins, and encase rather than displace neighbouring structures. Diffusion-weighted imaging reflects the amount of Brownian motion of proteins which is greater in cystic than in solid lesions.

Sylvian fissure is the most common site for intracranial arachnoid cysts. Sylvian fissure arachnoid cyst may be of three types. It may be a small lenticular lesion at the anterior pole of the middle cranial fossa without any mass effect (Type 1) or quadrangular in shape reflecting a completely open insula (Type II) .  Type III sylvian fissure arachnoid cyst presents as large rounded area with significant compression of the brain. Displacement of the midline structures in type III cysts is an indication for surgical decompression.

Treatment of archnoid cyst

Adults with asymptomatic arachnoid cyst should be treated conservatively, even for large cysts without symptoms and signs or with only a complaint of headache. Only arachchnoid cysts which cause a mass effect or neurological deficit should be treated surgically.

In children, decompression of sylvian fissure archnoid cyst is more likely to lead to decreased parenchymal compression, cyst collapse, and subsequent resolution if intracranial hypertension and neurological deficits.

Ventriculoperitoneal shunting

Cystoperitoneal shunting

Cyst fenestration

Cyst excision

Skull may be very thin and may be even eggshell-like, so care must be taken in placing burrhole during surgery. The dura is bluish because of presence a large pool of fluid underneath. The exposed cyst wall may be clear and transparent; in some  areas  a web of milky thickening may be noted as a result of collagen reinforcement. The forntal lobe appears widely separated from the temporal lobe because of the failure of opercula to develop. So, the insula and branches of middle cerebral artery may be completely exposed after excision of the sylvian fissure arachnoid cyst. When the outer wall of the cyst is excised, clear CSF escapes. Long bridging veins may be observed either on the surface of the cyst or within the cyst. Bridging veins that traverse the cavity of the cyst do not have much support. Rupture of such unsupported veins account for high incidence of subdural hematoma associated with these cysts.

Fenestration of deep wall of cyst creates a communication between the sylvian fissure cyst and the chiasmatic cistern.

A significant number of middle cranial fossa arachnoid cysts are associated with bleeding hematomas which are usually venous in nature and result from tearing of bridging veins within or external to the cyst.  It may precipitate symptoms in a previously asymptomatic patient.

Arachnoid cyst in sella turcica

Sella turcica arachnoid cyst may be intrasellar or suprasellar. Suprasellar cysts are by far the more common. It may present with hydrocephalus, visual impairment, endocrine dysfunction ( hypopituitarism, stunted growth, etc), gait disturbance. A curious head nodding motion described as the “ bobble-head doll syndrome” has been described in suprasellar arachnoid cyst. The nodding or bobbing consists of irregular involuntary head motions in the anteroposterior direction occurring two to three times per second.The motion is reminiscent of that seen in dolls with a weighted head resting on a coiled spring; hence the name of this syndrome. Some degree of mental retardation is associated with this syndrome.

Treatment of suprasellar sella turcica arachnoid cysts are ;endoscopic ventriculostomy with concomitant fenestration of lamina terminalis, subfrontal cyst excision with communication to the basal cisterns, and transcallosal or transventricular cyst excision with concomitant cystoperitoneal shunting.

Treatment of intrasellar sella turcica arachnoid cysts is trans-sphenoidal approach with packing of sella with fat or fascia or muscle tissue.

Arachnoid cysts in Interhemispheric Fissure

Two types of arachnoid cysts occur near the midline in the supratentorial space.

1.       Interhemisheric cysts with associated partial or complete corpus callosal agenesis.It straddles the falx and extends equally on either side, compressing the medial surface of both hemispheres. A coronal MRI shows a “ bat-wing” appearance of the lateral horns and dorsal displacement of the third ventricle.

2.       Parasagittal cysts are usually not associated with agenesis of the corpus callosum. The cyst is strictly unilateral and is sharply limited by falx in the midline, thus it tends to be wedge shaped. There is a marked bulging of the frontal and parietal bones in the parasagittal area. The superior sagittal sinus and falx cerebri are considerably off the midline.

Cerebral convexity arachnoid cyst

In infants, it may present with progressive asymmetrical enlargement of head. MRI findings may mimic subdural hygroma, but without an enhancing membrane

In adults, the lesion may present with seizures, headache , papilloedemaand progressive contralateral hemiparesis.  Skull films  may show erosion of the inner table of the skull. CT scan shows biconvex or semicircular area of lucency over the convexity without an enhancing membrane. Surgical therapy consists of excision of the outer membrane of the cyst.

Quadrigeminal cistern arachnoid cysts

These cysts behave like pineal masses and present with hydrocephalus and Parinaud’s syndrome. Therapy consists of excision of the cyst wallthrough an occipital transtenorial approach, with or without insertion of cystoperitoneal shunt.  

Cerebellopontne angle arachnoid cysts

Clinical presentation of arachnoid cyst in CP angle may mimic that of an acoustic neuroma.

Posterior fossa arachnoid cysts

Posterior fossa arachnoid cysts may present in the midline near the fourth ventricle or the cistrna magna, or paramedian area opposite the cerebellar hemisphere. X-ray skull may show a focal expansion of the occipital bone. Diffrential diagnosis of midline posterior fossa arachnoid cyst include mega cistern magna, Dandy-Walker malformation, epidermoid cyst, cystic glioma and hemangioblastoma.

Clival region arachnoid cysts

The clival region is uncommon site for intracranial arachnoid cyst. Although termed clival , the cyst may extend into the interpeduncular cistern or the cerebellopontine angle. The cyst displaces the midbrain and pons dorsally along with basilar artery.The cranial nerves are stretched , elongated , and draped around the cyst.

Other rare locations of arachnoid cysts are  intraventricular, diploic space, etc.

                                         Diagrammatic representation of 3 types of Sylvian fissure arachnoid cyts

Diagrammatic representation of probable mechanism of formation of ependymal cyst 

Two types of interhemisheric arachnoid cysts

   

Ependymal cysts

Ependymal cysts may mimic arachnoid cyst clinically and on imaging studies. They occur much less frequently than arachnoid cysts. They occur in central white matter of the frontal and temoporopatrietal lobes, causing progressive neurological deficits, seizures and features of raised intracranial pressure. The protein content of the cyst fluid is generally greater than that of the CSF; on MRI the cyst will typically appear isointense or slightly hyperintense to CSF on proton density images. The wall is lined by columnar or cuboidal cells with or without cilia. Blepharoplasts may or may not be identifiable , These cysts never communicate with the ventricular system. They are believed to arise by the sequestration of a small segment of the primitive ependymal lining into either the cortical mantle or the perimedullary mesh . treatment consists of drainage of the cyst and excision of its wall.

Sources

Neurosurgery, second edition, volume III Editors: Robert H.Wilkins and Setti S.Rengachary, McGraw –Hill, Chapter 374; Intracranial arachnoid and ependymal cysts by Setti S. Rengachary and Jerome D.Kennedy, pages 3709-3728

Wikipedia

Handbook of neurosurgery , Mark S Greenberg, 7^th edition, Thieme