General
- Parasag meningiomas have higher incidence of G2/G3 meningiomas when compared with meningiomas in other locations.
Grade 1 | 79.6% |
Grade 2 | 14.8% |
Grade 3 | 3.7% |
Numbers
- Represent 21 to 31% of intracranial meningiomas.
- Most prevalent location of meningiomas
- Due to high density of arachnoid cap cells
- Incidence according to Cushing and Eisenhardt classification
- Rt (59%) > Lt side (33.3%)
- Bilateral tumours 7.7%
Location | Definition | Frequency (%) |
Anterior 1/3 | Between the crista galli and the coronal suture | 14.8 to 33.9 |
middle 1/3 | From the coronal to the lambdoid suture | 44.8 to 70.4 |
posterior 1/3 | From the lambdoid suture to the torcula | 9.2 to 29.6 |
Origin
- Arises from dura of the SSS
- ~15% of tumours presenting with invasion of the SSS.
Histopathological
Histological type | No. of cases |
Transitional (mixed) | 87 |
Fibrous (fibroblastic) | 28 |
Atypical | 26 |
Meningothelial | 21 |
Psammomatous | 6 |
Malignant | 5 |
Secretory | 4 |
Microcystic | 2 |
Hemangiopericytoma | 2 |
Angioblastic | 2 |
Chordoid | 1 |
Total | 184 |
Natural history
- Infiltration of the SSS as a major factor related to recurrence of parasagittal meningiomas.
- Since then it is known that the extent of surgical resection and pathological grade correlates with the rates of recurrence
- Low risk of recurrence
- WHO grade I
- Psammomatous tumours with a high density of calcification
- High risk
- Angioblastic meningiomas
Classifications
- Brotchi classification
- Type I: Tumor is attached to the outer surface of the sinus
- Type II: Tumor enters the lateral recess of the SSS
- Type III: Tumor invades one wall of the SSS
- Type IV: Tumor invades two walls of a still patent sinus
- Type V: Tumor spreads over the midline, invades the three walls, and occludes the SSS
- Sindou and Alvernia Classification
- Type I: Tumor attaches to the outer surface of the sinus wall
- Type II: Tumor fragment inside the lateral recess
- Type III: Tumor invades the ipsilateral wall
- Type IV: Tumor invades the lateral wall and roof
- Type V: Complete sinus occlusion with one free wall
- Type VI: Complete sinus occlusion without any free walls
Clinical features
- Presenting symptomatology is largely related to the proximity of the lesion to the Rolandic fissure
- Middle 1/3 present earlier
- Typically present with sensory or motor seizures involving the contralateral lower extremity.
- After seizures, contralateral hemiparesis constitutes the second most common presenting symptom, followed by paresthesias, papilledema, and dementia
- Posterior 1/3 present later
- Homonymous hemianopsia
- Anterior 1/3 present later
- Frontal lobe symptoms
- Headache
- Common symptoms in location along the superior sagittal sinus
- Adapted from Gauthier-Smith.¹⁵
ㅤ | Anterior third (50 cases) | Middle third (89 cases) | Posterior third (14 cases) | Total (153 cases) |
Focal seizures | 1 (2%) | 29 (33%) | 3 (21%) | 33 (22%) |
Generalized seizures | 13 (26%) | 10 (11%) | - | 23 (15%) |
Headache | 18 (36%) | 9 (10%) | 5 (36%) | 32 (21%) |
Confusion/cognitive decline | 18 (36%) | 6 (7%) | 3 (21%) | 27 (18%) |
Monoparesis (leg) | 2 (4%) | 23 (26%) | - | 25 (16%) |
Hemiparesis | - | 6 (7%) | 2 (14%) | 8 (5%) |
Monoparesis (arm) | 1 (2%) | 1 (1%) | - | 2 (1%) |
Visual symptoms | 1 (2%) | 4 (5%) | 3 (21%) | 8 (5%) |
Calvarial deformity | 6 (12%) | 2 (2%) | - | 8 (5%) |
Dysphasia | - | 4 (4%) | - | 4 (3%) |
Stroke | - | 2 (2%) | - | 2 (1%) |
Vertigo | - | 1 (1%) | - | 1 (1%) |
Other symptoms | 7 (14%) | 11 (12%) | 3 (21%) | 21 (14%) |
Anatomical consideration
- Cross-sectional analysis of the SSS reveals a basic triangular shape that gradually increases in size as it extends distally toward the posterior third.
- Anterior half of the SSS: (vs the posterior half)
- Narrower
- Fewer associated venous lacunae
- Fewer pacchionian bodies (Arachnoid granulation)
- Smaller numbers of adjoining cortical veins entering the sinus
- This facilitates surgical exploration.
- Irregular interdural venous lacunae
- Communicates with the SSS laterally
- Lie on either side of the dura mater
- Occasionally accompanied by arachnoid granulations.
- Appear as a filling defect or an intrasinusal mass on MRI.
- 8 to 12 external medial cortical veins and a similar number of internal cortical veins carry out most cortical venous drainage on each hemisphere.
- Parasagittal veins
- 70% parasagittal veins join the SSS in a segment of the sinus located between the coronal suture and 2 cm behind it.
- 53% venous tributaries entered SSS within 2 cm of the coronal suture,
- 76% venous tributaries entered SSS within 2 cm behind the coronal suture.
- Venous collateral anatomy
- Anterior 1/3 tumours
- Collateral drainage occurred through cortical veins in 52.1% of cases.
- Middle or posterior 1/3 tumors
- Collateral drainage occurred through cortical veins in 67% of cases.
- Collateral blood flow through the extracerebral veins
- Through meningeal veins and end-to-end anastomoses of superficial cerebral veins
- Occurred in 56% of patients regardless of the location along the sinus
- Superficial cerebral veins are classified into four groups depending on the cortical area drained by them:
- Superior sagittal group that drains the superior part of the medial and lateral surfaces of the frontal, parietal, and occipital lobes and the anterior part of the basal surface of the frontal lobe and empties into the SSS;
- Sphenoidal group that drains into the sphenoparietal and cavernous sinuses;
- A tentorial group that converges on the tentorial sinuses;
- A falcine group that empties into the inferior sagittal or straight sinus.
- Resection of the anterior third of the sinus has limited impact on the overall hemispheric venous drainage in most cases, and that sacrifice of the middle third of the SSS significantly affects venous return.
- Parasagittal veins divided into
- Anterior frontal
- Had an average of 6.5 veins on each hemisphere
- Posterior frontal
- Had three veins
- Parietal
- Had four veins
- Occipital
- Had one vein.
- Disruption of venous structures in the posterior third results in less restrictive venous drainage than sacrifice of middle third structures, but the true effect of these changes is directly related to the caliber of the sacrificed vessel and the cortical region draining through it.
Assessment
Radiological
CT
- Aid in planning of the craniotomy flap
- CT data can be used to fashion precise prosthetic implants for cranioplasty
MRI
- Functional MRI and fiber tractography has been reported and could be beneficial in patients with parasagittal tumors that invade beyond the pial surface
Venography
- CTV/MRV
- Can provide preoperative insight on venous infiltration and visualize collateral venous anastomoses
Angiography
- MRA
- Accurate, noninvasive visualization of the arterial and venous anatomy,
- Facilitates
- Analysis of sinus patency and invasion,
- Visualization of collateral venous drainage patterns that develop following sinus occlusion.
- DSA
- Indication
- MRA data is not enough
- Need for embolization
- Venous
- To investigate
- Patency of the sinus
- Arterial tributaries to the tumor and its relationship with cortical structures,
- Location of cortical draining veins and their point and angle of entry into the SSS are carefully considered
- Findings related to venous flow rerouting secondary to partial or complete SSS occlusion,
- Nonvisualization of the occluded segment
- Failure of cortical veins to reach the SSS
- Delayed emptying of veins at the site of obstruction
- Reversal of normal venous flow with collateral venous channels connecting the SSS with other venous structures
- Such as the lateral sinus and the middle cerebral vein
- Thalamostriate vein can also be depressed in the more anteriorly located lesions; this finding was often referred to as “closing of the venous angle
- Arterial
- For large meningiomas (> 5 cm)
- Determination of arterial feeding branches to the tumor, which may arise from the anterior or middle cerebral arteries, can facilitate preemptive intraoperative devascularization by selective embolization
Management
Observation
- Serial MRI/MRA imaging
- Yearly MRI follow-up for patients older than age 65 who are asymptomatic or have tumours less than 3 cm in diameter.
Surgery
- Decision based on
- Patient (e.g. social functions, occupation, hobbies, age),
- Tumour (e.g. anatomical location, size, speed of growth, presence of calcifications)
- Tumour effect on the surrounding tissues (e.g. brain oedema, SSS narrowing/ occlusion, presence of venous collaterals),
- Other available treatment options (surgery, fractionated radiotherapy, SRS, and venous stenting).
- Most commonly Simpson grade 2 is achieved
- Some cases residual tumour invading the wall or lumen of the SSS may have to be left behind.
- For these, adjuvant radiation treatment either at the outset or after progression on radiological surveillance should be considered on an individual basis.
- Pre op
- Endovascular
- Aim
- To reduce intraoperative blood loss and decrease surgical time in meningioma surgery
- Material
- Polyvinyl alcohol (PVA)
- Onyx
- Safer and newer
- Cons
- Tumour oedema or haemorrhage after embolization of meningiomas with polyvinyl alcohol (PVA) particles
- Technique
- Superselective angiography is performed through the microcatheter to verify the location and identify any normal branches, which would preclude safe embolization.
- The embolic material is injected under continuous realtime digital-subtraction fluoroscopy to allow penetration into the tumor bed, which will result in devascularization and subsequent necrosis.
- A palliative technique
- Aim
- Intracranial hypertension presents
- Despite surgical decompression
- Patient too comorbid to have surgery
- Despite VPS placement
- Cons
- Risk of poststenting thrombosis
- Need for anticoagulation followed by antiplatelet therapy
Embolization
Stenting
- Operative Approach
- Anterior 1/3 tumour
- Positioned supine with the head slightly flexed
- Middle 1/3
- Positioned supine or lateral with the area overlying the tumor positioned as the highest point in the vertical plane.
- Posterior 1/3
- Semisitting,
- This position maintains the midline in a vertical plane and facilitates anatomical orientation.
- Lateral,
- Three-quarter prone,
- Prone position with the tumor below the horizontal plane.
- This takes advantage of gravity-mediated retraction of the ipsilateral cerebral hemisphere, which facilitates dissection, particularly in lesions with significant falcine attachments.
- Allows for
- Smaller incisions, tailored craniotomies,
- Anatomical localization of eloquent cortex, which translates into decreased morbidity, faster healing times, and improved cosmesis.
- This technology is particularly useful in tumors that violate the pial surface and complements preoperative planning studies.
- 3 pins
- Two types
- A modified bicoronal skin incision is made for tumors in the anterior third of the SSS.
- A trapdoor or horseshoeshaped incision is made for tumors on the middle or posterior third of the SSS
- The incision extends at least 2 cm across the midline
- Careful dissection of the subjacent pericranium, which can later be used for dural reconstruction.
- When planning the incision and scalp flap elevation, the location of prominent scalp and diploic veins formed through collateralization must be observed because brisk bleeding can be encountered, and early obliteration of this collateral flow can result in significant cerebral edema.
- Most authors recommend multiple burr holes,
- Place burr holes right over the SSS by using controlled drilling with small drill bits and conduct the dural release from the inner table in a medial to lateral direction.
- Burr holes on both sides of the sinus and perform the dural dissection and the release of the sinus wall from lateral to medial until both parasagittal burr holes are communicated epidurally.
- Using an oscillating saw, without burr hole placement.
- The oscillating saw can be particularly useful when extending the craniotomy across the venous sinuses (Fig. 16.5) because dissection of the sinus wall from the inner table can be performed under direct visualization.
- Use of the Control Depth Attachment (CDA) available for the Anspach drill has further refined this technique.
- The length of this attachment can vary from 1 to 5 mm, and it allows the surgeon to cut through the outer table and the cancellous bone while sparing the inner table.
- The inner table is then fractured with an osteotome, which is used along the perimeter of the craniotomy.
- Great care is taken when the osteotome is used over the sinus (this segment can be avoided by continuing the osteotomy to the opposite side).
- 2 techniques
- Two stages
- First flap located on the side of the tumor ~1 cm lateral to the SSS. Following dissection of the dura overlying the sinus from the bone,
- Second flap is elevated crossing the midline to the contralateral hemisphere.
- One stage
- The parasagittal bone flap must be centered over the tumor utilizing frameless stereotactic guidance and surface landmarks.
- Bone flap should expose an area 2 to 3 cm anterior and 2 to 3 cm posterior to the tumor margins.
- Must cross the midline and should expose the contralateral hemisphere at least 2 cm beyond the edge of the sinus or the lateral extent of the tumor, whichever is more lateral. Direct visualization of the sinus wall during dissection remains as the primary principle of the craniotomy.
- Special attention is given to the contralateral dura and adjacent veins, and osteotomies over the SSS are performed last.
- Elevation of the bone flap can be complicated by
- Engorged diploic anastomosis
- Frequently encountered invasion of the dura and bone by the tumor.
- In cases of severe tumor-induced hyperostosis, the craniotomy flap can be planned around the tumor, and a central portion of bone can be left attached to the tumor until better SSS control can be obtained later in the dissection.
- Following elevation of the bone flap, hemostatic agents such as Gelfoam (Pfizer, Inc., NY) and Surgicel (Ethicon, Inc., Somerville, NJ) can be applied over the sinus and stabilized with cotton strips and gentle pressure.
- Careful monitoring of the precordial Doppler, pCO2, oxygenation, and hemodynamic parameters is particularly needed at this point because most air emboli will present during or immediately after flap elevation.
- Placing tacking sutures along the edge of the craniotomy can control intraoperative and postoperative epidural bleeding. If precordial Doppler or pCO2 anomalies indicate air embolism, a Valsalva maneuver enacted by the anesthesiologist can reveal the site of air penetration.
- A semilunar dural flap based along the SSS is elevated under direct microscopic visualization of the pial surface to avoid injury to cortical draining veins.
- The contralateral dura is opened in the same fashion but only when the tumor significantly involves the contralateral hemisphere.
- Dissection is initiated by visualization and preservation of the tumor capsule on the lateral margins.
- If the lesion is extrapial
- A surgical plane can be obtained and the space between the pia and the capsule can be developed with cottonoid strips, which are placed circumferentially from the periphery to the midline and mobilized toward the deeper planes as dissection progresses
- If the tumor has violated the pial surface,
- Gentle dissection with selective bipolar coagulation is used to separate the capsule.
- Tenting sutures can be placed on the lateral edges of the dural flap.
- These sutures are tagged to either bulldog or Kocher clamps rotated medially toward the contralateral hemisphere.
- The weight of the clamps on the dural flap serves to distract the tumor, which is usually well anchored to the dura, from the surrounding parenchyma.
- This helps find a dissection plane between tumor and brain.
- Debulk for tumors greater than 3 cm in diameter with ultrasonic aspiration or monopolar cautery
- Following internal debulking, dissection can proceed in a circular fashion, alternating from the lateral margin up to the anterior or posterior pole and down to the opposite pole until the deep aspect of the lesion is reached.
- If the SSS is not involved, cutting the dura parallel to the SSS after all parasagittal veins have been released completes the resection.
- General
- Sinus Management and Conservative Resection
- High-resolution imaging and stereotactic radiosurgery have allowed for less aggressive management of the intrasinusal components of parasagittal meningiomas.
- For lesions invading the superior sagittal sinus (SSS) wall that do not compromise its patency, surgeons may resect only the extrasinusal portion and monitor the residual tumour with periodic MRI/MRA follow-up.
- If growth of the residual tumour is detected during follow-up, stereotactic radiosurgery may be recommended before considering a second surgical resection.
- In cases where the SSS is completely obliterated, collateral anastomotic networks typically develop over time and can prevent symptomatic venous hypertension.
- If uncertain
- Treat it as partially occluded
- Routine exploration of the sinus through a short incision is often recommended because there are frequently discrepancies between preoperative imaging and intraoperative findings regarding the extent of sinus invasion.
- Venous bleeding during these procedures can be controlled by inserting hemostatic material, such as Surgicel, into the SSS lumen and the ostia of adjoining veins.
- If SSS completely occluded
- Can resect SSS tumour
- Before resecting an obliterated sinus, surgeons must perform a detailed assessment to ensure that venous collaterals are identified and preserved.
- The encased portion of the sinus is ligated at both the proximal and distal ends with heavy silk sutures before the falx is cut along the edge of the tumour.
- If SSS partially occluded
- Do not resect SSS tumour
- Subtotal resection can be
- Follow up radiologically
- Adjuvant RT
- Explanation
- Although opening of the SSS to remove intraluminal meningioma extension followed by suturing or patching is possible, it is liable to failure with thrombosis and has serious consequences, particularly if attempted on the posterior third of the SSS.
- Regrowth or recurrence that results in gradual and eventually total occlusion of the SSS would be amenable to a more radical resection at the second surgery.
- A conservative approach to allow for proper collateral circulation to be established and for progressive sinus thrombosis to occur can significantly decrease morbidity
- Venous compromise caused by surgery
- Can lead to
- Temporary asymptomatic through symptomatic cerebral oedema
- Reversible neurological deficit caused by venous infarction,
- Haemorrhagic transformation of venous infarction
- Malignant brain swelling with the potential of severe permanent neurological deficit and mortality.
- In some cases, it may be appropriate to treat venous outflow obstruction by venous stenting
- If gross total resection is still pursued.
- Primary Repair and Grafting For lesions that invade only the lateral recess
- The lateral recess of the SSS: Are expansions known as lateral venous lacunae, which are irregular venous spaces in the dura mater flanking the sinus on either side.
- A “marginal resection” of the sinus is performed, which consists of resecting the corner of the lateral sinus invaded by the tumor.
- This is followed by placement of 3–0 Vicryl sutures at 5 mm intervals along the length of the sinus resection. The ends of these sutures are preserved; the tails are left long and tagged with bulldog or Kocher clamps. At the end of the operation these sutures are used to secure a dural graft to the sinus to complete the dural closure.
- Venous Reconstruction and Grafting Procedures
- Autologous vein grafts are typically harvested from the internal saphenous vein or the external jugular vein.
- It is critical to mark and maintain the original cephalocaudal orientation of a venous graft because internal valves determine the direction of blood flow.
- Reconstruction is performed using interrupted, loose circumferential sutures with nonabsorbable materials like 8-0 Prolene.
- Vascular clamps and aneurysm clips should be avoided because their crushing effect can injure the sinus walls and endothelium.
- Patches can be fashioned from pericranium, fascia lata, or fascia temporalis, with fascia temporalis considered a highly suitable material.
- While autologous materials like fascia or dura have shown high rates of angiographically confirmed patency, synthetic grafts like GoreTex have yielded poor results despite anticoagulation.
- Postoperative Management
- The clinical management of patients undergoing bypass procedures is complex and requires careful titration of blood pressure, volume status, and blood viscosity to prevent graft thrombosis.
- Anticoagulation therapy is mandatory for these patients, typically starting with heparin 24 hours after surgery for three weeks.
- Patients then transition to Coumadin for an additional three months until the sinus has achieved re-endothelisation.
- Flow restoration procedures are high-risk and require advanced preparation and training.
- All vascular structures must be identified and followed to determine their contribution to the tumor vasculature before coagulation because pericallosal and callosomarginal branches are frequently parasitized by these tumors and supply the inferomedial aspect of the lesions.
- Small lateral feeding branches are coagulated and divided.
- Meticulous preservation of all bridging veins is crucial;
- When a vein is invaded by tumor not easily removed with gentle dissection, most authors recommend leaving residual disease rather than sacrificing the vessel.
- This is particularly true at the anterior and posterior margins of the tumor (anterior and posterior pole), in which hypertrophic veins reaching the sinus are frequently encountered.
- Injury to critical venous structures (i.e., rolandic veins) can occur during dissection, and the surgeon must be prepared for a venous reconstruction to avoid a devastating venous hemorrhagic stroke in eloquent cortex.
- In cases that require SSS wall reconstruction, an end-to-end venous graft to the stump of the bridging vein can be performed.
- Can be performed with
- Pericranial graft harvested during the opening,
- Fascia temporalis if accessible through the opening incision
- Dural substitute such as
- Allogenic human skin (AlloDerm, LifeCell Corp., Palo Alto, CA),
- Bovine pericardium (Dura-Guard, Synovis, St. Paul, MN; Tutopatch, Tutogen Medical, Gainesville, FL),
- Bovine dermis (Durepair, Medtronic Sofamor Danek, Inc., Memphis, TN)
- Watertight closure is important, especially in patients with residual disease or higher-grade lesions in whom adjuvant radiosurgical therapy will be pursued.
- If tumor-induced hyperostosis is significant, the bone flap should be replaced by a cranioplasty, which can be performed with methylmethacrylate, titanium mesh, or other reconstructive materials
Patient Position
Intraoperative Neuronavigation
Surgical Incision
Craniotomy
With burrhole placement
Without burrhole placement (using an oscillating saw)
Elevation of the bone flap
Dural Opening
Tumor Resection
Dealing with intraluminal SSS meningioma (These may include venous channels in the falx and tentorium as well as emissary veins)
Dealing with vessels
Dural Closure
Bone replacement
Radiosurgery
- Indication
- Residual disease
- Should be given for all grade 3 meningiomas
- Grade 2 controversial
- Best to follow up with MRI first before deciding
- Recurrent disease
- First line of treatment in symptomatic patients with high preoperative risks (advanced age, multiple comorbidities, poor performance status).
- Technique
- Fractionated stereotactic radiation delivered by a linear accelerator (LINAC) without or with robotic assistance (Cyberknife)
- Intensity-modulated radiotherapy (IMRT)
- Tomotherapy
- Single-dose gamma therapy via gamma-knife radiosurgery.
- Tumor control rate
- SRS as first-line therapy: 93 ± 4%
- SRS as adjuvant therapy after surgery: 60 ± 10%
- Radiosurgery
- Effective treatment for tumors less than 3 cm in diameter.
- Risk of
- Higher incidence of symptomatic post-treatment peritumoral edema
- More prevalent with
- Larger tumors
- Higher prescription doses are given.
Chemotherapy and Other Adjuvant Treatments
- Treatment of recurrent or high-grade meningiomas remains a challenge.
- A specific study of chemotherapeutic agents for treatment of recurrent or high-grade parasagittal meningiomas has not been performed, but patients with parasagittal meningiomas have been moderately represented in previous trials of recurrent meningiomas gathering multiple locations.
Outcome
- Raza and Colleagues
- 110 patients with parasagittal meningiomas who underwent surgery at Johns Hopkins Hospital.
- GTR was pursued for all lesions invading the sinus, without flow restoration.
- Residual or recurrent lesions were observed and managed with radiosurgery if progression was detected.
- Patients with a minimum of 24 months of follow-up (n = 61) were further analyzed. Mean follow-up was 41 months.
- All patients underwent surgical resection, and those exhibiting residual/recurrent disease were treated with radiosurgery if indicated (19.6%).
- Pathological examination showed 80% grade I meningiomas, 13% grade II, and 7% grade III.
- Simpson grade I/II resections were achieved in 81% of the patients.
- Major complications consisted of venous thrombosis/infarction (7%), intraoperative air embolism (1.5%), and death (1.5%). The recurrence rate was 11%, and the rate of improvement on Karnofsky Performance Status (KPS) was 85%.
- Surgical series of Parasagittal Meningiomas (1955 to 2010)
Authors | Year | No. of cases | Recurrence rate (%) | Median follow-up (years) | Overall mortality (%) |
Hoessly and Olivecrona | 1955 | 196 | 6 | 5 | 12.3 |
Simpson | 1957 | 107 | 19 | 5 | – |
Logue | 1975 | 91 | 11 | – | 4.4 |
Bonnal and Brotchi | 1978 | 21 | 14 | – | 4.7 |
Kropp et al | 1978 | 96 | 16.6 | 7 | – |
Yamashita et al | 1980 | 80 | 14.6 | 5 | – |
Chan and Thompson | 1984 | 16 | 13 | – | – |
Giombini et al | 1984 | 243 | 17.7 | 5 | – |
Mirimanoff et al | 1985 | 38 | 24 | 10 | – |
Jääskeläinen et al | 1986 | 136 | 8 | – | – |
Philippon et al | 1986 | 153 | 14.4 | 10 | – |
Baird and Gallagher | 1989 | 46 | 23.9 | – | – |
DiMeco et al | 2004 | 108 | 13.9 | 13 | 2 |
Sindou and Alvernia | 2006 | 100 | 4 | 8 | 3 |
Colli et al | 2006 | 53 | 32.7 | 7.8 | 1.9 |
Raza et al | 2010 | 61 | 11 | 4.4 | 1.5 |
DiMeco et al | 2010 | 184 | 12.5 | – | 1 |
Differential diagnosis
- Hemangiopericytomas
- Lymphomas
- Metastatic disease
- Extramedullary haematopoiesis
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