Morphologic and radiologic anatomy of the occipital bone.

Several diseases may cause craniovertebral instability warranting occiput-cervical fusion. As occipital screw and rod constructs are becoming more popular, requiring that screws be placed either medially or laterally in the occipital bone, the need for clearer anatomical and computed tomography (CT)-confirmed data regarding the relative thickness of the occiput in its various localities has become more critical. In 18 cadaveric specimens, the occipital bone was divided into 35 measurable segments. Transversely, the occipital bone was divided into five lines starting at the level of the inion; horizontal lines then proceeded inferiorly in 1-cm segments, 1, 2, 3, and 4 cm below the level of inion. In a comparable fashion, the occipital bone was divided vertically, starting at the midline, and proceeding laterally also in 1-, 2-, and 3-cm segments. Anatomical measurements of thickness were directly performed using a Vernier caliper. Results were directly correlated with axial CT measurements of bony thickness. Anatomical and CT measurements closely correlated within the same specimen, but there was significant interspecimen variability. The marked differences in the occipital bone anatomy noted between specimens indicates that patients undergoing occipital screw placement for cranial-cervical instability would benefit from preoperative occipital CT evaluations.     

Sudden unconsciousness during a lesser occipital nerve block in a patient with the occipital bone defect.

Occipital nerve block is usually considered to be a very simple and safe regional anaesthetic technique. We describe a case of sudden unconsciousness during a lesser occipital nerve block in a patient with an occipital bone defect. A 63-year-old man complained of headache, which was localized to the right occipital region. A right lesser occipital nerve block with a local anaesthetic was performed for treatment. During the lesser occipital nerve block, the patient suddenly became disturbed and lost consciousness. Two hours after the incident, the patient was fully awake without neurological sequelae. He had previously undergone a microvascular decompression for right trigeminal neuralgia. The patient had a bone defect following craniotomy. We believed that the loss of consciousness during lesser nerve block may be due to a subarachnoid injection. Occipital nerve block is relatively contraindicated in the presence of a bone defect.     

Aneurysmal bone cysts of the occipital bone

Two cases of aneurysmal bone cysts are reported. Each patient presented with a palpable mass in the occipital region and signs of compression of structures in the posterior fossa. One of the cases is unique, in that the aneurysmal bone cyst was associated with an epidural hematoma in the posterior fossa. The pertinent literature is reviewed.     

Elevation of the petrous bone caused by hyperplasia of the occipital bone presenting as hemifacial spasm: diagnostic values of magnetic resonance imaging and three-dimensional computed tomographic images in a bone anomaly

A case of elevation of the petrous bone due to hyperplasia of the occipital bone presenting as hemifacial spasm is reported. A 44-year-old man sought treatment for twitching of the buccal muscles on the right side that progressed rapidly in severity within 2 weeks of the onset. The anatomical details of the petrous and occipital bones were delineated clearly by computed tomographic scans of a bone window level. Details of the brain stem were shown by magnetic resonance images. The bone anomaly was displayed more realistically by three-dimensional computed tomographic reconstructions. The faithful representation of structures with these radiological studies should be mandatory, to prepare the surgical planning of such a complicated bone anomaly.     

Anatomical analysis of the occipital bone in patients with basilar invagination: a computed tomography-based study

BACKGROUND CONTEXTThe occipital bone is often involved in the surgical treatment of basilar invagination (BI). However, the anatomy of the occipital bone associated with BI patients has yet to be investigated.PURPOSETo present a morphological map of the occipital bone in BI patients and help guide screw placement for occipitocervical fusion.Study DesignA retrospective case-control study.METHODSRadiological measurements of the occipital bone were performed on computed tomography images based on a matrix of 99 points centered around the external occipital protuberance (EOP) in a cohort of 50 BI patients and 50 cases with no head and cervical disease. The comparison between the BI group and the control group was assessed using Student t analysis and p<.05 was considered statistically significant.RESULTSAll thicknesses measured from points of the matrix in the BI group were thinner than those in the control group (p<.05). The maximum thicknesses in both groups were located at the center of the EOP, which were 15.11±2.84 mm in the BI group and 17.56±3.03 mm in the control group, respectively. Additionally, thickness decreased with the distance away from the center of EOP.CONCLUSIONSThe occipital bone in BI patients is thinner than that in the general population. A limited safe zone in BI patients is available for surgeons to place screws, which may need to be fully evaluated before operation.     

Intradiploic epidermoid cyst of the occipital bone

BACKGROUND: A rare case of intradiploic epidermoid cyst of the occipital bone is described and recent literature, which emphasizes the radiological evaluation and surgical treatment of this lesion is reviewed. CASE DESCRIPTION: A 56-year-old female patient complained of headache and occasional episodes of vertigo for one year. Computed tomographic scan and magnetic resonance imaging were performed. The patient underwent occipital right craniotomy followed by total removal of the cyst and its capsule. RESULT: The postoperative course was uneventful and the patient was discharged 4 days later. CONCLUSION: A review of the literature shows that intradiploic epidermoid cyst of the occipital bone is rare. Correct radiological assessment and complete excision of this lesion and its capsule provides complete recovery.     

A case of giant osteoma in the occipital bone

A 51-year-old female patient, admitted with a chief complaint of dizziness, had bulging of the occipital area, which had started insidiously. On admission, a bony hard swelling with a smooth surface was noted in the left occipital region, extending over the midline of the skull. Plain X ray films revealed a uniform shadow of an osteoid mass inside the occipital bone. A tomogram indicated that the mass originated in the diplo? or outer table of the skull, although there was no evidence of destruction of the inner table. CT scan revealed mixed density mass with high density of bone and an irregularly shaped low density area. In the T1-weighted images of MRI, the entire mass showed a low intensity, while in the T2-weighted image the mass showed 3 areas with different intensities. Bone scintigraphy was performed with 99mTc-MDP and revealed an image of accumulation in the mass. Carotid and vertebral angiograms were negative for evidence of feeding arteries to the mass, for tumor stain, and for occlusion of either sigmoid sinus or transverse sinus. The mass was diagnosed as a giant osteoma, and was totally removed. The excised tumor measured 10 x 9 x 5 cm, and inspection at operation revealed it to be composed of a fragile osteoid portion and a comparatively soft connective tissue portion. The histological diagnosis of the mass was that it was a spongy osteoma including a comparatively large amount of connective tissue. The postoperative recovery of the patient was satisfactory and her dizziness disappeared.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ossifying fibroma of the occipital bone.

A rare ossifying fibroma in the occipital bone is described, and the available literature reviewed. The rapid growth seen in this case was remarkable and led us to believe this was a malignant osteogenic tumor. Full knowledge and the correct diagnosis of ossifying fibroma should have prevented an unnecessarily extensive operation for this benign lesion.     

Malignant fibrous histiocytoma of the occipital bone with intracranial extension--case report.

The authors present a rare case of malignant fibrous histiocytoma originating in the cranial bone. A 72-year-old male was admitted with a diffuse painless swelling in the left occipital region but no neurological abnormality. Plain skull x-ray films and computed tomographic scans showed a large tumor in the left temporo-occipital bone. The tumor invading subcutaneous tissue was totally excised and histologically diagnosed as malignant fibrous histiocytoma. Postoperatively, 40-Gy irradiation was given to the left temporo-occipital region. Several months later, however, the tumor recurred in the posterior fossa. Neuroradiological examination showed tumor extension into the occipital bone and muscle and the subdural space of the posterior fossa. A second operation extirpated all tumors except in the cerebellum. He died of pneumonia on the 14th postoperative day. Autopsy revealed malignant fibrous histiocytoma invading into the bilateral cerebellar hemispheres. Radiation and chemotherapy should be given as soon as possible following extensive surgery for malignant fibrous histiocytoma of the cranial bone.     

Massive plexiform neurofibroma with associated meningo-encephalocoele and occipital bone defect presenting as a cervical mass.

The commonest skull manifestations in neurofibromatosis involve the orbit, with very few reports about occipital defects. We report a rare case of a 54-year-old lady with a massive plexiform neurofibroma extending from the auricular region down her left neck and into her shoulder, with an associated large left occipital and left petrous bone defect and extensive cerebellar meningo-encephalocoele, which presented with a relatively asymptomatic cervical mass and was treated with resection of the neurofibroma and advancement and rotational skin flaps.     

Rotational vertebral artery occlusion from occipital bone anomaly: a rare cause of embolic stroke. Case report

Vertebral artery (VA) occlusion by rotation of the head is uncommon, but can result from mechanical compression of the artery, trauma, or atlantoaxial instability. Occipital bone anomalies rarely cause rotational VA occlusion, and patients with nontraumatic intermittent occlusion of the VA usually present with compromised vertebrobasilar flow. A 34-year-old man suffered three embolic strokes in the vertebrobasilar system within 2 months. Magnetic resonance imaging demonstrated multiple infarcts in the vertebrobasilar territory. Angiography performed immediately after the third attack displayed an embolus in the right posterior cerebral artery. Radiographic and three-dimensional computerized tomography bone images exhibited an anomalous osseous process of the occipital bone projecting to the posterior arch of the atlas. Dynamic angiography indicated complete occlusion of the left VA between the osseous process and the posterior arch while the patient's head was turned to the right. Surgical decompression of the VA resulted in complete resolution of rotational occlusion of the artery. An occipital bone anomaly can cause rotational VA occlusion at the craniovertebral junction in patients who present with repeated embolic strokes resulting from injury to the arterial wall.     

Epidermoid tumor of the occipital bone

Intradiploic epidermoid-tumor of the occipital bone was presented. There were neither intracranial extensions nor neurologic deficits. The lesion started as a painless mass under the scalp.The total removal of the tumor was associated with a good prognosis.     

Screw fixation via diploic bone paralleling to occiput table: anatomical analysis of a new technique and report of 11 cases

Several types of posterior approaches have been adopted for occipitocervical fusion. Prior to this study, Foerater et al. in 1927 used a fibular strut graft in the site between the occiput and the lower cervical spine to achieve fusion. Since then, various techniques including wrings, Hartshill loop, AO reconstructive plate, and AXIS occipital plate were described and used widely. As far as we know, all these techniques involve the screw placement vertical to the diploic bone; however none has ever addressed the feasibility of screw placement in occiput parallelling to the diploic bone. In our study, 30 dry specimens of human occiputs were measured manually using vernier calipers and protractors. The intradiploic screw was first supposed to be inserted inferiorly to the superior nuchal line (SNL) prominence. The entry point located at the superior edge of the SNL prominence. Afterward, the measurements of extracranial occiput in SNL area on midline and bilateral 15 mm to the midline saggital-cutting planes of the occiput were conducted. The thickness of the occipital bone at the location of SNL prominence, the entry point, the exit point and the screw orientation were measured, respectively. Afterward, 11 patients with craniocervical malformation were treated surgically using this alternative and their X-ray radiographs and CT scans were evaluated postoperatively. The data showed that the occipital at the site of SNL prominence was the thickest. The thickest point was external occipital protuberance (EOP), which was up to 14 mm. The thickness decreased gradually from the site of SNL to the superior border of surgical decompressed area. The actual length of screw channel was about 26 mm. The mean thickness for safe screw insertion ranged from 5.73 to 14.14 mm. A total of 22 intraocciput screws parallel to diploic bone were placed precisely, without injury to the cerebral and inner occipital venous sinus. The results confirm that occiput is available for holding intraocciput screw paralleling to diploic bone.     

Benign chondroblastoma of the occipital bone

We report the case of a 14-year-old boy with benign chondroblastoma in the occipital bone associated with a cerebellar hemorrhage. The clinical features, radiologic and histologic appearances, and histogenesis in this case are described. Other reports of benign chondroblastomas of the cranial bones are also discussed.     

Hyperostotic paraganglioma of occipitotemporal bone

A 25-year-old male presented with off-and-on vertigo of 10-year duration. He had left-sided cerebellar signs, left vocal cord paresis, and minimal left-sided hearing impairment. Computed tomography of the head revealed significant hyperostosis of squamous occipital, mastoid, and petrous temporal bone with no adjacent soft tissue mass. On excision, it turned out to be paraganglioma. Paraganglioma as a pure bony mass is not reported in the literature. The site of origin of such a tumor could not be ascertained, even on generous screening. The tumor remained nonsecretory on clinical and biochemical investigations.     

A case of malignant lymphoma in the skull after head injury associated with multiple bone tumors

A case of malignant lymphoma in the skull after head injury associated with whole bone metastasis is reported. The patient was a 66-year-old man who was admitted to Almeida Memorial Hospital because of headache and general fatigue 2 months after head injury. After admission tumors appear in the frontal and occipital region and grew rapidly. Plain craniogram revealed large map-like bone destructions and multiple punched out lesions. Bone scintigram with 99mTc-MDP revealed multiple accumulations of RI in the skull, vertebrae, ribs and pelvis. CT scan revealed destructive, markedly enhancing bone tumor which was compressing the brain as an extradural mass in the left frontal and occipital regions. Pathological examination of the tumor revealed malignant lymphoma of non-Hodgkin type and diffuse pleomorphic type. Though combination chemotherapy with ACNU, FT 207, PSK, CHOP (Cyclophosphamide, Adriamycin, Vincristine and Predonisone) and Acracinomycin A was performed after operation, and brought forth regression of tumor size and improvement of clinical symptoms transiently, he died 6 months after the onset because of recurrence in many bones with pathological fracture and complications such as pneumonia, DIC and acute renal failure. At autopsy the tumors were found to be localized only in the bones, but in none of lymphnode or visceral organs. Malignant lymphoma appearing initially as a skull tumor is rare, and its diagnosis and treatment were discussed.     

Plasma cell tumor of the parieto-occipital bone; a case report]

Plasmacytoma originating in the cranial bone is a rare disease. A report is presented of a case of plasmacytoma originating in the parieto-occipital region. The patient was a 62-year-old male with palpation of a parieto-occipital mass as chief complaint. He showed no neurological deficit. Ig-G in the serum was 2240 mg/dl, and M-protein (n-type) was demonstrated in the serum. Bence-Jones protein was negative and bone marrow was normal. Skull X-ray showed osteolytic change in the parieto-occipital region. CT scan and MRI demonstrated a markedly enhanced mass extending from the epidural to the subcutaneous space at the parieto-occipital region. Common carotid angiography showed remarkable tumor stain flowing from the occipital artery, the superficial temporal artery, and the middle meningeal artery. Following embolization of the bilateral occipital artery, parieto-occipital horse shoe scalp incision was done. The tumor was elastic soft and bled easily around the margin of destroyed bone. Subtotal removal of the tumor was accomplished. The removed surgical specimen of the tumor was found to be plasmacytoma. The patient's postoperative course was favorable and no neurological deficit was found. Laboratory studies revealed a remarkable reduction of Ig-G in the serum to 1170 mg/dl. Six months after the operation, no signs of recurrence were seen on CT scan. Plasmacytoma originating in the cranial bone is so rare that only 18 cases have been reported to date. In these cases, laboratory studies have shown no evidence of anemia, Bence-Jones protein in urine, and abnormality of the bone marrow which are characteristic of multiple myeloma.(ABSTRACT TRUNCATED AT 250 WORDS)     

Giant intradiploic epidermoid tumor of the occipital bone: case report

The authors describe a case of a giant intradiploic epidermoid cyst of the occipital bone with an intracranial extension in the posterior fossa and no signs of neurological involvement. The lesion started as a painless lump under the scalp. Roentgenographic and computed tomographic findings led to a correct diagnosis, and the complete removal of the cyst was accomplished, despite its large size. The total removal of these cysts is associated with a good prognosis.     

Traumatic occipital condyle fracture, multiple cranial nerve palsies, and torticollis: a case report and review of the literature.

A 32-year-old man sustained a unique combination of injuries: an occipital condyle fracture, left tenth to twelfth cranial nerve palsies, and chronic torticollis secondary to atlantoaxial rotatory fixation. Computed tomography (CT) demonstrated a triangular fragment of bone in the posterior fossa, and three-dimensional CT-reconstructed images confirmed the bone fragment to be from the occipital condyle. The patient made a good recovery with conservative management. Few occipital condyle fractures have been reported, and they should be suspected in patients who sustain painful neck and lower cranial nerve palsy following trauma. CT and plain films are complementary in confirming the diagnosis.     

Primary hemangioma of the occipital bone in the region of the torcula--two case reports

Two rare cases of subtorcular occipital bone hemangioma occurred in 26-year-old and 30-year-old female patients. Partial resection was performed in both cases because of the proximity to the torcula. No recurrence was seen at follow-up examination at 9 and 12 months.