Intraosseous lipoma of the sphenoid bone causing optic nerve compression: A case report

Abstract

BACKGROUND

Intraosseous lipomas are rare developmental anomalies that present with visual impairment. Due to their infrequency, they often pose diagnostic challenges, particularly in differentiating them from more common optic nerve pathologies. Magnetic resonance imaging (MRI) plays a crucial role in the early identification and management of these lesions.

CASE SUMMARY

We present the case of a 41-year-old male with a history of dyslipidemia who developed sudden onset headaches and decreased vision in his left eye. MRI revealed a T1-hyperintense fat-containing lesion within the left anterior clinoid process of the sphenoid bone at the optic canal, causing extrinsic compression of the left optic nerve, initially interpreted as a lipoma. Intraoperatively, the previously thought lipoma lesion was actually shown to be adipose tumor of the bone and pathological examination confirmed the diagnosis. The left optic nerve was successfully decompressed, and the patient’s vision improved significantly post-op. This case highlights that while MRI is essential in evaluating optic nerve compressive lesions, radiologic findings alone may be insufficient, and surgical and pathological correlation remains crucial for accurate diagnosis.

CONCLUSION

This case highlights the importance of considering intraosseous lipoma of the sphenoid bone as a rare cause of optic nerve compression and emphasizes the pivotal, but not definitive, role of MRI, which must be complemented by surgical and histopathological correlation to prevent irreversible visual loss.

Key Words: Intraosseous lipoma; Sphenoid bone; Optic nerve compression; Adipose tumor of bone; Reversible vision loss; Magnetic resonance imaging; Case report

Core Tip: This case report describes a rare intraosseous lipoma of the sphenoid bone causing compressive optic neuropathy and reversible vision loss in a middle-aged patient. Magnetic resonance imaging (MRI) suggested a lipomatous lesion, but definitive diagnosis required intraoperative findings and histopathological confirmation of an adipose tumor of bone. Successful optic nerve decompression led to significant visual recovery. This case underscores the need to consider intraosseous lipoma in the differential diagnosis of optic nerve compression and to correlate MRI with surgical and pathological findings.

INTRODUCTION

Intraosseous lipomas are rare benign tumors that arise within the medullary cavity of bone and are composed of mature adipocytes. They account for less than 0.1% of all primary bone tumors and are most frequently identified incidentally on imaging studies of the long bones, particularly the proximal femur, tibia, and calcaneus. When located in the skull base, intraosseous lipomas may remain asymptomatic or present with nonspecific symptoms. However, their proximity to critical neurovascular structures can lead to significant clinical manifestations. Compression of the optic nerve by such lesions is exceptionally uncommon, with only a few cases reported in the literature[1,2].

Compression of the optic nerve can result in significant visual morbidity and is typically associated with more common pathologies such as optic nerve gliomas, meningiomas, or inflammatory optic neuropathies[3]. Fat-containing lesions within the orbit or optic canal are uncommon and may lead to diagnostic uncertainty, particularly when their location within the bone obscures the typical characteristics seen in more superficial soft tissue lipomas. In this context, magnetic resonance imaging (MRI) plays a pivotal role. Its superior soft tissue contrast allows for the precise characterization of lesion content, extent, and its spatial relationship with critical structures, thereby guiding both diagnosis and surgical planning[4].

We present the case of a 41-year-old male with acute unilateral visual loss due to an intraosseous lipoma compressing the optic nerve at the optic canal. This case is notable for the rare location of the lipoma within the sphenoid bone, the diagnostic challenge it posed due to its imaging appearance, and the successful outcome following surgical decompression. The diagnosis was ultimately confirmed through histopathological evaluation, emphasizing the importance of correlating radiologic, intraoperative, and pathological findings when managing uncommon skull base lesions.

CASE PRESENTATION

Chief complaints

Acute unilateral visual loss in the left eye, associated with headache.

History of present illness

A 41-year-old male presented with a short history of progressive blurring of vision in his left eye. Over several days, he noticed difficulty with reading and with detecting objects in the left peripheral field, accompanied by intermittent headaches. He denied eye pain, diplopia, photopsia’s, or systemic constitutional symptoms such as fever or weight loss.

History of past illness

The patient had a history of dyslipidemia, controlled with medical therapy. He also had a remote history of significant ocular trauma to the right eye, resulting in traumatic optic neuropathy and no light perception vision in that eye. There was no history of diabetes mellitus, hypertension, malignancy, or prior intracranial surgery.

Personal and family history

He was a non-smoker and denied alcohol or illicit drug use. Family history was negative for hereditary optic neuropathies, intracranial tumors, or other significant neurologic or ophthalmologic disorders.

Physical examination

General and systemic physical examinations were unremarkable. Neurological examination showed no focal motor or sensory deficits. On ophthalmologic examination, best corrected visual acuity was no light perception in the right eye (Oculus Dexter) and 20/80 in the left eye (Oculus Sinister). The right pupil was non-reactive, consistent with longstanding traumatic optic neuropathy, while the left pupil was briskly reactive to light. Extraocular movements were full in both eyes.

Slit-lamp examination of the left eye revealed a quiet anterior segment without signs of inflammation. Funduscopic examination of the left eye showed marked optic disc swelling consistent with papilledema, whereas the right optic disc demonstrated chronic post-traumatic changes. Visual field testing of the left eye using octopus perimetry demonstrated a significant inferotemporal defect preoperatively, with substantial improvement after treatment, consistent with compressive optic neuropathy at the optic canal (Figure 1).

Figure 1 Visual field perimetry (octopus 101) demonstrating the preoperative and postoperative status. A: Left eye (Oculus Sinister) preoperatively, exhibiting significant visual field loss, particularly affecting the inferotemporal region; B: Left eye (Oculus Sinister) postoperatively, revealing marked improvement and substantial recovery of visual fields after surgical decompression.

Laboratory examinations

Routine laboratory investigations, including complete blood count, basic metabolic panel, and inflammatory markers, were within normal limits and did not suggest an infectious, inflammatory, or metabolic cause for the visual loss.

Imaging examinations

Urgent MRI of the brain and orbits with contrast revealed a T1-hyperintense, fat-containing lesion within the left anterior clinoid process of the sphenoid bone at the level of the optic canal, causing significant extrinsic compression of the left optic nerve (Figure 2). The lesion demonstrated signal characteristics compatible with adipose tissue on fat-sensitive sequences. No additional intracranial mass, acute ischemia, or hydrocephalus was identified.

Figure 2 T1-weighted magnetic resonance imaging scan showing a hyperintense fat-containing lesion within the left anterior clinoid process/sphenoid bone at the optic canal, causing extrinsic compression of the left optic nerve, consistent with an intraosseous lipoma.

These findings were most consistent with an intraosseous lipoma of the sphenoid/anterior clinoid process compressing the optic nerve, while acknowledging that other fat-containing lesions (e.g., dermoid cysts or lipomatous variants) can have overlapping imaging features.

MULTIDISCIPLINARY EXPERT CONSULTATION

The case was discussed at a multidisciplinary meeting involving neurosurgery, ophthalmology, and neuroradiology. Based on the acute unilateral visual decline, the presence of papilledema, visual field defect pattern, and MRI evidence of a fat-containing intraosseous lesion at the optic canal, the team concluded that the patient had a compressive optic neuropathy of the left eye secondary to an intraosseous lipoma of the sphenoid/anterior clinoid process.

Given the severity and rapid progression of visual loss, urgent surgical decompression via anterior clinoidectomy with unroofing of the optic canal was recommended to prevent irreversible optic nerve damage.

FINAL DIAGNOSIS

Intraosseous lipoma of the left sphenoid bone/anterior clinoid process causing compressive optic neuropathy of the left optic nerve with secondary papilledema.

TREATMENT

The patient underwent a left pterional craniotomy under general anesthesia. A combined extradural and intradural anterior clinoidectomy was performed with unroofing of the optic canal. The anterior clinoid process was carefully drilled and removed, exposing the optic canal, which was opened medially and posteriorly. Intraosseous fatty tissue consistent with lipoma was identified within the anterior clinoid/sphenoid bone and meticulously debulked, and the thickened, fatty dura overlying the optic nerve was opened to achieve full decompression.

The hybrid extra-/intradural technique allowed safe drilling of the anterior clinoid and complete decompression of the optic nerve while preserving adjacent neurovascular structures (Figure 3). Standard postoperative care was provided in the neurosurgical ward with close neuro-ophthalmologic monitoring.

Figure 3 Key surgical steps in extradural anterior clinoidectomy and optic nerve decompression. A: Extradural drilling of the anterior clinoid process using a diamond high-speed drill; B: Opening the optic canal with 1-mm Kerrison punch; C: Demonstration of extradural clinoidectomy and decompression of the optic canal; D: Opening the optic nerve dural sleeve; E: Use of a mini hook to verify complete optic nerve decompression intradural; F: Completely decompressed and free optic nerve, with adipose tissues (indicated by blue arrow) cleared away.

OUTCOME AND FOLLOW-UP

Postoperatively, the patient showed rapid visual improvement in the left eye. Best corrected visual acuity improved from 20/80 to 20/20 on follow-up. Papilledema resolved, and repeat Octopus perimetry demonstrated marked improvement and near-complete recovery of the inferotemporal field defect (Figure 1, postoperative field).

Follow-up axial T1-weighted MRI confirmed successful decompression of the left optic nerve with complete removal of the fat-containing lesion from the optic canal and no residual intraosseous lipoma (Figure 4). The patient remained neurologically stable and visually asymptomatic at subsequent outpatient visits, with no radiological evidence of recurrence during the follow-up period.

Figure 4 Postoperative axial T1-weighted magnetic resonance imaging demonstrating successful decompression of the left optic nerve canal and clearance of previously seen fat-containing lesion.

DISCUSSION

Intraosseous lipomas are rare benign tumors that arise within the medullary cavity of bone and are composed predominantly of mature adipose tissue. They represent approximately 0.1% of all primary bone tumors, with fewer than 300 cases documented in the literature. Involvement of the skull base with secondary optic nerve compression, as in our patient, is exceptionally rare. Although most frequently located in the metaphyseal regions of long bones such as the femur, tibia, and calcaneus, intraosseous lipomas have also been reported in the craniofacial skeleton, including the sphenoid and orbital bones. When situated in these less common sites, particularly near the optic nerve or other critical neurovascular structures, they may present with clinically significant symptoms including headache, visual disturbance, or cranial nerve deficits[5].

Histologically, intraosseous lipomas consist of mature fat cells and can exhibit a spectrum of degenerative changes such as fat necrosis, calcification, cystic transformation, and resorption of trabecular bone. These features have been classified by Milgram into three stages: Stage I lesions contain viable fat without necrosis, stage II lesions exhibit fat necrosis and focal calcification, and stage III lesions show extensive necrosis with cyst formation. This classification provides a framework for understanding the potential evolution and radiologic appearance of intraosseous lipomas[6,7].

MRI and computed tomography (CT) are essential tools for the diagnosis of intraosseous lipomas. On MRI, these lesions typically appear hyperintense on T1-weighted sequences due to their fat content and demonstrate signal loss on fat-suppressed images[8]. CT findings often reveal a well-defined lytic lesion with internal fat density and may show sclerotic margins or central calcification, features that can aid in diagnosis. However, in unusual locations such as the orbit or skull base, the radiologic appearance of intraosseous lipomas can mimic more common lesions including fibrous dysplasia, meningioma, or metastatic disease, leading to potential diagnostic challenges[4].

In the optic canal and skull base region, fat-containing or T1-hyperintense lesions may mimic other pathologies, including dermoid cysts, cavernous hemangiomas, and vascular lesions with intralesional hemorrhage. Recognizing this overlap is important, as MRI signal characteristics alone are rarely pathognomonic. CT complements MRI by identifying bone remodeling, sclerotic margins, and intralesional calcifications that may suggest specific Milgram stages and help distinguish intraosseous lipomas from other osseous or extraosseous masses.

In the present case, the lesion was initially suspected to be a lipoma based on MRI characteristics. However, intraoperative exploration and subsequent histopathological analysis revealed an intraosseous lipoma originating within bone, compressing the optic nerve. This finding underscores the importance of correlating radiologic findings with surgical and pathological data, particularly when managing lesions in anatomically complex or diagnostically ambiguous regions. Our experience underscores both the strengths and limitations of MRI in this context: Although it correctly suggested a fat-containing lesion responsible for optic nerve compression, it did not definitively establish the intraosseous origin or exclude other lipomatous and non-lipomatous mimics. This limitation highlights the necessity of correlating radiologic impressions with intraoperative findings and histopathology when managing atypical skull base lesions.

Management of intraosseous lipomas is generally conservative in asymptomatic patients. However, when these tumors cause functional impairment, as in cases of optic nerve compression, surgical intervention becomes necessary[9]. Decompression of the optic nerve may lead to significant visual improvement or stabilization of symptoms. Complete resection is not typically required unless there is suspicion of malignancy or the lesion demonstrates atypical behavior on imaging studies. In this context, preoperative imaging plays a crucial role in surgical planning, enabling the surgeon to assess the lesion’s extent, its relationship to adjacent structures, and to tailor a precise and minimally invasive operative approach.

Our surgical approach incorporated a modified hybrid technique originally described by Tayebi Meybodi et al[10], combining extradural and intradural steps for safe and effective decompression of the optic nerve. The primary benefit of our modified approach included the meticulous opening and decompression of the optic nerve dural sleeve, significantly enhancing visualization and ensuring thorough removal of compressive adipose tissue. This adaptation was crucial in achieving complete decompression without compromising adjacent neurovascular structures, likely contributing to the patient’s significant postoperative visual improvement. Such modifications emphasize the importance of technique evolution tailored to anatomical complexities and lesion characteristics, particularly in rare cases like intraosseous lipoma compressing the optic nerve.

CONCLUSION

This case of intraosseous lipoma of the sphenoid bone compressing the optic nerve in a 41-year-old male highlights the importance of considering rare intraosseous lesions in the differential diagnosis of acute unilateral visual loss. MRI plays an indispensable role in detecting fat-containing lesions and defining their relationship to the optic nerve but cannot, on its own, reliably distinguish intraosseous lipomas from all potential mimics. Definitive management therefore hinges on meticulous surgical decompression and histopathological confirmation. Early recognition and timely optic nerve decompression are essential to prevent irreversible visual damage and to maximize the potential for visual recovery.