The human frontal lobe comprises approximately 35-40% of the volume of the cerebral hemispheres.¹ It is thus perhaps not surprising that this region of the brain subserves many critical functions. On the dominant side, the inferior part of the frontal lobe (known as Broca’s area, a region of the inferior frontal gyrus) is the center of speech and language production.² A region of the posterior frontal lobe known as primary motor cortex controls motor function on the opposite side of the body. Other portions of the frontal lobe, including the prefrontal cortex, promote empathy, attention to detail, and motivation and form the basis for decision making, personality, and problem-solving capacity.³ Depending on the specific region involved, damage to the frontal lobe can manifest in many different ways. As an example, damage to the posterior right frontal lobe (primary motor cortex) can result in severe left sided weakness. Significant damage to prefrontal cortex can cause a person to become more impulsive or not function appropriately in social situations.⁴ One famous example of the relationship between frontal lobe structure and function is the story of Phineas Gage, an American foreman whose left frontal lobe was impaled by a tamping iron following a railroad blast injury in 1848.⁵ The iron was able to be successfully removed. Incredibly, Gage was able to recover from the injury. Following his convalescence, many observers noted marked changes in Gage’s personality.⁶ Specifically, Gage was reported to have become impulsive and uninhibited—now unable to keep a job. This famous anecdote is a reminder of the complex relationship that exists between frontal lobe function and personality/executive behavior. Changes like those noted in Phineas Gage are often observed by friends and family members of patients who have suffered severe damage to the frontal lobe(s).⁷

In the case of Phineas Gage, penetrating injury from a tamping rod resulted in frontal lobe injury. It is important to remember that, infrequently, damage to the frontal lobe can develop in individuals with no history of trauma—occasionally from unexpected causes like brain tumors. Meningiomas, which arise from the leathery covering of the brain and spinal cord, are an important type of brain tumor that can result in progressive and insidious injury to the frontal lobes. Meningiomas are the most common primary brain tumor—accounting for roughly 35% of primary brain tumors diagnosed each year.⁸ Approximately 10% of intracranial meningiomas arise from a region of the skull base known as the olfactory groove.⁹ While the vast majority of olfactory-groove meningiomas (OGM) are benign and slow-growing, these tumors can sometimes become very large after many years of undetected growth. As frontal lobe dysfunction associated with large OGMs often results in somewhat vague and non-specific symptoms, it is not uncommon for patients to go very long periods of time before these tumors are identified. When massive, OGMs sometimes progress to compress the optic apparatus posteroinferi-orly—symptoms that often lead to imaging and prompt detection.¹⁰ In the following paragraphs, you will hear more about Robert^*: one such patient whose personality, independence, ability to hold a job, and executive function deteriorated over the course of many years. Ultimately, when Robert’s vision started to decline, an MRI ordered by his treating physician identified a massive OGM found to be compressing and damaging both frontal lobes.

In his 40s, Robert was a successful actor in the Cincinnati community, having starred in many successful musicals. At the peak of his career, his friends and family members described him as energetic, meticulous, and a dynamic performer. As he aged, many around him noted that Robert seemed to care progressively less about specific details. Robert’s performance as an actor began to gradually decline. Eventually, friends and family were forced to place Robert in an assisted-living facility, under the supervision of a caregiver. Because he suffered from type II diabetes, Robert required an annual visit to his eye doctor or ophthalmologist. On one such visit, Robert’s vision, which previously had been perfect, was noted to have gotten slightly worse. New, minor visual loss involving the temporal field of the left eye was detected. Robert’s ophthalmologist initially felt that he might be suffering from glaucoma, a common eye condition caused by increased pressure in the eye. However, additional testing was negative for increased intraocular pressure. As the visual loss was minimal, and Robert didn’t seem to be particularly concerned, the medical team decided to monitor conservatively. Over the next few years, the vision in Robert’s left eye deteriorated further, and he began to lose vision in the temporal field of his right eye as well. Formal testing demonstrated that Robert’s now had bitemporal hemianopsia, a pattern of visual loss in the outer half of the visual fields in both eyes known to be concerning for a structural or compressive etiology.

During the same period of time his vision had inexplicably worsened, Robert’s caregiver began to notice additional changes in his personality. Every day, Robert seemed a little less like himself. He was sleeping more than usual and now missing many of the community events he would previously attend. When Robert stopped checking his blood sugar levels and taking his medications, his caregiver felt something was very wrong. In light of both the vision and personality changes, Robert was ultimately referred to a neurologist. In addition to Robert’s deterioration in vision and personality, detailed neurologic testing in neurologic clinic also revealed anosmia or loss of smell with associated deterioration in taste. Anosmia is yet another symptom commonly observed with massive OGMs that often goes initially undetected; progressive enlargement of olfactory groove meningiomas stretches the olfactory nerve(s), often resulting in loss of smell in large or massive OGMs.¹¹ Following thorough evaluation in neurology clinic, magnetic resonance imaging (MRI) of the brain was ordered. These images demonstrated a massive tumor originating from the olfactory groove (Figure 1.1). The tumor extended posteriorly to compress Robert’s optic chiasm—explaining his progressive visual loss. The massive tumor could also be seen to displace and compress both frontal lobes, providing an explanation for the pronounced changes in personality and executive function his family and caregivers had noted. On MRI, the appearance of the tumor was most consistent with an olfactory groove meningioma.

After the report from the MRI returned, Robert was referred to Dr. Jonathan Forbes, a neurosurgeon specializing in skull base tumors. Dr. Forbes explained to Robert that, without surgery, the tumor would continue to grow and further impair his vision and personality. With surgery, Robert’s vision was likely to improve. It was also likely that removal of the tumor would help Robert regain some element of frontal lobe function. Though hearing about the surgery was scary, Robert and his family knew the tumor had to be removed (Figure 1.1A). Dr. Forbes performed a technique often used for large tumors in the anterior skull base called a bifrontal craniotomy (Figure 1.1B).¹² After removing a portion of the skull bone covering the frontal lobes, he opened the dura mater—the tough outermost layer of the meninges covering the brain. The tumor was de-vascularized from its origin along the olfactory groove and debulked using a device called a sonopet. The tumor could then be meticulously dissected from adjacent healthy brain tissue. With the aid of high magnification, Dr. Forbes carefully dissected the tumor from Robert’s optic nerves and pituitary stalk. The entire tumor was removed and sent to pathology, confirming a benign meningioma.

Robert did well after the surgery, noting instantaneous improvement in vision, and was discharged after a few days in the hospital. A year after his surgery, Robert returned for a follow-up appointment. Repeat MRI showed no trace of any residual or recurrent tumor (Figure 1.3). At this time, both Robert and his caregiver had noted considerable improvement in Robert’s personality and level of executive function. One year following surgery, Robert felt more like himself again. He had regained the capacity to cook his meals and check his blood sugar daily. For Robert, however, the best part of his recovery was finding a way to return to help with the community plays he loved so much.

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* a pseudonym