Bilateral thinning of the parietal calvarium was noted incidentally. This finding did not directly explain the patient’s symptoms or chief complaint.
In the setting of trauma these lesions can be particularly susceptible to injury.
The patient’s doctor was informed of the findings.
Due to the sharp edges of some of the regions of cortical thinning and adjacent scalp defects, the patient was questioned about any history that could explain this finding.
The patient recalled that prior to her dental reconstruction many years prior, she was asked if bone grafts should be derived from her hip or her skull, and she requested skull bone grafts.
Parietal Calvarial Thinning
The pathophysiology of parietal calvarial thinning (PCT) is incompletely understood but is generally considered a progressive benign disease.
PCT most often affects the elderly with a slight female predilection of 1.9:1.
The incidence in this age group is reported between 0.25-2 percent.
PCT has fascinated scientists and doctors for centuries with studies dating back to the 1700s. PCT was originally thought to be congenital, however it is now assumed to be a progressive disease. Skulls have been studied from around the world dating back as far as the Egyptian Dynasties which demonstrate parietal thinning. PCT has many eponyms: malum senile biparietale, biparietal osteodystrophy, are some of the most historically relevant.
Most often inconsequential, PCT exists on a wide spectrum of severity and at its worst can lead to the creation of susceptible regions of the skull and serious cranial and intracranial injury has results from trauma to these susceptible regions.
The most common presentation is an incidental finding on autopsy or imaging demonstrating varying degrees of thinning extending from the outer table of the calvarium with thinning extending into the diploe. Thinning has been noted to extend through to the inner table.
The affected portion of calvarium most often resides between the sagittal suture and temporal ridge of the parietal skull.
It is most commonly bilateral, however the rate of thinning need not be symmetric.
Deficient osteoclast activity has been identified as a cause, histopathologicaly suggesting a relationship to osteoporosis.
Surgical repair may be indicated with cranioplasty if the erosion is large enough or causes clinically concerning perforation.
Yiu Luk S, Fai Shum JS, Wai Chan JK, San Khoo JL. Bilateral thinning of the parietal bones: a case report and review of radiological features. The Pan African Medical Journal. 2010;4:7.
Durward A. A Note on Symmetrical Thinning of the Parietal Bones. Journal of Anatomy. 1929;63(Pt 3):356-362.
Cederlund CG, Andrén L, Olivecrona H. Progressive bilateral thinning of the parietal bones. Skeletal Radiol 1982;8:29–33.