Bilateral parasagittal pacchionian granulations
A plain anterior-posterior roentgenogram of the skull showed
bilateral subcortical hypolucent cysts in the parasagittal area
(Figure 1). A lateral view showed the location of these cysts to be
in the anterior portion of the parietal bones (Figure 2).
Pacchionian granulations are hypertrophic arachnoidal villi, which
can erode through cranial bone, causing lytic lesions on skull
roentgenograms or computed tomography (CT) scans.
The arachnoid villi are small finger-like projections that
consist of the same cellular and septal mesh that forms the
structure of the arachnoid, but with less septation and larger
spaces. If such villi agglomerate and enlarge, they can form larger
spaces (called fossae lacunas) that sometimes communicate with the
dural sinus through short channels, in which cerebrospinal fluid
(CSF) can be transferred to the venous system. Because of their
close proximity to the cranium, such lacunar spaces can create
imprints on the internal lamina of the cranium as furrows or holes.
If hypertrophic, such arachnoid villi are then called pacchionian
granulations, which can erode even further, reaching the outer
table of the cranium and causing a punched-out lesion on
Pacchionian granulations are reported more frequently among
adults, but earlier stages of hypertrophic arachnoid villi can be
present as early as 18 months of age.2 Typically, they
are asymptomatic and are usually found accidentally on skull
roentgenograms or CT scans, with the typical appearance of
hypodense lesions in the calvarial bone. On T2-weighted magnetic
resonance images, such lesions have a density similar to that of
These granulations are primarily located in the vicinity of
dural venous sinuses and most are close to the sagittal sinus. In
this case, the lesions were located in the parasagittal region of
the parietal bone anteriorly. The posterior part of the frontal
bone is the second most common site.6
Because of the osteolytic appearance of pacchionian granulations
on roentgenograms, the differential diagnosis includes all other
osteolytic lesions of the calvarial bone, including
dermoid/epidermoid cyst, osteoma, enchondroma, fibroma, fibrous
dysplasia, and calvarial hemangioma.7 The typical
parasagittal location, absence of calcification, and the lack of
pain on presentation are distinguishing features. However,
diagnostic biopsy is sometimes indicated, especially if the lesion
is rapidly increasing in size.
Very rarely, hypertrophic archnoid villi are associated with
hydrocephalus, but most cases are asymptomatic and can be observed
Pacchionian granulations are benign overgrowth of arachnoidal
villi that have a radiolucent appearance on a skull X-ray. They
should be considered in the differential diagnosis for any
osteolytic lesions in the parasagittal area.
- Potts DG, Reilly KF, Deonarine V. Morphology of the arachnoid
villi and granulations. Radiology.1972;105:333-341.
- Krmpotic-Nemanic J, Vinter I, Kelovic Z, Suknaic S. The fate of
the arachnoid villi in humans. Coll Antropol.2003;27:611-616.
- Branan R, Wilson CB. Arachnoid granulations simulating
osteolytic lesions of the calvarium. AJR Am J
- Kuroiwa T, Kajimoto Y, Ohta T, Tsutsumi A. Symptomatic
hypertrophic pacchionian granulation mimicking bone tumor: Case
report. Neurosurgery. 1996;39:860-862.
- Tokiguchi S, Hayashi S, Takahashi H, et al. CT of the
pacchionian body. Neuroradiology. 1993;35:347-348.
- Harbert J, Desai R. Small calvarial bone scan foci-normal
variations. J Nucl Med.1985;26:1144-1148.
- Beatty RM, Hornig GW, Hanson EJ Jr. Protruding arachnoid
granulations mimicking dermoid cysts. J Pediatr Surg.
- Gacek RR. Evaluation and management of temporal bone arachnoid
granulations. Arch Otolaryngol Head Neck Surg.